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 ...

Arduino Uno R3; 5mm LDR; 10K ¼W Resistor; 1K ¼W Resistor; 5mm Red LED ; 5V Piezo-Buzzer ; 9V battery; PIR/IR sensor (see text) Sensor Input. Advertisement. Partner Content. ... (PIR) Sensor. The PIR ...

At one end is an LED and at the other the LDR, ... and with a simple divider circuit a voltage can be read by an Arduino. ... but using another LED as the light sensor. Closeup of the sensor: ...