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Sound-Controlled Relay (UA741)

2014-12-08 00:52  
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This article describes a Sound-Controlled Relay (UA741). The content is very simple, very helpful. Components in this article can help you understand better understanding of this article. For example, in this article, you can go to find and buy these components:UA741.

This is a relay circuit that detect the presence of sound to activate the relay. You can use this sound-controlled relay as voice operated switch, light control, toys, or any other application that can be controlled by a switch. Just replace the switch with? this relay and now you have a sound-controlled device. This circuit uses a 741 operational amplifier to amplify the signal form microphone? with the gain about 100 times. This circuit must use a dynamic circuit, or an electret microphone which has a battery inside. A condenser microphone can’t be used since this circuit has no biasing circuitry. Here is the schematic diagram of the circuit:

Sound Activated Relay circuit schematic

After the signal from microphone is amplified, a rectifier-doubler circuit built with D1 and D2 convert the AC signal to DC. After rectified, the AC ripple is filtered by C4 capacitor to smooth the signal. Finally, a potentiometer R5 is used to adjust the sensitivity of this circuit, calibrating the point? of how loud the sound would turn on the relay.


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