This circuit is intended for detecting 3 levels power grid voltage, and it can be adapted to operate with the most diverse voltages. The circuit uses neon indicator lamps.
This circuit detects the presence of a pilot flame in heating systems by the presence of infrared...
In the figure we have a circuit that uses unusual components, being indicated for low frequency...
Found in older Signetics documentation, this circuit generates signals from 30 Hz to 25 kHz....