Circuit detectors and sensors based electronics projects

Using this circuit diagram can be designed a nine channel sensor electronic switch using CMOS components.

A simple indicator with buzzer that can be used to warn you if you forget your vehicle lights on, can be designed using this electronic scheme.

Using the PID20 circuit, manufactured by Siemens (which converts thermal radiation into electrical impulses), an operational amplifier and a few electronic components can be made very simple infrared detector.
Size of the output signal of PID20 is determined by the task at pins 3 and 4.