This simple circuit, found in American documentation, uses only one relay that locks when any of the sensors is activated. To reset, simply turn off the power for a moment.
This circuit is from a publication from the 50's. Inductive components are critical, and...
This simple two-transistor circuit used transistors from the 60s, having been found in a...
This circuit uses an oscillator that generates a signal of approximately 1450 kHz to test...