Detect light thank to a photo-resistor (CDs)
Photosensitive cells (photo-resistor or CdS) are small light sensors.
The resistance drops when the sensitive part (located on top of the photo resistor) is exposed to more light. When illuminated, the resistance is approximately 5 to 10 KOhms. When in a dark environment, the resistance increases up to 200 KOhms.
To use it, connect one pin of the photo-resistance (any, the sensor is symmetrical) to the power supply (Eg: 5V) and the other to an analog input of the microcontroller. Then connect a 10K pull-down resistor between the analog input and ground (GND).
The voltage on the analog input is 2.5V or higher when illuminated and close to ground when placed in the dark..
- A 10 kOhm pull-down-resistor (Brown, Black, Orange)
- Pin length: ~35mm
- diameter: 5mm
- Height: 2.09mm
- Spacing: 2.5mm
- Weight: 0.25g