We found this circuit in the February 1983 issue of Radio Electronics magazine. The 4-digit circuit is based on dedicated integrated circuits of the time. The power supply is not shown.
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...