plethora of ne 555 data

Copyright © January 28th 1996 - Updated April 27th 2010 ..... Brought to you by Unitech Electronics Pty. Ltd.

Following in the footsteps of the "primitive" but quite successful 4 pin OM802 timer IC manufactured by the original SIGNETICS ITT -

- GEMINI plants way back in 1969/1970, a new and very innovative IC known as the NE-555 timer IC was released to the masses,

being introduced around May 1971 by the then Signetics Corporation, later to be taken over by Philips semiconductor, then

more recently, NXP Semiconductor as a division of Philips.

It then to become known as the NE-555 / SE-555 which we all know today as the "The Ubiquitous Timer chip" and it was also

the very first very mass-produced commercially produced timer IC available at that time.

The design team had no real idea what product life it would have, nor how brilliantly successful it would be, lasting well over 25 years

still in mass-production even today. [ 1971- 1996 ] and it is still sold and used in electronic circuitry in March 2010, some 39 years later.

CLICK THE OM 802 CHIP

A Plethora Of NE-555 data - NE555 Tutorials Page http://www.unitechelectronics.com/NE-555.htm

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The NE-555 would prove to be a " hit " and provide Electronic Engineers, Circuit Designers and a host of "Hobby Tinkerers" with a

relatively novel and highly economical timer chip that was indeed very stable at timing all the way up to its maximum timing or

oscillating frequency of ( at the time ) 200KHz and in a very short time proved to be a very "user-friendly" timer integrated circuit

for both simple and complex monostable as well as brilliant astable ( or multi-vibrator ) applications.

The NE-555 was invented by a clever Swiss born gentleman by the name of Herr. Hans. R. Camenzind. (Pictured) in 1970, the NE-555

went on to become a legend in the Electronics industry, the chip possibly deriving its "nick-name" from the three 5K resistors,

R7, R8 and R9, all of which form the very unique " five - five - five " resistor combination.

Since this versatile little device became commercially more available in May 1971, a plethora of highly innovative and very unique and

"ever-so-ingenious" circuits has emerged and many circuits have been developed and demonstrated to the "N-th" degree in a variety

of highly reputed "trade-only" journals, professional "Engineering Monthly" magazine journals as well as the vast numbers of excellent

"Hobbyist/Professional" publications globally, the likes of Leo Simpson's SILICON CHIP, ELEKTOR, Practical Electronics (PE),

Electronics Australia (EA) and Electronics Today International (ETI) to name but just a mere few.

During the past twelve or so years since 1971, some " NE-555 " manufacturers have ceased existing in the market, perhaps to stiff

competition, or purely being consumed as a "valued asset" by much larger companies swallowing-up smaller manufacturers, thus

perpetuating their guaranteed and very much continued successful sales of this ever so popular chip, the NE-555.

Update: 29th March 2003

Please note: Electronics Australia (E.A.) and Electronics Today International (E.T.I.) have ceased to be published, leaving only the

brilliant monthly "magazine" SILICON CHIP as the only high quality electronics magazine published now in Australia for both the

"Hobbyist" and the "Professional" users alike. Check out Silicon Chip Magazine right here or later on.

SILICON CHIP is available monthly from Jaycar or Altronics Stores, local newsagents or mailed directly to you by subscription with

the publisher across Australia (ring your local store first as S. C. moves quickly off the shelves). International readers, we invite you

to subscribe to SILICON CHIP for continued updates in the industry as well as very well researched cutting edge electronic projects.

Many other companies, like N.T.E. (a subdivision of Philips) picked up where some "left off". See the Manufacturers list we compiled.


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This restructuring was followed by N X P (Philips). This article is about this fantastic little timer IC which is, after 25 years ( 1996 ),

was still very popular today and used in many schematics that can be viewed on the " internet ". Slowly a new generation of "useful chips"

called PIC chips are taking over for many functions, these seem to be the greatest thing since the introduction of the now famous "NE-555".

The PIC Chip introduced some years back has the brilliant capability of being able "programmed" just like a small CPU and to be custom

tailored via very small and byte efficient programs to execute a myriad of unique functions, from sirens, monitoring etc. to very accurate

timers.

In this article (only this page) we will deal solely with the "NE - 555" applications and the easy to setup usefulness of this chip.[ 1971- 1996 ]

Although these days the CMOS version of this IC, like the Motorola MC1455, is mostly used, the regular type is still

very much available and used often today, it is still in great demand due to its efficient switching characteristics and very low cost.

There have been many improvements and variations in the "internal" circuitry since 1971, too many to list here, however we invite you to

check out our NE - 555 PDFs covering many package versions of this rather unique and special chip.

With all these "hidden" improvements within the various NE-555's manufactured, the main NE-555 package is still very much virtually

pin-for-pin compatible with every other NE-555 on the market today, this also includes the NE-7555 a later marketed CMOS version of

the NE-555.

The aim within this simple tutorial is to show in some easy to comprehend detail, exactly how the NE-555 timer is correctly used.

The standard NE-555 can be a stand-alone compact device, yet powerful enough to perform basic timing functions or as a versatile timer

or even as a simple oscillator to create tones of various pitches up to the ultrasonics of 200KHz.

The NE - 555 can be easily combined with other ancillary circuitry employing gates or transistors for current switching or with other

solid state devices without the mandatory requirement of an electronics engineering degree. How good is that ? It does not get any better!

This brilliant timer uses about 25 transistors to perform the tasks and is coupled with various diodes and resistors all on the NE-555's

substrate "die" to do their bit in switching and timing and for this task, it is done with the minimum of external passive components.

Shown here, is a more simplified ( but quite accurate ) block diagram in Fig.3 to explain the basic internal organizations of the NE-555.


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In Table 1 ( above ), we have alphabetically listed 27 types of NE - 555 manufacturers, both past and present (as at Dec 2007 ) with

their part numbers. Some are listed under two part numbers, check with our's or other's data sheets for Military specification or MIL SPEC.

Some are ceramic cased. These are reported to have somewhat improved electrical and thermal characteristics over their commercial generic

counterparts and a more expensive in comparison to the generic NE-555 sold throughout the world via electronics wholesalers and retailers

such as ourselves and are typically the standard 8 PIN Dual In Line (DIL) plastic package. We can supply MIL SPEC as requested at a higher

that normal price. We believe that both the ceramic and the round T-05 "tin can" Packages are still available at the time of writing this page.

Note: A recent innovative company, Custom Silicon Solutions Inc, has produced a "hybrid" variety of the famous NE-555 with is very own

six-decade programmable counter, an on-board EEPROM and the CSS-555C includes an internal 100pF timing capacitor. It is pin-for-pin

compatible with the standard 555 timer and features an operating current under 5µA. Its minimum supply voltage is 1.2V, making it brilliantly

ideal for battery operated applications as well as a variety of other low power consumption devices. Smart and innovative, this CSS-555C !


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MIL SPEC.

While on the subject of MIL. SPEC. or Military Specification, it is generally not realised that Mil. Spec. chips are basically the same as any

other chip, however their AQL or Acceptable Quality Level is tightened right down and the permissable errors in a sample 100% tested batch are

virually zero, that is to say, in say a batch of 100 chips, 99% passed with flying colours and 1% is a "bit suss" and pass all basic functionality

tests however they do not meet the 100% AQL and therefore can be safely sold as garden variety commercial chips.

Having said that, one can purchase a batch of 100 pieces of NE-555 chips, test every single one for all the correct parameters that will ensure that

each and every chip is fully functional, have each chip "burned in" at its maximum recommended supply voltage overnight on a specific "test bed" and

see how many pass or fail, the passes "could" basically be classed as "Mil. Spec."

Also, Having noted that, it would be safe to say that certain chips in that control batch of a mere 100 chips could actually perform a small

percentage better than others in the batch, it would be unreasonable not to expect this result from a quantity of only 100 pcs of mass

manufactured NE - 555 chips.

This however dispels the myth and story that manufacturers make special chips, manufactured with extra bits or thicker substrate, thicker

attaching wires, increased substrate pads areas and so on... to special specifications, calling them MIL.Spec. It simply is not so.

We invite any LINEAR, LOGIC or ANALOG chip manufacturer to write to us and prove us 100% wrong.

Our email is: [email protected]

To date, not one chip manufacturer has written to us to explain that there are in fact specially manufactured chips as MIL. Spec.


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The NE-555, in figure 1 (above) is supplied in a plastic package. It is believed that the round metal-can called the ' T-05 ' package

or the "tin-can" is no longer available in favour of the more familiar and cheaper to produce 8-pin DIP "Dual IN-Line plastic" package.

About 20 or so years ago the "T-05" metal-can type was very much the standard with the early SE-555 and NE-555 types .

The NE-556 timer is a dual version of the NE-555 and comes in a standard 14-pin DIP plastic package, with two NE - 555 timers within.

The NE-558 was a quad version of the NE-555 with four distinct NE-555's within the one package, incidentally in a 14 pin DIP case, however

it was scheduled to be discontinued due to its lack of popularity and also more importantly, its own inherent internal "noise" problems.

Within the NE-555 timer, in figure 3 (above) there are the equivalent of over 26 semiconductors and about 15 resistors, depending on the

actual manufacturer. The representative equivalent circuit depicted in Fig.4 B here in block diagram, shows the provision of the functions

of "control", "triggering", "level sensing" or "comparison", "discharge" and most importantly, the "power output". Note the three 5K resistors.

Note: The use of C2, typically 10 Nanofarads (nF) assists in "good house-keeping" in keeping "internal noise" down. It accesses directly

the inverting input of the upper comparator which is incidentally connected (inside the chip) between the first and second of the 5K resistors

which will be discussed further on in this tutorial , down the page under the heading Pin 5 ( Control Voltage ).


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Some of the more attractive features of the recent NE-555 timers are: Supply voltage between 4.5 volts and 18 volt, supply current of between

3 to 6 mA and a Rise / Fall time of 100 nSec.

The NE-555 performs best with a stable supply voltage with good low ESR filter capacitors to keep the "lines" clean.

