circuit diagram of electric eye for breadboard

---

circuit diagram of electric eye for breadboard

---

circuit diagram of electric eye for breadboard

circuit diagram of electric eye for breadboard

An electric eye is a photodetector used for detecting obstruction of a light beam. An example is the door safety system used on garage door openers that use a light transmitter and receiver at the bottom of the door to prevent closing if there is any obstruction in the way that breaks the light beam. The device does not provide an image; only presence of light is detectable. Visible light may be used, but infrared radiation conceals the operation of the device and typically is used in modern systems. Originally systems used lamps powered by direct current or the power line alternating current frequency, but modern photodetector systems use an infrared light-emitting diode modulated at a few kilohertz, which allows the detector to reject stray light and improves the range, sensitivity and security of the device.

Electronic eye is also called magic eye. As the automation is emerging technology these days, just imagine a door bell that automatically rings when a person visit your home. This also provides security when any person is trying to enter into your home without your permission. Electronic eye is the electronic device that continuously watches if anyone is visiting your home. This article presents the circuit of electronic eye. Before going to know complete details about this circuit, get an idea about Light Activated Switch Circuit using LDR.

This circuit can be divided into two parts. One is the power supply and the other is logic circuit. In the power supply 9v supply is converted to the 5v .The logic circuit operates the buzzer when any shadow falls on it.

Power supply circuit consists of battery, diode, regulators and capacitors. Initially a 9v battery is connected to the diode. Diode used here is a P-N junction diode of 1N4007 series. In this circuit 1N4007 is connected in the forward bias condition .The main purpose of the diode in this circuit is to protect the circuit from negative voltages .There is a chance of connecting battery with reverse polarities which damages the circuit. So P-N junction diode connected in the forward bias allows the current to flow only in one direction and thus the circuit can be protected .There is some voltage drop across the diode. A voltage of 0.7V is dropped across the diode.

A regulator is used for regulating the output voltage of the circuit .The regulator IC used here is 7805.78 represents the series and 05 represents the output voltage .Thus a voltage of 5v is produced at the output of the regulator .Two capacitors are used before and after the regulator .These two capacitors eliminate the ripples .Thus a constant voltage is produced at the output of the regulator, which is applied to the logic circuit.

Also Read the Post: Automatic LED Emergency Light Circuit using LDR

The logic circuit mainly consists of Light Dependent Resistor, transistors,Op-amp IC and a buzzer. A 220KOhm resistor is connected in series to the LDR. Light dependent resistor will have resistance in mega ohms when it is placed in dark. This resistance value will decrease gradually when it is placed in the light. Thus there is a variation in the series resistances. When the LDR is in dark it has high resistance and produces the logic high value at the output .When the LDR is in light, the resistance value of the LDR decreases and at the not gate it gives logic low voltage.

The op-amp IC used is LM 358.This IC compares the two inputs and produces an output which is applied to the transistor. Two transistor are connected to the buzzer from these resistances. The first transistor inverts the input from the op-amp. The second transistor drives the buzzer. The diode is placed for protection.

Buzzer used here is a 5v magnetic buzzer. It has two pin at the output. One pin is connected to the not gate and the other pin is connected to the Light Emitting Diode.LED is used for indication only. When the output from logic gate is high buzzer starts ringing. Led also starts blinking.