Electret Mic to Drive Logic (Clap or Whistle)

Nov 17, 2005 6 Replies
I

What is the easiest way to drive a logic high input pin on a microcontroller with an electret microphone?



I want the microcontroller to be able to detect a clap or whistle or any spike in sound pressure. Sound quality and frequency are not important.



The catch is that the circuit MUST run from a single 3v lithium CR2 battery.



The microcontroller is a 12F675 and it has an ADC, so I could use the ADC if it is not practical to get 2.5v to 5v for a digital input pin. But I think I still need to boost the electret's output for the pin to be able to detect a change.



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J

View in Courier: +3V>-----+-----------+------+-------+ | | | | [3k3] [1M] | | +----+ | | | | | |--+--[0.1µF]--+------|------|+\\ |MIC | | | | >--->Vout | |--+ | [1M]-----+-----------+------+-------+----->GND The 3.3k resistor might have to be changed depending on the mic you use. With no sound into the mic, adjust the 1 meg pot until Vout goes high, (about 1/2 scale) then back off until Vout goes low. Then, with sound into the mic, adjust the pot for the sensitivity you want.
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I

Hi John...

Wow, I really appreciate your post with this circuit! This will work perfectly!

I can't seem to find a TLV3701. TI lists it as obsolete, and I can't find a source at the standard outlets (Mouser, Newark, Jameco, etc.) or on Google. DigiKey lists them, but they don't have the PDIP as a stock item (I can't use SMD at this time).

Is there another device that can be subbed?

Thank you!

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J

TLV3702IP. It\'s a dual, so you\'ll have to spare one comparator. Digi-Key has 136 of them them in stock for $2.25 each.
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I

Hi John...

Excellent! Actually, when I searched for your reference to "TLV3702IP" I found the "TLV3701IP" which is not obsolete! I'm not sure how I missed that one. I have ordered samples from TI.

Is there a way to achieve this functionality with transistors?

Thank you!

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J

At the quiescent supply currents involved, I\'d say "no".
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I

Hi John...

I just found this circuit...do you think this circuit will work?

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Thanks!

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