It can also withstand quite a considerable amount of "reasonable" abuse, though it does not handle reverse polarity power.

Note: in Figure 3 ( above ) the common threshold current is in fact determined by the maximum value of Ra + Rb.

For typical maximum 15 volt operation the maximum total resistance for R (Ra +Rb) is 20 Meg-ohm, please bare this in mind.

The supply current, when the output is 'high', is typically around 1mA (milli-Amp) or less. According to the specs, the initial monostable timing

accuracy is typically within 1% of its "calculated" value, and exhibits negligible ( 0.1%/V ) drift with regards to supply voltage.

Thus it can be realised that long-term supply variations can basically be ignored and the temperature variation is only 50 ppm / °C ( 0.005% / °C ).

R - C Networks

All IC timers rely upon an external capacitor to determine the off-on or on-to off time intervals of the output pulses.

You may recall from your own personal experiences in a study of basic electronics, it takes a finite period of time for a capacitor (C) to charge or

to discharge expotentially through a resistor ( R ). Those times are clearly defined and can be calculated given the values of resistance and capacitance.

The basic RC charging circuit is shown in fig. 4.(below) So, assuming for a moment that the capacitor ( C ) is initially discharged, when the switch is closed,

the capacitor begins to charge through the resistor via Ra and RB. The voltage across the capacitor rises from zero up to the value of the applied DC voltage.

The charge curve for the circuit is shown in fig. 6 (below). The time that it takes for the capacitor to charge to approx. 63% of the applied voltage is known as

the time constant (t). That time can be calculated with the simple expression:

Looking at the voltage charge versus time curve in figure 6. you can see that it takes approximately "5 complete time constants" for the capacitor to charge

to almost the applied voltage. Theoretically, it would take about 5 seconds for the voltage on the capacitor to rise to approximately the full 6.0 volts.


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t = R X C

Let's assume that a resistor in this circuit has a value of 100K ohm and that the capacitor's value is 10 uF (micro-Farad).

The time constant in this case is:

t = 100,000 x 0.00001 = 1 second

Let's further assume that the applied voltage is exactly 6.000 volts.

That is to state that it will take one time constant for the voltage across the capacitor to reach the approx. of 63 % of the

applied voltage of 6.0 volts.

Therefore, theoretically, the capacitor charges to "approximately" 3.78 volts in one second.


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In Figure 4 A (above), a change in the input pulse frequency allows completion of the timing cycle.

The accepted rule is that the monostable 'ON' time is set to approximately 1/3 longer than the expected

time between the actual "triggering pulses". Create your own "test circuit" and observe it on your C.R.O.

This circuit is more often referred to simply as a "Missing Pulse Detector" circuit.


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Definition of Pin Functions:

Refer to the internal 555 schematic of Fig. 3 (above)

Pin 1 ( Ground ):

The ground ( Earth, Deck or Common ) pin is the negative (-ve) voltage supply of the device, which is connected to circuit

common (ground) when operated from positive (+ 4.5V - + 15V DC) supply voltages. This pin is ALWAYS grounded.


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Pin 2 ( Trigger ):

Pin 2 is the access "input" to the lower NE-555's comparator and is used to set the latch, which in turn causes the

output to go high. This is the initialising of the timing sequence in monostable operation and the triggering process is

accomplished by taking the pin from "above" to "below" a voltage level of 1/3 V+ or, in general, 1/2 of the

apparent voltage appearing at pin 5. This action of the triggering the input is "reasonably" level sensitive, thus allowing

notably slower rates of change in the wave forms, as well as "pulses", it can also be used as "triggering" sources.

Note that the trigger pulse must actually be of shorter duration than the time interval determined by the external R and C.

When pin 2 is held low longer than that, the resultant output will remain high until the trigger input is driven high once again.

One precaution that should be observed with the trigger input signal is that it must not remain lower than 1/3 +VCC for a

period of time longer than the timing cycle. If this is allowed to occur, the timer will always re-trigger itself upon termination

of the first output pulse. Thus, when the timer is driven in the monostable mode with input "pulses" longer than the desired

output pulse width, the input trigger Pin 2 should effectively be shortened by differentiation. This fact can be a useful feature.

The minimum-allowable pulse width for actual triggering is virtually dependent upon pulse level, but in reality if the pulse is

greater than the 1 micro-Second (uS), general triggering will be quite reliable. Always be mindful and take precautions with

the "storage" time in the lower comparator. Always bare this in mind in your designs, especially in "tight" timing circuits.

This area of the NE-555 circuit can exhibit normal "turn-off" delays of several (uS) microseconds after triggering, ie: the latch

can still "hold" a trigger input for this period of time after the trigger pulse. Spooky eh? Not really, in reality this means

that the minimum "monostable" output pulse width should be in the order of 10uS (micro-seconds) to prevent possibility of double

triggering due to this unusual effect.

The input voltage's range that can be quite safely applied to the trigger pin 2 is anywhere between +Vcc and ground, or

basically +ve supply and zero. A "dc current", termed the Trigger current, must also flow from this terminal into the

external circuit. This flow of current is typically around 500 nano-Amps (nA) and will define the upper limit of resistance

allowable from pin 2 to ground.

For an astable (multivibrator) configuration operating at +VCC = 5 volts, this resistance is about 3 Mega-ohm, however it can


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be greater for higher +VCC levels but not to exceed 10 Meg Ohms.

Pin 3 ( Output ):

The output Pin 3 of the NE-555 comes from a high-current pseudo "totem" pole arrangement made up of internal

transistors Q20 - Q24. Transistors Q21 and Q22 in a "Darlington" configuration, provide the drive for source-type

loads, whereas Q22 is performing the switching here. The Darlington configuration provides a high-state output voltage

of around 1.7 volts less than the +VCC supply level used.

The Q24 transistor provides current-sinking capability for low-state (low Logic) loads referred to +Vcc ( as found

in typical TTL inputs). Q24 also maintains a low saturation voltage, which allows it to nicely interface directly,

while facilitating a good noise margin, when delivering current sinking logic levels. Q20 is the main culprit is doing

the "official" switching is Q17, outputs depend on what is at Q17's base.

It is true to state that output saturation levels vary markedly with relation to supply voltage, it can however be said

that the same rule applies to both high states and for low states. At a +VCC of 5.00 volts, for a example, the low "logic"

state Vce ( sat ) can be measured at around 0.25 volts at a mere 5.00 mA. While operating at 15.00 volts, however,

it can easily sink 200 mA if an output-low voltage level of around 2.00 volts is permissible, bearing in mind that the

general total power dissipation should be always noted in all such instances. NE-555 chips can indeed get very hot when

"over-driven" and this factor alone can affect the internal stability by continued operation at much higher temperatures.

An important or even perhaps a crucial suggestion would be to add an external "drive" transistor that can handle an

increased load in line with current considerations (see Fig. 5B) the pin 3's "load" with a transistor


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and its base drive resistor with the desired current switching in mind from pin 3.This transistor can be anything

from a humble small 800 mA current switching 2N2222 to a BD681 Darlington switching around 4 amps. Both will work.

Pin 3 ( Output ) Cont'd:

What is termed a "high-state" level or logic high is to the order of about 3.3 volts at +Vcc = 5.00 volts, about 13.30 volts

at +Vcc = 15.00 volts.

Note that both "Rise" and "Fall" times of the output waveform are typically quite fast, with average switching times being

to the order of around 100nS (nano-Seconds).

Nothing in general electronics is 100% absolute, hence the use of terms "around" and "about", due to component tolerances.

In doing your timing/switching experiments, always observe the fast switching characteristics on a C.R.O.( Cathode

Ray Oscilloscope ) or a L.C.D. Digital Oscilloscope.

When using a RX external transistor, Figure 5 B make sure the base is saturated just enough with input voltage/current

but not overdone. That is to say, not being "over-driven" with regards to driving the base of the transistor too hard, thus

possibly frying the transistor.

This could be any value between 820 Ohms up to 3K3 or beyond, depending also on the voltage/current consumed by

the switched device, for example, a 300 Ohm relay. Do your maths and calculate the desired switching voltage/current.

The state of the logic state of the latch will always be the reverse of the output pin 3, and this fact may be observed

by examining Figure 3.

Since the latch itself is not directly accessible, this relationship may be best explained in terms of latch-input

trigger conditions.

To trigger the output to a high condition, the trigger input is momentarily taken from a higher to a lower level.

[see "Pin 2 - Trigger"].

This causes the latch to be set and the output to go high logic.

Actuation of the "lower" comparator is the only manner by which the Pin 3 output can be switched to a high logic state.

The Pin 3 output can revert to a low state of logic by allowing or forcing the "threshold" Pin 6 to go from a low state

of logic level to a higher state logic level (see "Pin 6 - Threshold"), which resets the 555's latch.


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The output can also be made to go low by taking the reset to a low state near ground (see "Pin 4 - Reset").

The output voltage available at this pin is approximately equal to the Vcc applied to pin 8 minus 1.7V.

Pin 4 ( Reset ):

Pin 4 is used to "reset" the NE-555/s internal latch and restore the output to a low logic level.

The actual "reset" voltage threshold level is about 0.7 volt, and resetting requires a sink current of

around 0.1mA to perform the reset of the NE-555 chip.

These levels operate fairly independently of the operating +Vcc level, resulting in the reset input

being TTL compliant with any supply voltage between 4.5 Volts and 15 Volts D.C.

Pin 4 the reset input is an over-riding function, that is to say, it will actually force the output

to a low logic state with total disregard of the state of either of the other "inputs".

It can be employed to terminate an output "pulse" earlier than expected or to gate oscillations

from an "ON" state to an "OFF" state etcetera.

The delay timing from resetting to output is typically on the order of about 0.5 µS, and the minimum

reset pulse width is around 0.5 µS. These timing figures are "generalised" and will vary from

one NE-555 manufacturer to another, based on tolerances and "die" lithography, processess and assembly.

Pin 4, the reset pin is primarily used to specifically reset the flip-flop that controls the logic

state of output from pin 3.

