It only took a few components to accomplish the task. [Justin] uses a pair of NPN transistors triggered by a photoresistor. One transistor is responsible for switching on the buzzer, the other ...

b: The on-off ratios (the ratio of conductivity with/without pseudo-sunlight) of the photoresistor devices. The higher the on-off ratio, the better the performance of the photoresistor.

[Fjord Carver] brings together an RGB LED and CdS Photoresistor to make a color sensor. Those Cadmium Sulfide lights sensors usually have a very wide swing of resistance when exposed to varying ...