We found this circuit in a publication from the 1980s. Transistors can be replaced by current equivalents. The circuit is for 6 V and the capacitors determine the frequency of the oscillations.
This circuit was found in a 80's Popular Electronics. The sensor can be any phototransistor. The circuit is...
This circuit produces rectangular signals from a sinusoidal input. The circuit uses a unijunction...
This circuit can source 3 to 12 V with currents up to 500 mA depending only on the transformer....