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This sensitive sound operated switch can be used with a dynamic microphone insert as above, or be used with an electric (ECM) microphone.
If an ECM is used then R1 (shown dotted) will need to be included. A suitable value would be between 2.2k and 10kohms. The two BC109C transistors form an audio preamp, the gain of which is controlled by the 10k preset. The output is further amplified by a BC182B transistor. To prevent instability the preamp is decoupled with a 100u capacitor and 1k resistor. The audio voltage at the collector of the BC182B is rectified by the two 1N4148 diodes and 4.7u capacitor. This dc voltage will directly drive the BC212B transistor and operate the relay and LED. It should be noted that this circuit does not "latch". The relay and LED operate momentarily in response to audio peaks.
Related Links
Downloads
Sound Operated Switch - Link
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Accurate LC Meter
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60MHz Frequency Meter / Counter
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1Hz - 2MHz XR2206 Function Generator
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BA1404 HI-FI Stereo FM Transmitter
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USB IO Board
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ESR Meter / Capacitance / Inductance / Transistor Tester Kit
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Audiophile Headphone Amplifier Kit
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Arduino Prototype Kit
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200m 4-Channel 433MHz Wireless RF Remote Control
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