The "reset" pin is activated when a level as low as 0 (zero) and up to 0.4 volts voltage is presented to this pin.

Pin 4 once activated, will in turn force Pin 3 to drop to a low logic level irrespective of what state any


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of the other inputs to the internal Flip-Flop are. Basically it over-rides all. In utilising the NE-555, we suggest

tying this pin to +VCC in most situations where the reset pin is not being directly employed as such.

This will avoid a "false" reset situation whereas the NE-555 in some circumstances could possibly reset

without notice.

Pin 5 ( Control Voltage ):

As mentioned earlier, the NE-555 has three 5K ohm resistors (R7, R8 and R9) in series forming an equal voltage

divider thus as 1/3rd, 2/3rd's within. Pin 5 provides for direct access to the 2/3 +Vcc of this unique voltage divider

reference point, the referenced level for the NE-555's upper comparator. It also facilitates indirect access to the lower

NE-555's comparator, as there is a 2 : 1 ratio divider via R8 and R9 from this point to the lower-comparator reference

input at transistor Q13.

It is in fact optional to utilise this pin 5. It can be called a "user pin" and it does allow some unique flexibility by permitting

alteration to the timing period, re-configuring the R7 value to less than 5K ohms thus customising the "resetting" of the comparator,

etcetera. When the NE-555 timer is used in a "voltage controlled" mode, its operational ranges will vary from about 1.00 volt less

than +VCC and down to within 2 volts of ground, although this is not guaranteed in print on the NE-555 specifications sheet.

Voltages lower than 15 Volts (maximum supply voltage) can be safely applied outside these limits, however they should

realistically be confined to be within the limits of +VCC and ground (0V) for higher reliability.

By applying a voltage to Pin 5, it is in fact possible to vary the actual timing of the device totally independent of the RC network.

The control voltage may be varied from around 45% to about 90% of the +Vcc in the monostable mode, making it quite possible to

control the width of the output pulse quite independently of RC. When it is used in the astable mode or ( multivibrator) mode, the

control voltage at Pin 5 can be varied from around 1.7V to the full 15V +Vcc and not over.

Indeed, by varying this voltage at Pin5 in the astable mode, it will produce a frequency modulated (FM) output.

IF the control voltage Pin 5 is not used, it is recommended in the specifications that it be bypassed, to ground (0V),

with a capacitor of about 10nF (nano-Farads) for good immunity to noise on the upper comparator's input (non-inverting).


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It is not quite obvious to perform this as in many NE-555 circuits we have seen since have absolutely no by-pass capacitor

off Pin 5 to ground. After reading the NE-555 specifications sheet, one can realise the good value in adding this capacitor.

Don't skip doing it. The small 10nF ceramic cap may also eliminate false triggering and let's face it, they are cheap.

Pin 6 ( Threshold ):

Pin 6 is one input to the upper comparator ( inverting ) the other being Pin 5 which is used to reset the latch,

which results in the output to going low logic.

A reset of the NE-555 can be accomplished via Pin 6 by taking Pin 6 from below 2/3rds +VCC to above

a voltage level of 2/3 +VCC which incidentally is about the normal voltage on pin 5.

The action of the threshold Pin 6 is fairly "level sensitive", allowing for slow rate of change type waveforms.

Build your very own NE-555 tester and observe these various readings on your oscilloscope.

Note the noise on the power source input +VCC if there are no filtering capacitors to clean up the inherent noise

from within the NE-555 chip.

Add more "filter" capacitors and see the difference for yourself. Remember Pin 5 with its own 10nF ceramic capacitor.

The wave forms are fascinating to watch and learn from and apply to other useful project directions.

At Pin 6 the voltage range that can safely be introduced to the threshold Pin 6 is between +VCC and ground 0V.

A "DC current" referred to as the Threshold Current must also flow into Pin 6 from the external circuitry.

This "DC current" is typically to the order of around 0.1µA,(micro-Amp) and will actually define the "upper limit" of

the "total" resistance allowable from Pin 6 to +VCC.


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For either timing configuration operating at +VCC = 5.00 volts, this resistance is very close to 16 Meg-ohms. Use DMM.

Doing the maths, For 15.0 volt operation, the maximum value of resistance is around 20 Mega Ohms.

Pin 7 ( Discharge ):

Pin 7 is connected to the Open Collector of Q14, an NPN transistor, the emitter is connected to ground, so that when

the Q14 transistor is turned "ON", Pin 7 is directly "shorted" to ground potential.

Typically the timing capacitor C 1 is connected between Pin 7 and ground 0V and is discharged only when the transistor

turns "on". The conduction state of the Q14 NPN transistor is basically identical in "timing" to that of the "output" stage.

It is "on" [ ie: low resistance to ground ] when the output is low and "off" [ high resistance to ground ] when the

output is high. In both the monostable and astable ( multivibrator ) time modes, the Q14 NPN transistor switch is

used to clamp and hold the appropriate "nodes" of the timing network to ground 0V. The Q14 base saturation voltage is

typically below 100mVs (milli-Volts) for designated currents of around 5 mA or less and the off-state leakage current

is about 20nA (nano-Amps) measurable (only just). Note this is not as far as we know, written in the NE-555 spec sheet.

Note: The maximum collector current of Q14 NPN transistor is internally limited by the design, thereby removing any

possible or potential restrictions on the capacitor C 1's size due to peak "pulse" current discharge. We suggest

not using capacitors as high as, for example, 4700 uF as the collapse current may do some internal damage to the


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NE-555's Pin 6 open collector Q14 NPN transistor. Be very much aware of this factor.

In certain circuit applications, this open collector Q14 NPN transistor output can be used as a pseudo- auxiliary output

terminal, with its own small current sinking capability similar (but not as high) to the output (pin 3).

Pin 8 ( Vcc +ve ):

The +VCC Pin 8 is the positive supply voltage pin of the NE-555 timer IC.

The supply voltage operating range for the NE-555 is + 4.5 volts (minimum) to +15 volts (maximum),

and is specified for operation range of between +5 volts and +15 volts.

The NE-555 timer device will operate basically the same over this wide range without any noticeable change in timing period.

The most significant notable operational difference is the output Pin 3 drive capability, which increases for both current

and voltage range as the supply voltage is increased.

Sensitivity of the time interval to supply voltage change is typically very low, usually around 0.1% per volt or less.

Note: We discussed Military specification chips previously and there are claims that special and "MIL-SPEC" military devices

are available that operate at voltages as high as 18 volts. As mentioned, a control batch of , say 100 chips of NE-555 will exhibit


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various "operating characteristics" though, it is rumored that some NE-555's do run as high as 18 Volts D.C. We need to test these

before we can safely state that this is in fact correct and the details above will be alter to reflect these "testing" results. (1996)

NE-555 Pocket tester - A Simple go / No-Go tester

Build yourself a simple NE-555 test circuit of Figure 5 (above) to get you going and test


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all your NE-555 timer ic's. You can instantly check to see if they are functioning.

Another use is as a NE-555 "trouble shooter" circuits. This tester will tell you if it's a goer.

Make sure the NE-555 goes in the correct way as per the drawing. Otherwise, smoke may will result !

Remember this rule, never oscillate an old NE-555 I.C. in excess of 200KHz, smoke may occur !

In Figure 5A we have provided you with a Vero-Board layout complete with all cuts made to form the circuit.

NE-555 TIME CONSTANTS - Simple graphical representations

The capacitor charging slows down as it nears its expected charge however, in actual fact it never

reaches the full +Vcc supply voltage. Please note: This is the nature of the beast, remember this.

That being the case, the maximum charge it receives in the timing circuit (66.6% of the supply voltage)

which is a little over the charge received after a time constant ( 63.2% ). ( Q = I x t )


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The capacitor discharges slowly down until it almost discharges fully, however they never quite reach

the ground potential, this is also the nature of the beast. This means there will always be a minimum

voltage present in a circuit that can be measured in as it operates at greater than zero. In some cases,

it is desirable to place a high value resistor across the supply rails to help "bleed-out" the capacitors.

The Timing circuit is approximately 63.2% of the +Vcc supply voltage.


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The discharge time (t) of a capacitor to discharge expotentially to a theoretical zero also takes time

and this can be shortened by decreasing resistance (R) to the flow of current. (t= R x C )

Without a doubt, waiting for the capacitor to charge while holding a stopwatch has to be up there

with watching grass grow, especially if the capacitor "C" is 1,000uF and the "R" is 1Meg or larger.

This can literally take over 1 hour for the whole thing to change state, while observing on the CRO.

So, We built a special digital timer, counting upwards and incrementing and only displaying in seconds

and triggering off the NE-555's "change in state" to do this mundane task. Observing this without the

digital seconds counter would have been about as exciting as watching paint dry,.... seriously.

Basic NE-555 Operating Modes:

The NE-555 timer has two basic operational modes: one shot (monostable) and the other as astable.

In the one-shot mode, the NE-555 acts like a monostable multivibrator. A monostable is said to

have a single stable state and that is the "off" state. Whenever it is triggered by an input

pulse, the monostable switches to its temporary state. It remains in that state for a period

of time determined by an R-C network. It then returns to its stable state, awaiting a possible trigger.

So, in other words, the monostable circuit generates a single pulse of a fixed time duration each time


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it receives and input trigger pulse. Thus the name one-shot. One-shot multivibrators are used for

turning some circuit or external component on or off for a specific length of time. It is also used to

generate delays. When multiple "one-shots" are cascaded, a variety of sequential timing pulses can be

generated. Those pulses will allow you to time and sequence a number of related operations.

The other basic operational mode of the NE-555 is as and astable multivibrator. An astable multivibrator

is simply and oscillator. The astable multivibrator generates a continuous stream of rectangular off-on

pulses that switch between two voltage levels.

The frequency of the pulses and their duty cycle are dependent upon the R-C network values.

Basic NE-555 One-Shot ( Monostable ) Operation:

Fig. 4 shows the basic circuit of the NE-555 connected as a monostable multivibrator.

