This circuit is from a Radio Electronics from July 1965. The circuit uses components from the time also controlling a servo from the time. The power supply is 28 V.
This simple 555 biofeedback circuit was found in the December 1983 issue of Radio Electronics...
This circuit has a programmable alarm that can be triggered with different water levels. The...
Found in a 1991 Hobbyst Handbook, this circuit monitors both battery and alternator voltage. The set...