This circuit, which uses a quadruple comparator, was found in old American documentation. The response curve is shown next to the diagram and can be adjusted in the trimpots.
This circuit is from an American publication from the 60's. The power is on the order of 600 mW....
Other operational amplifiers series, such as the MC34072, MC34074, MC35071, MC35072, MC35074 d...
Found in a European magazine from the 90s, this circuit emits beeps that are several seconds apart to...