# How do I connect this microphone to an ADC?

I have this component http://docs-europe.electrocomponents.com/webdocs/0f2a/0900766b80f2a57c.pdf. It is not clear to me what type of circuit I need to use to amplify the signal from this microphone and then convert it using an ADC.

I have a few of them, I measured their resistance using my multimeter, they show a resistance of about 1k ohm. On the underside of the microphone there seems to be some sort of SMD component (either resistor or capacitor) that bridges the metal part of the two terminals of the microphone. What purpose could this serve?

• This is present on RS website where I got it from, it is RS Stock No. 724-3134 – quantum231 Sep 22 '15 at 21:06
• That's an electret microphone. Go forth and Google. – WhatRoughBeast Sep 22 '15 at 21:46
• What effect does it having 1k ohm resistance and standard operating voltage of 1.5V imply? – quantum231 Sep 22 '15 at 21:50
• "How did you know that?" The data sheet says "condenser microphone", which is also commonly called electret microphone. The part is an FET. – WhatRoughBeast Sep 22 '15 at 21:54
• I know that I need to use pull up resistor with it and then use a decoupling capacitor so only the AC signal goes into the amplifier. What determines the value of the pull-up resistor and the decoupling capacitor? – quantum231 Sep 22 '15 at 21:55

In circuit below you 've see how to power on a Mic, remove it's DC component through a capacitor, amplify it using an op-amp.

Value of resistors depend on your aplication. In most cases 1M resistor is replaced by a 10K-100K resistor.

Depending on your application you can filter it's output to remove undesired noises.

• Why is the noninverting input having 2.5V applied on it? What is the quiscent output in this case? How does the 1kohm resistance of the mic come into all of this? – quantum231 Sep 26 '15 at 0:16
• If you use single supply, then you need to bias your output with a dc voltage, so you will have all negative and positive part of ac signal in output. If you use dual supply (+VCC, -VCC) you've to connect non-inverting pin of op-amp to GND. – HOPE Sep 26 '15 at 5:05
• What do you mean about 1K ohm resistor? – HOPE Sep 26 '15 at 5:06

The problem with electret microphones is that you need to supply them with a DC voltage supply (a 'phantom' supply). For your microphone, this should be about 1.5 volts, and as constant as possible. A filter is needed to separate the constant voltage and the alternating current due to the sound.

One example I found on the 'net is here, I do not know if it matches your microphone.