IR-Detection Circuit

The first stage of the circuit involves an IR LED emitting a constant beam of IR light. When a hand or other object crosses this beam, some IR light is reflected back to the circuit. This reflection is detected by the photodiode D2 which results in a voltage drop across D2.





However, we do not want to react to a level of IR detection but instead react to a change in IR signal (i.e., motion) and so a

However, we do not want to react to a level of IR detection but instead react to a change in IR signal (i.e., motion) and so a capacitor (C2) is used to remove and DC offset.



This DC offset is then amplified by U1A and the amplification factor can be adjusted with RV1. This amplified signal is further coupled with U1B which is configured as a Schmitt trigger such that only large detections are allowed to trigger the system.