This circuit is from a 1968 documentation using one of the first integrated circuits available at the time, the TAA370. The circuit is powered by 1.3 V using a 200 ohm handset.
This is one of many circuits of this type that can be found in this section. This one is taken from...
This circuit uses one UJT (Unijunction Transistor) to produce three different tones in a...
This bench circuit was found in the February 1998 issue of Electronics Now magazine. It can be...