This circuit that uses potentiometer tuning, was found in a documentation from the 80's. The integrated circuit used is from that time and is a not common today.
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....