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Topic: Electret Microphone + LM386 OpAmp + Arduino not working! Please help! :( (Read 2353 times) previous topic - next topic

shubhamgandhi

I followed the mic + op-Amp part of this schematic exactly using an Lm386 chip: https://randomskk.net/projects/lightstrip/schematic.pdf

and sent the output from the op-amp into a pin on an Arduino Pro Mini. BUT, when do an analogRead(pin) and print the value in the serial monitor, the value seems to level out to some constant, no matter how much noise I make into the mic!

Can someone tell me what I could be doing wrong?

As extra information: I left out the capacitor on pin 7 of the IC that is shown in the schematic.
And the power supply I'm using is my old phone charger that plugs into the wall and outputs 5.9V DC.
I am trying to make this:
http://www.youtube.com/watch?v=Km6ObG_xKm4

Also, how do you tell the anode and cathode on an electret microphone? (I tried both ways)

Thanks!

shubhamgandhi

What chip would you recommend?
I will try sending output to a speaker when I get home and get back to you.
Sorry, I posted this at work. I will post pics/data when I get home.
Yes the power supply works properly, I hooked it up to a green LED and it turned on (5.9V was a little too much for itso it permanently changed color haha)

Oh no! Mic fried? Are you positive you can fry an electret mic by hooking it up backwards?

DimKo


Can someone tell me what I could be doing wrong?

Double-check all the wiring, the polarity of the electrolytic capacitors and whether the IC is properly placed (i.e. pin 1 is where you expect it to be)
Then, as KE7GKP suggested, you can connect an alternative audio source at the input and / or use a small speaker at the output. Note: Do NOT connect a speaker or a headphone directly to the output (pin 5) - you need to add an output coupling capacitor there.

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As extra information: I left out the capacitor on pin 7 of the IC that is shown in the schematic.

This is probably fine, but you can always try adding it back to see if that helps :-) The capacitor value does not have to match exactly the one in the schematic.

Quote
Also, how do you tell the anode and cathode on an electret microphone? (I tried both ways)

One of the leads of the microphone should be connected to the outer shell. This is the negative one (goes to ground).

I've had my share of troubles with a similar LM386 setup and have put my build-notes at http://lowvoltage.wordpress.com/lm386-mic-amp/

--
Dimitar
--  Dimitar Kovachev  --  http://lowvoltage.wordpress.com

shubhamgandhi

Hey guys thanks for the help, but I figured out my problem:
I was using the opamp to amplify the signal 1000x which is way past its ability
So I did it in 2 states of 30 each giving me 30x30 = 900 amplification which worked perfectly!

DimKo

Have to disagree. The capacitor from pin 7 to ground is a "bypass" one - it's good to have it in place, but in no way critical. Gain is set by the capacitor between pins 1 and 8.
http://www.national.com/ds/LM/LM386.pdf
--  Dimitar Kovachev  --  http://lowvoltage.wordpress.com

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