This circuit was found in a 90’s EDN. The components used are still common and the sensors can have their quantity increased. The supply voltage is according to the relay.
Found in General Electric documentation from 1967, this circuit uses an unusual PUT today. The...
Pressing and releasing S, the capacitor C1 charges and discharge slowly through the oscillator...
This circuit has a low level at its output (pin 8) when the input signal has a frequency of 10...