The use of the word "multivibrator" here implies it oscillates, well, it does but once only.

It should be referred to as a "toggle-ator" as it toggles from one state and stops in another

state, ie: going from high to low or low to high, depending on the circuit it is being used in.

An external RC network is connected between the supply voltage and ground.

The junction of the resistor and capacitor is connected to the threshold input

which is the input to the upper comparator.

The internal discharge transistor is also connected to the junction of the resistor

and the capacitor. An input trigger pulse is applied to the trigger input, which is

the input to the lower comparator.

With that circuit configuration, the control flip-flop is initially reset.

Therefore, the output voltage is near zero volts.

The signal from the control flip-flop causes T1 to conduct and act as a short

circuit across the external capacitor. For that reason, the capacitor cannot charge.

During that time, the input to the upper comparator is near zero volts causing the

comparator output to keep the control flip-flop reset.


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Notice how the monostable continues to output its pulse to pin 3 regardless of

the inputs "swing" back up. The reason for this is because the output is only

triggered by the input pulse, the output actually depends on the capacitor charge CX.

Basic NE-555 Monostable Mode:

The NE-555 in fig. 9 A is shown here in it's utmost basic mode of operation as

a triggered monostable. One immediate observation is the extreme simplicity

of this circuit. Only two components to make up a timer, a capacitor and a resistor.

And for noise immunity maybe a capacitor on pin 5.

Due to the internal latching mechanism of the NE-555, the timer will always

time-out once triggered, regardless of any subsequent noise (such as bounce)

on the input trigger (pin 2).

This is a great asset in interfacing the NE-555 with noisy sources.

Just in case you don't know what 'bounce' is: bounce is a type of fast,

short term noise caused by a switch, relay, etc. and then picked up by the input pin.


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The trigger input is initially high (about 1/3 of +V).

When a negative-going trigger pulse is applied to the trigger input (see fig. 9a), the

threshold on the lower comparator is exceeded.

The lower comparator, therefore, sets the flip-flop. That causes T1 to cut off, acting as

an open circuit. The setting of the flip-flop also causes a positive-going output level

which is the beginning of the output timing pulse.

The capacitor now begins to charge through the external resistor.

As soon as the charge on the capacitor equal 2/3 of the supply voltage,

the upper comparator triggers and resets the control flip-flop.

That terminates the output pulse which switches back to zero.

At this time, T1 again conducts thereby discharging the capacitor.

If a negative-going pulse is applied to the reset input while the output pulse

is high, it will be terminated immediately as that pulse will reset the flip-flop.

Whenever a trigger pulse is applied to the input, the NE-555 will generate its

single-duration output pulse. Depending upon the values of

external resistance and capacitance used, the output timing pulse may be

adjusted from approximately one millisecond to as high as on hundred seconds.

For time intervals less than approximately 1-millisecond, it is recommended that

standard logic one-shots designed for narrow pulses be used instead of a NE-555

timer. IC timers are normally used where long output pulses are required. In

this application, the duration of the output pulse in seconds is approximately

equal to:

T = 1.1 x R x C (in seconds)

The output pulse width is defined by the above formula and with relatively few


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restrictions, timing components R(t) and C(t) can have a wide range of values.

There is actually no theoretical upper limit on T (output pulse width), only practical ones.

The lower limit is 10uS. You may consider the range of T to be 10uS to infinity,

bounded only by R and C limits.

Special R(t) and C(t) techniques allow for timing periods of days, weeks, and

even months if so desired.

However, a reasonable lower limit for R(t) is in the order of about 10Kilo ohm,

mainly from the standpoint of power economy.

(Although R(t) can be lower that 10K without harm, there is no need for this

from the standpoint of achieving a short pulse width.) A practical minimum for

C(t) is about 95pF; below this the stray effects of capacitance become

noticeable, limiting accuracy and predictability. Since it is obvious that the

product of these two minimums yields a T that is less the 10uS, there is much

flexibility in the selection of R(t) and C(t). Usually C(t) is selected first to

minimize size (and expense); then R(t) is chosen.

The upper limit for R(t) is in the order of about 15 Mega ohm but should be

less than this if all the accuracy of which the NE-555 is capable is to be achieved.

The absolute upper limit of R(t) is determined by the threshold current plus the

discharge leakage when the operating voltage is +5 volt.

For example, with a threshold plus leakage current of 120nA, this gives a

maximum value of 14M for R(t) (A very optimistic value).

Also, if the C(t) leakage current is such that the sum of the threshold current

and the leakage current is in excess of 120 nA the circuit will never time-out

because the upper threshold voltage will not be reached.

Therefore, it is good practice to select a value for R(t) so that, with a voltage drop

of 1/3 V+ across it, the value should be 100 times more, if practical.

So, it should be obvious that the real limit to be placed on C(t) is its leakage,

not it's capacitance value, since larger-value capacitors have higher leakages

as a fact of life. Low-leakage types, like tantalum or NPO, are available and


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preferred for long timing periods.

Sometimes input trigger source conditions can exist that will necessitate some

type of signal conditioning to ensure compatibility with the triggering requirements

of the NE-555.

This can be achieved by adding another capacitor, one or two resistors and a

small signal diode to the input to form a pulse differentiator to shorten the input

trigger pulse to a width less than 10uS (in general, less than T).

Their values and criterion are not critical; the main one is that the width of the

resulting differentiated pulse (after C) should be less than the desired

output pulse for the period of time it is below the 1/3 V+ trigger level.

There are several different types of NE-555 timers manufactured today.

The LM-555 from National was the most common one in the days of late 1996..

The Exar XR-L555 timer is a micropower version of the standard NE-555 offering

a direct, pin-for-pin compatible substitute device with an advantage of a lower

power operation making it ideal for battery and other portable applications etc.

It is capable of operation of a wider range of positive supply voltage from as

low as an incredible 2.7 volt minimum up to 18 volts maximum, Previously 15V !.

At a supply voltage of +5V, the L555 will typically dissipate of about 900 microwatts,

making it ideally suitable for many diverse and innovative battery operated circuits.

The internal schematic of the L555 is very much similar to the standard NE-555

but with additional features like 'current spiking' filtering, lower output drive capability,

higher nodal impedances, and better noise reduction system. A true and positive step forwards.

See at Maxim's ICM-7555, and also at Sanyo's website LC-7555 models are

a low-power, general purpose CMOS design version of the standard NE-555, also

with a direct pin-for-pin compatibility with the regular NE-555.

It's main advantages are very low timing / bias currents, low power-dissipation

operation and an even wider voltage supply range of as low as 2.0 volts to 18 volts.


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At 5 volts the 7555 will dissipate about 400 microwatts, making it also highly suitable

for battery operation. The internal schematic of the 7555 (not shown) is however

totally different from the normal NE-555 version because of the different design process

with cmos technology. It has much higher input impedances than the standard bipolar

transistors used. The cmos version removes essentially any timing component restraints

related to timer bias currents, allowing resistances as high as practical to be used.

This very versatile version should be considered where a wide range of timing is desired,

as well as low power operation and low current sync'ing appears to be important in the

particular design.

A couple years after Intersil, Texas Instruments came

on the market with another cmos variation called the LINCMOS (LINear CMOS) or Turbo 555.

In general, different manufacturers for the cmos 555's reduced the current from

10mA to 100µA while the supply voltage minimum was reduced to about 2 volts,

making it highly ideal type for 3 Volt applications.

The CMOS version is the choice for battery powered circuits, however, on the

negative notes side for the CMOS 555's is the reduced output current, both for

sync and source, This is not really a problem as a FET or a NPN or PNP transistor

can be added as an amplifier or a heavier switching output device if so required.

For a simple comparison, the regular NE-555 can easily deliver a 200mA output

versus between 5mA to 50mA for the 7555.

On the work test bench the regular NE-555 reached a limited output frequency

of 180Khz while the 7555 easily surpassed the 1.1Mhz mark and the TLC555

ceased at about 2.4Mhz. Components used were 1% metal film Resistors and

quality low-leakage capacitors, supply voltage used was 10volt DC regulated

Some of the less desirable properties of the regular NE-555 are high supply

current, high trigger current, double output transitions, and inability to run with


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very low supply voltages.

These problems have been remedied in a collection of CMOS successors.

A word of caution about the regular NE-555 timer chips; the NE-555, along with some

other timer ic's, generates a huge (approx 150mA) supply current glitch during each

output transition. Be very sure to use a hefty bypass capacitor over the power connections

near the timer chip. And even so, the NE-555 may have a tendency to generate double

output transitions.

Basic NE - 555 ASTABLE ( MULTIVIBRATOR ) Operation:

Basic NE-555 Astable (multivibrator) operation:

Figure 9B shows the NE-555 connected as an astable multivibrator. Both the trigger

and threshold inputs ( pins 2 and 6 ) to the two comparators are connected together and to

the external capacitor. The capacitor charges toward the supply voltage through the two

resistors, R1 and R2. The discharge pin ( 7 ) connected to the internal transistor is


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connected to the junction of those two resistors.

When power is first applied to the circuit, the capacitor will be uncharged, therefore, both

the trigger and threshold inputs will be near zero volts (see Fig. 10A). The lower comparator

sets the control flip-flop causing the output to switch high. That also turns off transistor T1.

That allows the capacitor to begin charging through R1 and R2. As soon as the charge on the

capacitor reaches 2/3 of the supply voltage, the upper comparator will trigger causing the

NE-555's internal "flip-flop" to reset.

That causes the output to switch low. Transistor T 1 also conducts. The effect of T 1 conducting

causes resistor R2 to be connected across the external capacitor. Resistor R2 is effectively

connected to ground through internal transistor T1. The result of that is that the capacitor

now begins to discharge through R2.

NE - 556 NE - 558 ICM - 7555 Timer chips

The only major differences between the single NE - 555, the NE - 556 (a dual 555) and a NE - 558 (a quad 555)

are the power rails.Both NE-556 and NE-558 are 14-pin chips) with different pin configurations for power and Ground.

