Visible and Infrared Light Detection

Abstract

A circuit is made to detect either visible or infrared light. It is designed by using different light detectors, such as, infrared phototransistor, visible phototransistor, and photoresistor. If no light is shining on the detector in the circuit, the green LED is flashing. When the light is shining on the detector, the red LED starts flashing instead of the green one. Op-amp LMC 6482 builds up a simple voltage follower which supplied lower voltage DC power in the circuit. Again, LMC 6482 is the comparator and BS170 is the buffer. When light is off, the comparator buffer output is low, thus red LED is off. However, the oscillator output makes the green LED flashing. When the light is on, the comparator buffer output is high (9 V), thus the square wave signal is transmitted to the red LED, which starts flashing then. In addition, because of LED is a diode, which can only work in one direction, the green LED is off when comparator buffer output is high.

Keywords: – Photoresistor, phototransistor, comparator, LED, voltage, oscillator, electric current