Found in a Hands-On Electronics from the 90s, this circuit produces the dial tones of an old telephone. The integrated circuit used is uncommon today.
This circuit fires by burning the fuse when the input voltage exceeds the value referenced by the zener....
The UAA180 integrated circuit is no longer manufactured, but if the reader finds one in a scrap...
We find this circuit in a Radio Electronics of July 1984. It consists of the traditional version of 1 A...