This circuit, with printed circuit board included, is from a Radio Electronics magazine from July 1971. The SCR can be any equivalent of the 106 series.
This simple humidity sensor can be used in rain or leak detectors. The circuit is for 12 V supply,...
This fixed current source uses a Norton LM3900 amplifier. The maximum current depends on the...
This circuit was found in an EDN from the 90s. The circuit employs a double 555 and uses the...