This circuit was originally intended to operate with a solar source for experiments. Transistors are general purpose, and the output current is relatively low.
This absolute value amplifier was found in a 90's EDN. Equivalent amplifiers can be used. The...
The frequency of the tone produced by this oscillator depends on the amount of light falling onto...
This analog TV circuit can be used on a small transmitter. The circuit is from an 80's American...