Simple infrared detector

The simple infrared detector uses the photoelectric conversion characteristics of infrared diodes to detect infrared radiation within a range of 30cm to 50cm. It can be used to check whether your remote control functions normally, and can also be used as the front end in an infrared receiver circuit.

A gallium arsenide p-n junction diode (IR1) can generate about 100μA of current when exposed to visible or infrared light. The current generated is proportional to the intensity of the irradiated light. In this circuit, diode IR1 detects infrared radiation and generates a corresponding current, which is sent to the low-noise JFET op amp TL072 (IC1) for current/voltage conversion and amplification. The non-inverting input of IC1 is connected to the voltage divider formed by R1 and R2. The high-value resistor R1 and capacitor C1 can stabilize the non-inverting input. R3 is the negative feedback resistor of IC1.

When the power is turned on, LED1 lights up, indicating that the circuit is ready for detection. However, it will gradually go out because R3 draws current from the output terminal. At this time, the circuit enters the standby state, and IC1 outputs a low potential. LED1 does not light up.

Point the remote control at IR1 and press any button on the remote control. If the remote control is normal, an infrared beam will hit the detection diode IR1 and generate a corresponding current. LED1 will start flashing, indicating the presence of infrared light. To prevent IR1 from being disturbed by sunlight, a sunshade can be added around IR1.