The LDR must be soldered in a way that it can comfortably see ambient light through the Fresnel lens. The tiny microcontroller brain. To be frank, using a microcontroller is probably overkill for most ...

Just after the failure, I leaped into the circuit diagram of HC-SR 501 PIR module and found that one end of the LDR pad is connected to ground (0v),where other end is connected to vcc (+3.3v) through ...