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Connecting Microphone to PIC's ADC

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electroRF

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Hi,
I've got earphones and I wanna take its Mic off and connect it to my PIC18F4520's ADC.

Which of the lines do I connect to the PIC's ADC?

The component which is connected by lines #3,#4 to the switch, is the Microphone itself?

(So I should connect Lines #4 to the ADC and Line #3 to the PIC's Ground?)

Thank you very much.

**broken link removed**
 
no idea! but have you measured the output from the mic with a DMM? i think you might need too boost it with a opamp before connecting to ADC but i am not sure, give your way a go tho as i cant see you doing any damage
 
hi LG

I'm trying to figure out how to connect if first and how it works, before measuring it and connecting it to my ADC via Opamp
 
(So I should connect Lines #4 to the ADC and Line #3 to the PIC's Ground?)
The short answer is yes.

The long answer is that the microphone you have there in an electret type and will need an excitation supply.
Just off the top of my head I cannot draw a suitable circuit, but a search here on ETO and the internet in general will provide loads of infromation.

Also, as LG suggests you will need to amplify the output of the microphone to give a usefull signal level for use with a PIC ADC.

JimB
 
The elecret mic uses about 0.5mA. It can be powered from a 10k resistor connected to filtered 9V or powered from a 4.7k resistor connected to filtered 5V.
Its output averages about 10mV (0.01V) RMS when you talk to it about 10cm to 20cm away.

If you want the ADC to process its output level then it must be amplified by a preamp then rectified into fluctuating DC.

10mV RMS is 14.1mV peak. For it to be 5V peak for maximum level of the ADC then the gain of the preamp must be 5V/14.1mV= 355 times.
A volume control can reduce the level if it is too high. An active rectifier circuit can convert it to fluctuating DC.
 
Thank you very much mates!

how do you tell which of the mic's ports is the ground, and which should be connected to the DC?

220px-Electret_condenser_microphone_capsules.jpg
 
I found the value of the resistor to the supply makes a big difference in o/p, 22k is what I used last time.
If you use the internal vref at its lowest setting you might get some sort of usuable values, however you'd be better using a transistor or 741 (wait for it) op amp to make the mic signal louder before the a/d.
 
I found the value of the resistor to the supply makes a big difference in o/p, 22k is what I used last time.
If you use the internal vref at its lowest setting you might get some sort of usuable values, however you'd be better using a transistor or 741 (wait for it) op amp to make the mic signal louder before the a/d.
With a high value resistor and a low voltage for it then the current in the Jfet in the electret mic will severely distort when the sound is fairly loud.

DO NOT use a 45 years old lousy old 741 opamp for audio because its hiss level is much too high.
 
or use a 30f pic with 12 bit ADC :D
 
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