For the other remaining pins it will require you to download from here the PDF for each device from our web site

for further study before using as errors are costly and fried chips (semi's) do not smell too good.

The 8-pin NE-555 Versus the ICM-7555 Note: The CMOS version ICM-7555 by NXP requires studying before using.

It has its own characteristics for power in, power out and over-all power consumption. The ICM-7555 in Astable

or mulitivibrator mode will oscillate up to 500MHz as opposed to the earlier 1971-1979 NE-555's of a mere 200MHz.

It is pin-for-pin compatible, however being a CMOS device, the internal ICM-7555's circuitry differs in many ways.

Most measurements are shown as being in Pico-Amps as opposed to the NE-555 being in Milli-Amps . Therefore,

we strongly urge you to please download the PDF and examine the distinct advatages of either device before using.


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Data Sheet downloads are available here on our web site

At the point where the voltage across the capacitor reaches 1/3 of the supply voltage,

the lower comparator is triggered.

This event causes the control "flip-flop" to set and the resultant output to go high logic.

Transistor T 1 (Fig.3) cuts off and again the result is, the capacitor begins to charge.

This charging and discharging cycle continues to repeat with the capacitor alternately being recharged

and discharged, as the internal two comparators cause the flip-flop to be repeatedly set and reset,

depending on the frequency set by you, the designer of the circuit layout.

The net result is an output that is a continuous stream of nice clean rectangular usable "clock" pulses.

The frequency of operation of the astable circuit is dependent upon the values

of R1, R2, and C. The frequency can be calculated with the following formula:

f = 1/(.693 x C x (R1 + 2 x R2))

The Frequency f is in Hz, R1 and R2 are in ohms, and C is in farads. Typically Micro-Farads (uF) are used.

The time duration between these pulses is known as the 'period' and is usually designated with as 't'.

The pulse is on for t1 seconds, then off for t2 seconds.

The total period (t) is t1 + t2 (see fig. 10).

That time interval is related to the frequency by the familiar relationship:


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f = 1/t or t = 1/f

The time intervals for the on and off portions of the output depend upon the values

of R1 and R2. The ratio of the time duration when the output pulse is high to

the total period is known as the duty-cycle. The duty-cycle can be calculated

with the formula:

D = t1/t = (R1 + R2) / (R1 + 2R2)

You can calculate t1 and t2 times with the formulas below:

t1 = .693(R1+R2)C

t2 = .693 x R2 x C

The NE-555, when connected as shown in Fig. 9b, can produce duty-cycles in the range of

approximately 55 to 95%. A duty-cycle of 80% means that the output pulse is on

or high for 80% of the total period. The duty-cycle can be adjusted by varying the values

of R1 and R2.

Basic NE-555 Applications:

There are literally thousands, maybe 10's of thousands of individually unique ways

that the ubiquitous NE-555 can be used in any or all electronic circuits.

In almost every case, however, the basic circuit is either a one-shot or an astable.

The application usually requires a specific pulse time duration, operation frequency,

and duty-cycle.

Additional components may have to be connected to the NE-555 to interface the device

to external circuits or devices. In the remainder of this experiment, you will build both

the one-shot and astable circuits and learn about some of the different kinds of

applications that can be implemented.


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Basic simple NE - 555 Free sample Circuits:

We have added-in a range of NE-555 circuit samples below for your perusal. Please experiment with them

and have fun, electronics should be fun for everyone. Try ( within reason ) different component values and

use the simple formulas mentioned earlier to calculate your final results. Make only small changes and observe

the results and note your results, do everything in increments. Do not exceed 200KHz oscillation on any NE-555 !

The most important thing to remember:

Note: For correct by-the-book monostable operation with the NE-555 timer, remember the "negative-going" trigger

pulse width should be kept quite short when compared to the required output pulse "width".

Values for the external timing resistor and capacitor can either be determined from the previous formulas.

However, you should stay within the ranges of resistances shown earlier to avoid the use of large value

electrolytic capacitors, since they can tend to be leaky. Tantalum capacitors, low E.S.R. low leakage

electrolytics or mylar types and some brands of monolithic ceramics should always be used.

For +Vcc supply noise "immunity" on most timer circuits we recommend a the simple addition of a ceramic

0.01uF (10nF) capacitor between pin 5 and ground. In all circuit diagrams below we have used the LM-555CN

timer IC from National Semiconductor, but the NE-555 and other brands should not give you any problems.

Now, please bare in mind, the noise on the supply line that is created by a NE-555 operating. It is always good

electronic practice to place fairly large value capacitors, say to the order of 470uF 16V or 1000uF 16 V

when using the NE-555 as we and many other NE-555 users have noted the spurious "dirty" harmonics from most brands

of NE-555 chips. The addition of a 10uF tantalum capacitor, a 470uF electrolytic and a ceramic 0.01uF seems to work.


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FREE NE - 555 CIRCUITS to EXPERIMENT WITH"


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Darkness Detector: Figure 1 (above)

This is indeed an interesting circuit which has the facility to sound an alarm if it

suddenly gets too dark compared to the previous light level.

A simple use for this circuit would be its use to notify someone when a globe

(or light bulb) fails to operate or is open circuit.

The darkness detector uses a regular cadmium-sulphide LDR (Light Dependent Resistor)

to sense the "quick" absence of light falling on the LDR and to operate a small and quite

cheap 8 ohm speaker. The LDR enables the alarm when light falls below a certain level.

Calibration could be effective if a 47K potentiometer was added in series with the LDR.

Power Failure Alarm: Figure 2 (above)


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This circuit can be used as a simple yet effective audible 'Power-Failure Alarm'.

In this cunning application it uses the NE-555 timer as an oscillator biased off

by the presence of line-based DC voltage at Pin 7.

When the line voltage fails (monitored 9V line), the bias is removed, and the alarm tone

will be heard in the piezo-electric speaker. Choose a Piezo around the 105dB mark.

R1 and C1 provide the DC bias that charges capacitor C1 to over 2/3 Vcc voltage, in

this case, about 6.0 V thereby holding the timer output low. Diode D1( 1N4148 / IN914 )

provides DC bias (approx 5.4V) to the timer-supply pin 8 and optionally float-charges a

rechargeable nickel metal hydride 9 volt battery across D2. R4 10 ohms is optional if needed.

When the line power fails,the 9V input via D3, DC is applied to the timer through D2.

resulting in a very audible sound. Experimentation with higher voltages such as 12 V DC

can result in some novel and some interesting educational concepts coming to fruition.


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Fig. 3 Tilt Switch: Figure 3 (above)

This clever NE-555 application is basically an alarm circuit, it displays how to use a NE-555 timer and a simple small

glass mercury switch to indicate an alarm condition, either by forced movement or by the act of tilting a protected item.

The NE-555 is there to serve as a "pseudo-latch", by closing the circuit, the 100K is pulLED "low", pin 2 is sent low

and triggers the NE-555 retaining or "memorising" the last closed circuit state by the closing of the mercury switch.

Resetting is via SW-2. Output "high" from pin 3. drives the base of Q1. Check first your transistor "specs" for base

saturation values and calculations. A 2N2222 should switch well with R3 as1K ~ 1K8 depending of course on the load,

a relay with a 350 ~ 600 ohms coil will suffice. Don't forget a protection diode across the relay pointing to +ve.

As far as we know, there is no other metal which is a liquid at room temperature. Mercury (Hg) is such a metal and has some

unusual and unique properties which are diametrically opposed to the properties of water surface tension and side adhesion.

The mercury switch is carefully inserted into a short 20mm tube of plastic then mounted in its normally 'open' position, in

which this allows the NE-555 timer's "trigger" pin 2 to stay high being fed via R1 100K.

Pin 3 output will stay low, as established by C1 0.1uF on startup acting upon pin 4. When the mercury switch is disturbed

via vibration or movement thus causing its contacts to be bridged momentarily by the liquid mercury, the NE-555 latch is set to a

high output level where it will stay even if the switch is returned to its starting position thus driving the base of Q1 via Rx (R3)

which may be as low as 560 Ohms.

The high output can be used to enable an alarm of the visual or the audible type. Reset switch SW2 will silence the alarm and

reset the latch. Note: Due to the required characteristics of the Vcc +ve turn on, C1 must be ceramic 0.1uF ( 100 nF ) capacitor.


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Photo-Electric Eye Alarm: Figue 4 (above)

The Photo-Electric Eye Alarm is similar circuit like the Darkness Detector of Figure 1.

The same type of Photo-LDR (light dependent resistor) is employed as in Figure 1.

The pitch tone for the speaker can be set and adjusted with the 470K ohm potentiometer.

One of the great ideas here, is to send a beam of light via a tube approximately 30 cm long

with a standard 5 watt bulb (or similar) across a doorway or even a room and use this

beam of light as an alarm, so, when the beam is broken, the NE-555 provides an audible

indication of a "intrusion". This is similar to LED based systems currently in use today.


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The Pocket Metronome: Figure 5 (above)

A Metronome is a one of the most widely used devices in the entertainment and music industry.

With a rhythmic 'toc-toc' sound you can set the tempo of a piece of music to the correct beats per minute,

the speed of which can be adjusted with the VR1 250K potentiometer, providing the desired "beat" or "tempo".

R1 and R2 with C1 form the approximate 50% duty cycle.

A metronome is also a very handy tool if you new to learning to play a music instrument and need to maintain

the correct rhythm as it was intended by the original lyric and rhythm composers on the sheet music or "by ear".

It can be made to fit neatly in a small "Jiffy Box" and as it is powered by a 9 Volt battery, the size can be reduced

to what ever compact size you need. Remember to drill the holes before attempting to mount and adhere your small 8 ohm

speaker with contact adhesive.

Using a sharp scriber, make a circular scribe around the outside of the speaker and then divide the circle into 4 equal

parts then into 8 and using smaller "rings" say... 12mm from the centre, make smaller scribe circles intersecting the 8 lines.

Now, make a larger circle of , say 24mm from the centre and at each of the 8 lines drill your holes. You should now have 17 holes

including the one in the centre.

