TICKING BOMB USING INFRARED SENSOR

COMPONENTS USED:-1. INFRARED SENSOR2. INFRARED RECIEVER3. IC555 4. NPN TRANSISTOR5. RESISTANCES6. POLARIZED CAPACITOR7. BUZZER

INFRARED SENSORIR Transmitter will always transmit IR light (Infrared), it is not visible to human eyes. Since the transmitter and receiver is being arrange side by side,theoretically, the receiver should not receive any or in most cases, it will receive small amount of infrared emitted by the IR transmitter. The working concept of IR receiver is similar to transistor or LDR (Light Dependent Resistor). Just imagine this. Referring to above diagram, the IR Receiver is like a transistor with the base controlled by the IR light received. When there is no IR light receive, the collector of transistor does not allow current to sink to emitter further to ground of circuit. It is like very high resistance from collector to emitter, blocking current going to ground. In this case, the voltage at SENSOR1 node will be high, near to 5V.When the IR receiver receives more IR light, it changes the resistance at collector and allow more current to sink to ground, and this is similar to low resistance at the lower part of the circuitWe utilize this voltage changes to IR light to know whether there is obstacle or not.

IC555Basically, 555 timer is a highly stable circuit capable of functioning as an accurate time-delay generator and as a free running multivibrator. When used as an oscillator the frequency and duty cycle are accurately controlled by only two external components, a resistor (R) and a capacitor (C). The circuit may be triggered and reset on falling wave forms. A 555 timer has two comparators, which are basically 2 op-amps), an R-S flip-flop, two transistors and a resistive network. Resistive network consists of three equal resistors and acts as a voltage divider. Comparator 1 compares threshold voltage with a reference voltage + 2/3VCCvolts. Comparator 2 compares the trigger voltage with a reference voltage + 1/3 VCCvolts.Output of both the comparators is supplied to the flip-flop. Flip-flop assumes its state according to the output of the two comparators. One of the two transistors is a discharge transistor of which collector is connected to pin7. This transistor saturates or cuts-off according to the output state of the flip-flop. The saturated transistor provides a discharge path to a capacitor connected externally. Base of another transistor is connected to a reset terminal. A pulse applied to this terminal resets the whole timer irrespective of any input.

The 555 timer IC (integrated circuit) is very stable, relatively cheap and reliable. It may be used as monostable or astable.MONOSTABLEAMonostable Circuitproduces one pulse of a set length in response to a trigger input such as a push button. The output of the circuit stays in the low state until there is a trigger input, hence the name "monostable" meaning "one stable state". his type of circuit is ideal for use in a "push to operate" system for a model displayed at exhibitions. A visitor can push a button to start a model's mechanism moving, and the mechanism will automatically switch off after a set time.

Astable mode

AnAstable Circuithas no stable state - hence the name "astable". The output continually switches state between high and low without without any intervention from the user, called a 'square' wave. This type of circuit could be used to give a mechanism intermittent motion by switching a motor on and off at regular intervals. It can also be used to flash lamps and LEDs, and is useful as a 'clock' pulse for other digital ICs and circuits.