This TTL circuit consists of a frequency divider or converter that has values selected by a switch. The circuit is from Radio Electronics from December 1980 and must be powered by a voltage of 5 V.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...