Electronic Eye

Electronic Eye:

Components Required:

1. Regulator 7805
2. Resistors:  R1=100k ohm, R2= 1k ohm, R3=100 ohm, R4=220 ohm, R5=820 ohm
3. Capacitors: C1=10 micro-farad, C2= 1 micro-farad
4. Diodes: D1, D3, D4= 1N4007
5. LED Diode D2
6. Light dependent resistor LDR
7. Buzzer
8. Transistors Q1 and Q2= BC547

Working:

An electronic eye is a simple circuit which operates the buzzer when a shadow falls on it.  Initially a 9V battery is connected to the diode D1 which is in forward biased condition. This diode protects the circuit form negative voltages by allowing the current to flow in only one direction. A regulator IC 7805 regulates the voltage to 5V at the output. The two capacitors used before and after the regulators eliminate the ripple voltage so a constant voltage can be produced.

Light dependent resistors have resistance in mega ohms when it is placed in dark producing logic high at the output and low resistance when placed in light i.e. logic low at the output. This output is received by op-amp which compares the two inputs and send output to  the two transistors. The first transistor inverts the input and the second transistor drives the buzzer. The buzzer starts ringing when the logic is high and also the LED starts blinking.