This circuit lets through the 300 Hz to 3kHz range that corresponds to the human voice. We found it in the Radio Electronics magazine of February 1990. The circuit uses both parts of the LM381.
We found this transmitter in 1980s documentation. Coil data is found next to the diagram and...
The circuit shown here produces a pure square tone of 440 Hz that is suitable for musical...
This circuit, which may have more inputs, consists of an optical OR gate using common...