This circuit was found in the Electronics Experimenter Handbook from 1991. The sensor is a diode and the circuit has a relay according to the voltage used in the supply.
This low-pass filter with 741 op and symmetrical source was found in the August 1993 issue of...
The duty cycle of a Schmitt Oscillator can be programmed by R1 and R2 in this circuit. The...
This circuit is used to test capacitors with a working voltage above 150 V, detecting shorts or...