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Miniature electrets - how to use?

drillbit

Jul 28, 2016
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Hi all
I've successfully used an electret mic to create a clap sensor, like in this circuit. The mic I used was a large-ish thing like in this picture. Everything worked fine.

I bought some electret mics from Amazon and received some much smaller mics than I was expecting (should have checked the dimensions!)

I tracked down a data sheet which seems like the right one, and it seems to require them to be wired up the same as the larger mic. But when I try to amplify it with transistors - like in the clap sensor schematic - the signal seems to just become flat.

I don't really understand how to read the facts and figures in the data sheet, which might help me understand what I might need to do differently.

Can anyone help me understand either how to use these things, or how to read the datasheet to design a successful amplifier to trigger a 555?

Thanks
 

Sunnysky

Jul 15, 2016
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You can use CMOS HEX inverter's as an audio amplifier then with diodes, a peak detector, a Schmitt Trigger and a one shot all in one chip or use an Op Amp, transistor and a 555.

But the electret specs say the operating voltage is 2V drawing 0.5mA max from external pull-up Rs. The audio is then capacitor coupled out ( AC) to your amplifier.
So subtract 2V from your clean power source , divide by 0.5mA and that is the value for Rs.
(Vbat-2V)/0.5mA=Rs
e.g. (12V-2)/0.5mA= 20k or nearest value.
e.g. (9V-2)/0.5mA)=14k
upload_2016-7-31_9-37-23.png
An old link of mine can be simplified without pots, but if you breadboard and want to experiment with a 9V battery
http://www.electro-tech-online.com/threads/simple-led-circuit.145396/#post-1228906 Just remember to add the 14K pullup to your mic. to 9V.

The dotted line above contains all the parts inside the mic. and the outside is V- or ground.
 

drillbit

Jul 28, 2016
5
Joined
Jul 28, 2016
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Thanks SunnySky - that helped a lot. I can now see a voltage forming on my oscilloscope when I wire it up with the resistor. Problem is, I want to amplify it with transistors like in the circuit I linked to, but having no luck.

I really struggle with designing transistor amplifiers. Is there any chance you could help me understand how to design the transistor stages to get the mic signal amplified to provide a logic high?

I have tried to connect the output from the mic to a transistor - schematic below. That does light up an LED when I blow on the mic, but it doesn't amplify enough to light it up just from a clap.

I tried adding a second stage - schematic below - but this just lights up the LED permanently.

Can you advise me what I am doing wrong with this approach, and maybe help me work out a design which will light the LED triggered by a clap?

Thanks
PS. Couldn't see the link you meant. It opens a thread but I don't see your name anywhere...?
 

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Sunnysky

Jul 15, 2016
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Mono-preamp-based-on-CMOS-IC.jpg
audio-peak-indicator_orig.gif



http://www.talkingelectronics.com/p...ier/TheTransistorAmplifier-P1.html#Connecting
 
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