Drill a series of 4mm ~ 5mm holes in a circular pattern to facilitate the "toc-toc" sound existing the small plastic jiffy-box.

A volume control could be added, but only if required.We suggest a 100 ohm ~ 250 ohm potentiometer after the 10uF C2 capacitor


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C-W Practice Oscillator: Figue 6 (above)

C-W is the abbreviation for Continuous Wave or simply Morse-Code. S.O.S. or dot-dot dash-dash dot-dot .. -- ..

You can utilise this neat circuit to practice the morse-code with this circuit, perhaps to get your amateur (ham) radio license .

Surprisingly enough, morse is the "fall-back" form of communications, that is to say, once all radio communication has gone down

morse signals can still be made using the most primitive of "spark transmitters", even a car coils can be used in the hands of a

person versed in morse code. Dots are a quick noise, dashes are three to four times the width of a dot in morse code.

It is very often used to communicate between submarines (visually by blinking the light from the periscopes) and is still taugh in

all military schools as a back-up communication, just in case modern radios "bite the dust". Very useful communications indeed.

The VR1 150K potentiometer is for the 'pitch' and the 15K is to adjust the speaker's volume.

The "Key" SW2 is a standard morse code key, these are available in most good electronics shops.


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C-W Monitor: Figure 7 (above)

This ingenious little NE-555 circuit monitors the morse code " on-air " via the "tuned circuit" connected

to pin 4 and the short wire 900mm antenna.

The 100K potentiometer controls the tone and pitch.

It is open to a small amount of experimentation for the end user to achieve the best results.

We found it quite fascinating how simple and easy to use it was ased on the circuit details.


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Click this picture for more circuits

12 Minute (760 seconds) Timer: Figure 8 (above)

This neat little circuit can be used as a quiet time-out warning for Ham Radio operators as required by The Australian

Communications Commission (A.C.C.) requires that a Amateur Radio (HAM) operator identify his or her station by giving his

or her call-sign at least every 10 minutes, basically operating under the same rules that govern commercial AM and FM

radio stations. This can present itself as a small challenge, especially when carrying on lengthy intense discussions

as well as in depth conversations resulting in one actually loosing all track of time while "chatting" with another.

A visual indication is used with no "beep", however if you wish, you can add-on a small NE-555 oscillator circuit.


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The NE-555 comes to the rescue in this simple quiet circuit and is used as a one-shot so that a visual warning indicator

becomes active after 10-minutes. You set it for whatever time you wish the NE-555 to take to trigger and change state.

Maybe 10 mins or less, you choose, with the circuit suggested here, you can set the time from 6 seconds to 760 seconds.

It can be further cascaded to a second NE-555 that is setup as a simple "beep" oscillator as in FIGURE 6A .

At the commencement of conversation, turn it on, the red LED will light-up, next remember to the reset switch

which will causes the Green LED to light up. After timing out the green LED extinguishes and the RED LED turns on.

The circuit (Fig.8) shows R2 as 2K2, this circuit can operate still well without the R2 connected. Upon experimentation,

it was found that virtually any value, for instance up to 250K ohms worked without effect and the timing or the operation,

noting that connecting the CRO probe will trigger the NE-555. It was also reveaLED that by hanging a small 30cm (1ft)

insulated wire off pins 2 & 4 "in situ" and connected to pin 2, the mere "close" contact with that insulated

wire triggered the NE-555 to change states. Be aware of the created "sensitivity" to induced "noise" by having the NE-555

configured in this manner. Here in the described circuit we used a 2K2 resistor as that was what was "laying around" at the time.

Operation is simple:

After 10 minutes, set by the 4M7 (4.7M) potentiometer VR1, the 'Red' LED will light to warn the operator that he or she must

identify and , if the circuit in FIGURE 6A is implemented, a short "beep" from an aditional NE-555 oscillator circuit will assist in

sticking to the A.C.C. rules. Using a trusty digital stop watch , adjust VR1 to indicate 10 minutes or as close to it as you can.

Sitting there, waiting for the prescribed 10 minutes or even less to occur is about as boring as watching a small block of ice melt.

We can be well assured that the A.C.C. sits there, highly productively, wasting time just to catch you. Your taxpayer dollars at work?

The A.C.C. rules the waves....the air-waves that is A.K.A. the radio spectrum.

We had absolutely no idea that they actually "own" the air-waves or spectrum. This begs the question, who did they buy them from ?

We are of the firm belief that the air-waves or radio spectrum exists in nature and as such, no one entity can claim ownership of it.

It states on the A.C.A. website from time to time that they are auctioning-off parts of the radio spectrum. Now our simple understanding

of common law is, in order to sell/auction something, you must first and foremost, 100% own the said item that you are selling/auctioning.

That is to state, you hold clear and free legal tile of the said goods. It must not be encumbered or under a caveat of repossession etc.

We guess we must have missed reading the part that states that the Government is exempt and therefore over-rules everyone. Interesting!

This reeks of a certain similarity to the insane scams of people claiming they own the moon and selling off " moon real-estate ",

that of course is a folly in itself, but none-the-less, the Australian Government claims ownership of our radio spectrum, how quaint!

That also begs a further question, just how far do they assert ownership of the spectrum ? Does it stop at the edge of space or what ?

To date, no-one can direct us in the direction of who, when and how the Government became the said owners of a naturally ocurring intangible

item such as a radio spectrum. The spectrum cannot be bottLED, boxed or controlLED by anyone, it exits before Cook and his tourists arrived.

Does the Government have some monopoly over all the area of Australia extending from terrestial earth to a distance out in space?

Curious questions ? Under section 52 of the Trade Practices Act, selling/offering for sale when you do not have 100% ownership is fraud.


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Having asked who did they buy it from and when and how much was paid, these questions were all rejected and we were directed to a PDF.

The said PDF did in no manner state the words "ownership", "payment" or the limit and size of the claimed ownership of this radio spectrum.

Schmitt Trigger: Figure 9 (above)

A very simple, but highly effective circuit. In this circuit, the NE-555 cleans up all noise on the input

signal resulting in a nice clean and "squared signal" output.

Results are immediately realised when used in radio control ( R / C ), as it will clean up noisy

servo signals caused by "RF" interference induced by long servo leads. As long as R1 equals R2,

the NE-555 will automatically be biased for any supply voltage in the 5 to 15 volt (maximum 16V)range.

Please note, that there is a 180-degree phase shift.

This circuit also lends itself to condition 50Hz or 60-Hz sine-wave reference signal taken from a 6.3 volt


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AC transformer before driving a series of binary or divide-by-N counters.

The major advantages are that unlike a typical conventional multivibrator type of squares which divides

the input frequency by 2, this method simply squares the 50Hz or 60-Hz sine wave reference signal

without any division what so ever.

Improved Timing Circuit: Figure 10 (above)

Much more improved stable timing output is achieved with the addition of a single transistor and a diode to the R-C

timing network. The frequency can actually be varied over a wide range while maintaining a constant 50% duty-cycle.

When the output Pin 3 is HIGH, the transistor is biased into saturation by R2 so that the charging current passes

through the transistor and R1 to C. When the output goes LOW, the discharge transistor (pin 7) cuts off the transistor

and discharges the capacitor through R1 and the diode.


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The high & low periods are equal. The value of the capacitor (C) is 100nF (0.1uF) and the resistor " VR1 Potentiometer "

is 2M2 (2.2 Meg Ohms). This is but a mere example of how to configure it , R - C values are entirely dependant on the

type of application, so choose your own values (within reason). The diode can be any generic small signal diode, for

example the 1N4148, or 1N914 can be idealy used however, a high conductance Germanium or Schottky type of diode will

minimise the diode voltage drops in the transistor and diode. (only if that is absolutely necessary for operation)

Having said that, the transistor should have a high beta (gain) so that the R2 1K5 can be larger and

still cause the transistor to saturate. The transistor can be a BC547, BC548, BC549, 2N2222 or similar gain NPN transistors.


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Missing Pulse Detector (A basic simple circuit): Figure 10A (above)

This transistor can be replaced with a BC547, BC549 or 2N2222. This is a very basic example

but does in fact work. Try some small experimentation with the values of R and C.

Be aware that 100 ohms is not the preferred value for R1, it was placed there for

a small incoming signal from a remote control over several hundreds of meters away and

the filtering required for that length of cable has deliberately been left out for simplicity's sake.

The correct value if driven from another source would be determined by the amount of current

and voltage applied to almost saturate the base of Q1 BC548 thus turning it "on" so in theory,

R1 (presently represented as 100 ohms could be 1K or 2K2 or higher ) it is of your own choice.

Briefly, if there is a missing "pulse" to the base input of Q1 BC548 or no signal at all, it sees

it as a missing pulse inverts the signal within the NE-555 and sounds a piezo DC buzzer.


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Hi / Lo or Hee-Haw Tones: FIGURE 11 (above)

This circuit runs two NE-555 timers together to create a "Hi / Lo" tone slightly similar to a "Hee-Haw tone.

The timing is set-up by R1 (12K) and R2 (1M ohm) in conjunction with C1 (0.1uF) 100nF a polycap or ceramic.

One "timer" IC-1 sets the mark-space ratio of "on / off" from its Pin 3 output, feeding to pin 7 of the second NE-555 (IC-2).

The second NE-555 (IC-2) forms a very simple oscillator, you can add this great effect for your childrens toys.

IC-2 forms as a multivibrator, delivering a set of tones provided by the voltages present at pin 7 of IC-2

and the interaction of R4 (390K) and R5 (12K) and C2 (0.01uF or 10nF), the output limited via C3 a 15uF electrolytic capacitor.

Notes:

It is believed that 15uF caps used at the time when the circuit was devised, are no longer made, so it is safe to use 22uF caps.


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Recording Beep: FIGURE 12 (above)

As you may be aware, it is actually highly illegal in this country to record any phone conversation without

the "other party's" full permission. This circuit is used to keep recording of telephone conversations within the

guidelines of being legal. Once you have secured the "other party's" permission to record their conversation, then

this circuit device built in a box is what you will need to have on "standby" the unit "beeps" every 10 seconds.

