class 2 basic electronics
TRANSCRIPT
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Whats Included Whats an Electrical Circuit?
Invisible Quantities (V, I, R)
Safety
Basic Components
Resistors, Batteries, Light Emitting Diodes(LEDs), ICs, Voltage Regulator
Ohms & Kirchhoffs Laws
Simple Circuits
Integrating to the Parallel Port (basics only)
Textbook & Web References
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Whats an Electrical Circuit?
Every circuit requires these three things:
Power Source
Load
Conductor
Optionally, a circuit may include a control device such
as a switch
9V
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Three Main Invisible Quantities
Voltage, symbol - V, units - Volts
Provides the push
Current, symbol - I, units - Amperes (Amps)
Flow of Electrons
Amount of Current is dependent on Voltage and
Resistance
Resistance, symbol - R, units - Ohms (S) Limits the amount of current
Represents the load of the circuit
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Safe Levels
Voltage: 30 V
Voltages inside a computer do not exceed 12 V,
except at the power supply and power switch,
which could be at 120 V, depending on computerstyle. Be careful in these areas!
Current: 5 mA (0.005 Amperes)
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Voltage Can Be Provided From
A battery
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Voltage Can Be Provided From
Breadboard (trainer)
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Current
is simply the flow of electrons
Direction depends on convention
Conventional Current Flow (+) to (-)
Electron Current Flow (-) to (+)Electron flow isfrom (-) to (+) (flow ofelectrons)
Conventional flow
is from (+) to (-) (holeflow)
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Resistors Basic Specs
Can be rated by
Resistance (Ohms, S)
Tolerance (% of nominal value)
Power Rating (Watts)
Schematic Symbol
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Resistors Types
Fixed
Variable (Potentiometer, Rheostat)
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Resistors Colour Code
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Resistors Colour Code Example
1st band: orange = 3
2nd band: orange = 3
3rd band: red = 2 (i.e. 102)
4th band: gold = 5%
33 x 102
= 3300 S
= 3.3 kS
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Resistors 5 Band Colour Code
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Resistors Typical Power Ratings
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Ohms Law
R
VI
Current (I) is proportional to Voltage (V)and inversely proportional to Resistance (R)
RIV I
VR
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Ohms Law and Power Formulas
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Kirchhoffs Voltage Law (2)
5 V
3 V
2 V
D0
GND
Parallel Port
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Kirchhoffs Current Law
The current entering a junction must equalthe current leaving the junction
Use in parallel circuits.
4 A1 A 3 A
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Series Circuits
One current path, therefore the current is
the same everywhere
...21 RRRT
Total resistance is the sum of theindividual resistances
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Parallel Circuits (2)
)(
)2(
...111
1
21
21
321
valuesametheif
n
R
onlyif
RR
RRRRR
RT
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Light Emitting Diodes
A type of diode designed toemit light Can be visible or
IR
2 V voltage drop
Typically draws 20 mA (0.020
A)
Schematic Symbol
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A Simple LED Circuit
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Interfacing LEDs to the Parallel Port
D0
D6
D5
D4
D3
D2
D1
D7
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Protecting the Parallel Port
Use a 74LS245 Octal Bus Transceiver toprotect the computer parallel port
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Interfacing a Motor to the Parallel Port
2N3904
TIP31
(A stepper motor would require
more outputs)
D0
M
9V
E
BC
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Integrated Circuits
7400 series typically used for logic gate
experiments
Very susceptible to
voltage variations and
static discharge
Note pin 1 on diagram
Refer to applicable data-
sheet for pinouts
1
7 8
14
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7805 Voltage Regulator
Part of the 78xx series of voltage regulatorsCan be used to convert 9 V to 5 V for digital
circuits
7812 Regulated Power supply design
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7812 Regulated Power supply design