This circuit was found in the March 1992 issue of Radio Electronics magazine. The circuit has several adjustments and uses an operational amplifier. Note the supply voltage.
Using a capacitor as a sensor, this circuit was found in the 1989 Radio Electronics Experimenter magazine....
Using bipolar, FETs and unijunction this long-lasting timer can reach 10 hours with good quality...
This circuit is found in an American documentation from the 80's. The circuit measures the power of...