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VOX — Voice Operated (Transmit) Relay

Have you ever wondered how a transmitter can go ON automaticity when an operator speaks into the microphone, and then turns OFF automatically when he is finished talking? This project shows you how it can be done.

When you finish wiring, turn the Control fully clock-wise (the Lamp will be ON). Then turn the Control counter clock-wise until the Lamp goes OFF (but no further) and speak into the microphone (Speaker).

The Speaker is used as a dynamic microphone and the Lamp is used to indicate the transmitter is ON. The control Transistor turns ON the Relay which turns ON the Lamp.

Of course, it could turn ON a transmitter (or just about anything else) if you wanted it to. For demonstration purposes we have used the Lamp only as an ON indicator, but you could use it for other functions. For example, if you have a tape recorder with a remote control feature, you can use this circuit to make it come on only when there is something to record. Most cassette recorders have this remote control feature.

If longer or shorter delay times are desired, the 10uF Capacitor may be changed to a higher or lower value. Higher values cause longer delays, and smaller values cause shorter delays. Use the Control to adjust the sensitivity of the circuit.

Note: Too much sensitivity causes the circuit to malfunction with a clicking sound when the Relay is turned OFF.

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