This sensitive bio-monitoring circuit was found in the December 1984 issue of Radio Electronics magazine. The circuit is powered by a 9 V battery and uses a low-impedance headphone output.
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...
We found this circuit in a Radio Electronics from January 1967. The SCR is already the C106, which...
This power source with silicon diodes at a time when valves were still used was found in Radio...