We found this circuit in 1964 General Electric documentation. The circuit works with mechanical drive and can be adapted to operate as a didactic shield sensor.
This small regulator with transistors can supply 75 mA currents for charging NiCad rechargeable batteries....
This circuit was found in 80's Popular Electronics. The circuit uses an infrared-sensitive phototransistor...
This circuit was originally published in a 1966 book from Spain. The circuit uses a...