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.
This circuit appears elsewhere on this site, but from different sources. Using the LM3900, we find this...
This interesting source or isolation transformer also allows to vary the output voltage by...
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...