This will not require interfacing nor connecting to the phone lines as it is a stand-alone 9V unit which fits snugly

within a plastic "Jiffy-Box" (see "Jaycar" or "Altronics") . The law requires you to provide "beeps" every 10 seconds

while you are recording both parties (ie: you and the person you have called ) conversations. No beeps = no recording.

The output of left IC-1 Pin 3 is fed to Pin 1 of the right side NE-555, supplying a ground pin momentarily. This drives

the NE-555 to produce a higher tone while on the high side of the left NE-555's "ON"cycle. The ouput from the right

side (IC-2) NE-555's pin 3 feeds a signal via C3 15uF to the 8 ohm speaker. Any 8-ohm 500mW speaker will do.


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Electronic Decision Maker circuit. Figure 13 (above)

Basically it's a Yes or No decision maker, a novel use of a NE-555 for use when you can't make up your

mind yourself and to have a bit of fun with.

You could also use it as an executive decision maker. To Fire an employee or not to fire them.

The NE-555 is wired as a Astable Oscillator, driving in turn, via pin 3, the 74LS7473 a Dual J - K flip-flop.

It can also be used as a "game" heads or tails whereas, pressing the SW-2 button will result in an either heads or a

tails indication, it's up to you to pick.

Have loads of fun at parties. invent some new fun and exciting games using this simple device.

When you press Sw-2 it randomly selects the 'YES' or 'NO' LED. The LED's flash-rate is about 2KHz (Kilo-Hertz),

which is much faster than your eyes can follow, so initially it appears that both LEDs are 'ON'.

As soon as the switch SW-2 is released, only one LED will be lit. The decision is yours to do with as you please.

Enjoy, have fun with your electronics projects, that's what it's all about!


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1Hz clock Generator

This simple oscillator example uses the NE-555 to output 1 Hz.

The frequency output can be easily calculated by the following formula :

Note: In reality, the output frequency will display on your CRO as 1 Hz, based on the applied maths. The circuit maths

suggests that a 1K pot can be used, however some are found to be 1.013K some are 995 Ohm, so with the error in tolerance of

various parts, it is possible to adjust to the oscillation frequency of 1 Hz with the 1k ohm variable resistor, experiment


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and see what you can observe and discover. The addition of a 100 Ohm resistor in series with VR1 could make all the difference !

Basic NE-555 based Logic Probe: Figure 19A (above)

This logic Probe provides you with three visible indicators:- " Logic 1 " (+, RED LED), " Logic 0 " (-, GREEN LED), and

" Pulse " (YELLOW LED). Please note, at initial turn-on, the yellow "pulse" LED will pulse on / off very briefly.

In the design, the 74LS00N was chosen as it was cheap and it had four two input NAND gates which made it ideal as there were plenty

of "spare gates" to go around and, as a bonus, to employ a NE-555 to use as a "pulse indicator", a sort of "hold and display" chip.

The basic circuit as it is shown above is very good for TTL but not CMOS due to voltages in excess of 5.5 Volts. It will fry above 5.5V.

We may include the CMOS version at a later stage if requested. This will require a re-design of this circuit to comply with CMOS.

The yellow or 'pulse' LED comes on for approximately 190 milli Seconds to indicate a pulse without any regard to its pulse width.

This feature enables one to observe a short-duration pulse that would otherwise not be seen on the logic 1 and 0 LED's.

A small sub-miniature slider switch SW-2 across the R8 22K resistor with a 100 ohm R7 to limit the current to pins 6 and 7 can

be used to keep this "pulse" LED feature on permanent enough after a "pulse" occurs to confirm the existence of the pulse.

In operation, for a logic ' 0 ' input signal, both the ' 0 ' LED and the pulse LED will come 'ON', but the 'pulse' LED will go off after

about 190 mSec. The logic levels are detected via resistor R1 (1K), then amplified by Q1 a NPN, Silicon transistor Q1 set as a

pre-amplifier and driver and selected by the 7400 IC for what they are. Diode D1 is a small signal diode to protect the 74LS7400

and the LEDs from excessive "inverse voltages" during capacitor discharge.


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For a logic ' 1 ' input, only the logic ' 1 ' (red) LED will be 'ON'. With the switch SW-2 closed, the circuit will indicate whether a

negative-going or positive-going pulse has occurred. If the pulse is positive-going, both the ' 0 ' and 'pulse' LED's will be on.

If the pulse is negative-going, the ' 1 ' and 'pulse' LED's will be on.

Basic NE - 555 based Extended timer: Figure 23A (above)

VR1 together with R1 control the pulse rate from the NE-555, C1 10uF set the timing. Output from Pin 3 of IC 1 NE-555 travels to the

clock input of IC 2, HEF4017. Please note: On IC2, IC3 and on IC4 pin 12 is an output referred to as "carry Enable". The resultant

timing is, from IC-1, 10's, from IC-2 100's and from IC-4 1000's in delays. The 4017 sequentially makes 1-of-10 outputs high while

others stay in a "low" state in response to inward clock pulses. Many applications count on the 4017. The actual counting occurs when

pin 13 and 15 are low logic level. Switch SW-2 is used to reset or activate and run the timers. SW-1 switches + 9 Volts power.


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The Basic NE-555 Circuits :

Have fun with electronics with different sounding devices, different indicating devices such as lights, LEDS, noise making devices,

relays. Try different types of LDR's and..remember, if for some reason you get false triggering, connect a ceramic 0.01uF (=10nF)

capacitor between pin 5 ( NE-555 ) and ground as well as 470uF electrolytic capacitor across the suppy near the NE-555 chip's pin 8.

In all circuit diagrams below, we used the LM-555CN timer IC from National Semiconductor. The NE-555 timer will work with any D.C. voltage

between 3.5 and 15 volt. Do not exceed this as it will smoke-up ! A single 9-volt Alkaline battery is usually a good general choice.


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The Basic NE-555 NEON LAMP DRIVER Circuit :

A simple circuit to power a NEON lamp. Primarily it was used to test 90 Volt neons where "tester safety" is a high requirement.

Often in industry, we need to make choices as to what an employeee can and cannot use in full safety in the workplace, this is one such

battery powered device.

The R1 - R2 - C1 circuit determines the output oscillation frequency of the NE-555, thus producing a voltage at Pin 3 just high enough

to power into the small 8 ohm transformer's primary windings, the secondary windings are 1K ohms. Thus testing any 90 Volts neon.

This results in a ratio of about 125 times gain, however we all know based on the maths, that's not going to fly. What about the Losses ???

The "theoretical voltage" of around 500 Volts AC passing through R3 10K dropping to around 180V AC is thus just enough to strike the gas

within the neon and therefore lighting it enough to detect whether the neon is a goer or just a bit of glass. It is not designed for continious

usage but as a "go or no-go tester", easily fitted into a small plastic box, powered by a 9 V battery and very portable. User friendly.


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The Basic NE - 555 Infra-Red Transmitter Circuit and NE - 567 Receiver :

A simple NE - 555 circuit is employed to primarily power an infra-red LED. Virtually any brand of NE-555 may be used here.

The VR1 - R1 - C1 circuit determines the NE - 555 oscillator producing a square wave rise and fall voltage at Pin 3 driving the

Infra - Red LED 1, being fed + Vcc via "R2" with a set value of 10 ohms. The NE-567 is a phased-locked loop chip

Check the data sheets for your infra-red LED as the current requirements will vary from manufacturer to manufacturer. You may need

to increase the "R2" value to 22 ohms or more based on the operation current of the I.R. LED. (see PARTS 9 lines below)

This simple NE - 555 circuit runs on a single + 9 Volt DC power source, we suggest using a power supply for long term deployment.

The circuit is designed for security use where an inconspicious infra-red LED beam is needed. It is open to you for experimentation.

SETTING UP:

Setting up is relatively easy, with power applied to the receiver portion, gently turn VR1 on the Transmitter board until the relay

clicks ( chatters ) and operates fully and becomes as a fully latched-on mode. Be patient, this latching may take up to 2 seconds.

We suggest using a small plastic "tube" perhaps with a small lense on the Photo-Transistor part to direct the incoming infra-red beam

directly into the tube to achieve the best results. Line both the tubes up for best results, this task will require two persons.


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Please experiment with the same "tube" concept on the transmitter end as this will make the devices respond to directional infra-red

input rather than a "splatter" of I.R. waves. Note: operating at lower frequencies affects latching times, making them slower.

PARTS: Infra-red transitor - Wagner Electronics, Part No:IRR53C (clear lens) Infra-Red Diode - CQY-89 (remote control IR diode)

The Basic NE-555 Simple Flasher Circuit :

A simple and novel NE-555 dual globe flasher circuit to primarily power a relay that switches power to each globe in turn.

The R1 - R2 - C1 along with VR1 4K7 combo determines the NE-555 to oscillate slowly producing a voltage at Pin 3

driving the base of Q1 2N2222 an NPN transistor, which in turn drives the relay that switches the two globes on and off.

Diodes D2 and D3 provide the feedback logic 1 pulse to Pin 4 reset of the 555. C2/R4 forms a slight "buffering" function.

This simple NE-555 circuit runs on + 12V DC, the circuit is protected against back E.M.F. (Electro-Motive Force) or the

collapsing coil voltage by diode 1N4004 D1 which is rated at 400 Volts at 1 amp.

The back E.M.F. from some coils measured by us has be witnessed on the C.R.O. to generate upwards and beyond a

350 volts spike !

Applications: This circuit was designed for Security use or Vehicle breakdown dual lamp use where needed. Cop cars ?


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The Basic NE-555 Improved Oscillator Circuit :

A simple NE-555 circuit with a vastly improved oscillation. So simple, why did we not use it before?

It uses only one resistor and one capacitor.

For the purpose of the simplicity in display, we have left off the 0.01uF ceramic capacitor which we would usually

connect from pin 5 to ground.

The circuit draws very little current from the supply, however the frequency of operation will in fact be lower than

a dual resistor circuit as describe in many other circuits.

