Electric eye is an old-fashioned term for a photodetector, an electronic circuit activated by light. First developed [1] in the 1890s, this concept has been adapted to new devices and technology and is still in use in the 21st century. Common applications include figure1 shows below remote controls, automatic doors, and motion detectors.

Figure1: Electronic Eye Circuit

This particular term has gradually faded from use at the end of the 20th century, although it was revived in 2009 to describe advances in artificial sight.

Electronic eye circuit uses a photodetector for detecting the presence of a light. Then according to the intensity of light this [2] device turns ON the light when it becomes dark and vice versa.

Since the device is capable of working automatically, this eliminates the need of manual switching of the device and hence saves the manpower. In our electronic eye circuit, we have used light dependent resistor (LDR) to detect the presence of light that falls on the circuit.

The main principle of the circuit is to ring the doorbell when there is any person at the entrance. In order to detect a person, an [3] LDR is used as the sensor. Light on the LDR determines whether a person is present or not. When there is any object at the entrance, LDR is in dark and buzzer starts ringing and the LED starts glowing.

The logic circuit mainly consists of Light Dependent Resistor, transistors, a buzzer, an LED and a few passive components. A 100KΩ resistor is connected in series to the LDR in a voltage divider fashion. Light dependent resistor will have resistance in mega ohms when it is placed in the 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 output it gives logic low voltage.

The circuit of the electronic eye security control system is separated into two parts such as a logic circuit and power supply. The power supply circuit is designed with a battery, capacitors, P-N junction diode and [4] regulators. Here diode is connected in forwarding bias mode and it protects the circuit from negative voltages. When the battery is connected in reverse polarity, there is a chance of circuit damage. So the diode is connected in the forward bias, which allows the flow of current in only one direction. The voltage across the diode is 0.7V.

A voltage regulator (IC 7805) is used to regulate the o/p voltage of the circuit. Here 05 denotes the o/p voltage and 78 denotes the series. Thus 5 volts is generated at the o/p of the voltage regulator. To eliminate the ripples two capacitors are connected before and after of the voltage regulator. Thus the voltage which is generated from the voltage regulator is applied to the logic circuit.

References:

1. https://www.wise-geek.com/what-is-an-electric-eye.htm
2. https://www.electricaltechnology.org/2019/07/electronic-eye-circuit.html#:~:text=Electronic%20eye%20is%20generally%20a%20photoresistor%20that%20turns, light%20beam%20strikes%20the%20surface%20of%20the%20LDR.
3. https://www.electronicshub.org/electronic-eye-controlled-security-system/
4. https://www.elprocus.com/electronic-eye-controlled-security-system/

Cite this article:

Nandhinidwaraka. S (2021) Features of Electronic Eye Circuit, Anatechmaz, pp. 39