Sound Operated Switch
Notes:
This sensitive sound operated switch can be used with a dynamic microphone
insert as above, or be used with an electret (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 transitors 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.
Title: Sound Operated Switch
electronic circuit
Source: www.electronics-lab.com
Published on: 2005-02-10
Reads: 1035
Print version: 
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