This lower frequency is mostly due to the fact that the voltage delivered by the output line from Pin 3 is

1.7 Volts less than the supply rails.


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The output is still capable of driving up to 200mA. Don't exceed this.

The R1 x C1 circuit determines the NE-555 to oscillate producing a voltage at Pin 3 which also is

fed back via R1 1K driving the NE-555 chip into almost perfect oscillation.

Observe it on the C.R.O . (Cathode Ray Oscilloscope).

This simple NE-555 circuit runs on +5V to +15V DC. Most circuits run very well at 15V DC all day.

This circuit was designed to use for reasonably good square wave output formations.

The Basic NE-555 SIMPLE TOUCH SWITCH :

This simple application of the NE-555 is "triggered" on pin 2 via Q1 2N2222 NPN transistor

operating the NE-555 in Astable Mode. ( see FIGURE 30A ).

The generated voltage is about 3 Volts less than the supply rail voltage due to Pin 3 rising to

approximately 1.7Volts below the supply rail voltage, add to this the 0.6V loss through the diode.

It is sensitive enough to pick up stray voltages such as static electricity and induce mains radiation


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picked up by our bodies.

It can be improved-on by the addition of a second pad connected to ground which will enhance its operation.

This circuit can (with a little experimentation) be connected to a metal gate or similar and be used to produce

a tone using a second NE-555 circuit such as in a modified version either Figure 1 or Figure 2.

Experiment away, don't let your mind be "walled in" by convention and preceding circuits, always experiment and learn.

The Basic NE - 555 SIMPLE SWITCH DE-BOUNCER :


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This mode of operation is also called MONOSTABLE MODE. The NE-555 can indeed be wired as a monostable. A monostable

has one stable state and that is the OFF state. The "unstable" state is called the "ON" or "HIGH" LOGIC state.

When Pin 2 is triggered by an input pulse, the monostable switches to its temporary or ON state.

It remains in that state for a period of time determined by an R-C network and returns to its stable previous OFF state.

Put simply, the monostable circuit generates a single fixed duration pulse during each time it receives its input trigger pulse.

The monostable circuit can also be called a "ONE-SHOT" due to the single-pulse created. This type of circuit can be used for

many switching applications, activating an external device for a specific length of time.

They can also be used to generate timed delays.

Another desirable use for this type of circuit is to take the brief pulse of a push-button and activate a external device.

We refer to this simply as a "PULSE-EXTENDER".

Another novel use is that it can also be used to clean-up the noisy output of a push-button due to poor contacts or a high

moisture area, this we refer to as SWITCH DE-BOUNCING.

The simple diagram below shows a push-button (on left) connected to a NE-555. When this push-button is pressed, you will

note that a relay has been added to Pin 3 (output) the relay operates for about 5 seconds. The button must be released

before the time-interval has expired otherwise the time is extended, so please note that this is a "limitation" of this simple circuit.


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The Basic NE-555 ASTABLE and MONOSTABE MODES :

FIGURE 30A and also Figure 9b (above) both show the NE-555 connected as an astable multivibrator.

Both the trigger and threshold inputs (pins 2 and 6) to the two comparators are connected together

and to the external capacitor. The capacitor charges toward the supply voltage through the two resistors,

R1 and R2. The discharge pin, (Pin 7) connected to the internal transistor is connected to the junction

of those two resistors.

When power is first applied to the circuit, the capacitor will be uncharged, therefore, both the trigger and

threshold inputs will be near zero volts (see Fig. 10). The lower comparator sets the control flip-flop

causing the output to switch high. That also turns off transistor T1.

That allows the capacitor to begin charging through R1 and R2. As soon as the charge on the capacitor reaches

2/3 of the supply voltage, the upper comparator will trigger causing the flip-flop to reset.

That causes the output to switch low. Transistor T1 also conducts. The effect of T1 conducting causes resistor R2

to be connected across the external capacitor. Resistor R2 is effectively connected to ground through the internal

transistor T1. The result of that is that the capacitor now begins to discharge through R2.


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Check the listing in Table 2. It shows some variations in the NE-555 manufacturing process primarily by two different manufacturers,

National Semiconductor and Signetics Corporation.

Since there are many other NE-555 chip manufacturers we suggest when you build your prototype circuits first using one of these two

well known brands and stick with the particular brand of NE-555 model.

You may wish to specify a certain brand in your own NE-555 "circuit" project and its schematics and for a very good reason, the circuit

functions " better " with one brand than another.

Unless you "really" know what you're doing in a critical timing circuit and of course...some do and some don't, stick with one brand.


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BIG NOTICE - READ NOW - TEMPERATURE RATINGS

The absolute " maximum" ratings (in free air) for NE/SA/SE types are:

+ Vcc, supply voltage: 18V Input voltage (CONT, RESET, THRES, TRIG): Vcc

Output current: 225mA (approx)

Operating free-air temp. range: NE555 :........... 0°C - 70°C

SA555 :........... -40°C - 85°C

SE555 :........... -55°C - 125°C

SE555C :.......... -55°C - 125°C

Storage temperature range: -65°C - 150°C

Case temperature for 60sec. (FK package): 260°C

Please folks, remember that the NE-555 chip does create a certain "noise" on the Vcc supply lines, most applications "can live with"

this undesirable characteristic.

It is however, always wise to use "filtering" capacitors, preferably a 10uF Tantalum added to this a low ESR 100uF electrolytic and as

well a 0.1uF disc ceramic capacitor to assist in "cleaning up" spurious noise generated by the NE - 555 on the supply +ve line.

Connecting an electrolytic capacitor the size of between 100uF and 470uF between +Vcc supply line and ground -Vdd as well as a 10uF Tantalum

and also utilising a 0.1uF disc ceramic just to on the side of caution.

It has been observed that the introduction of a 10uH choke in the "supply in line" does not appear to improve any further after the addition


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of those three capacitors.

The three capacitors it would seem suffice in cleaning up the spurious previously observed "noise" on the +Vcc supply in line.

These three caps will greatly improve the line "condition" with the NE-555 oscillating at higher frequencies, these "noises" can be seen quite

clearly on a good CRO ( Cathode Ray Oscilloscope ). The next generation of Oscilloscopes have Liquid Crystal Screens, so what do we call them?

Interesting name CRO, since there is no Cathode Ray tube used, what do we call a LCD screen CRO?.....a LCDO ? Liq-crys-dis-osc?

NE - 555 Timer - Frequency and Duty Cycle Calculator

Enter values for Resistor R1, Resistor R2, and Capacitor C1 and press the calculate button to solve for positive time interval (T1) and negative time interval (T2).

For example, a 12,000 ohm (12K) resistor (R1) and 150,000 ohm (150K) (R2) and 0.22 uF capacitor will produce output time intervals of 24.698 mS positive (T1)

and 22.869 mS negative (T2).

The frequency will be approximately 20.979 Hz. Please Note: R1 should always be greater than 1K Ohms and C1 should be greater than 0.0005 uF.

Scroll up this page for basic NE-555 information ( pinouts & many interesting NE-555 circuits devised for your interest ).

REMEMBER: Do not run an older 1971 - 1979 NE - 555 in excess of 200KHz, it will eventually smoke-up.

Notes: This only applies to the older NE - 555's smoking-up. The newer 1979 onwards do not have this problem.


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R1 (K Ohms) R2 (K Ohms) x 2 C (MicroFarads)

T1 (Milliseconds) T2 (Milliseconds) Frequency (Kilohertz)

The Ubiquitous NE - 555 Timer Calculator ( above )

Above is an example of how a 1 Hertz (clock) frequency was derived, No pun intended :-)


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Acknowledgement

Portions of this particular web page were extracted from our own

private collection of circuits and experiments since 1979.

Layout is Copyright © 1996 Unitech Electronics Pty. Ltd. ALL RIGHTS RESERVED.

First updated: Copyright © January 28th 1996 - © 2010

( 01 ) Added PDF access references: September 21st 2009

( 02 ) Added 1 Hz Oscillator improved clearer calcs text: March 23rd 2010

( 03 ) Added 1 Hz Oscillator Pic Fig 14 and text: March 23rd 2010

( 04 ) Added NE-555 Calc and pic of 1 Hz Oscillator Pic: March 23rd 2010

( 05 ) Fixed problems in viewing with Internet Explorer it had with the simple HTML. Note..No problems with Firefox : March 25th 2010

( 06 ) Cleaned up html & text for bug in Internet Explorer 7 "weird feature". No problems using Firefox: March 29th 2010

( 07 ) Added a sub menu denoted as FREE NE555 CIRCUITs 18 added so far....12 more to come : April 2nd 2010

( 08 ) Refining slight imperfections in gifs and correcting spelling mistakes: April 4th 2010

( 09 ) Added 38 new "click-on" gadgets to simplify navigation on this page : April 5th 2010

( 10 ) Added NE-556, NE-558 and ICM-7555 PDF datasheets and their "click-on" gadgets: April 7th 2010

( 11 ) Added 7 more "click-on" gadgets to assist in better navigation of this page: April 8th 2010

( 12 ) Fixed HTML conflicts discovered in Internet Explorer but work fine in FireFox: April 8th 2010

( 13 ) Note: Conflicts discovered with "mouse-over", the moving chips halt under FireFox but fails to halt under Internet Explorer: April 8th 2010

( 14 ) Added more Gadgets:- TOP, NE-555 Data PDF and Back to Free circuits to navigate the page better: April 11th 2010


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( 15 ) Added even more Gadgets:- NEXT UP, NEXT DOWN, and tidied up some gifs to navigate around the page better: April 20th 2010

( 16 ) Added more PDF icons to assist in navigating the page better. Added Vero-board for 555 tester: April 22nd 2010

( 17 ) Added CSS-555C PDF icon and its relevant text information and Shrunk Table 1: April 25th 2010

( 18 ) Added Fig 5A NE555 Tester Coloured components overlay and revised VeroBoard colourings: May 16th 2010


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plethora of ne 555 data

Documents