I want to use a CMC-5042PF-AC microphone (datasheet: http://www.cui.com/product/resource/digikeypdf/cmc-5042pf-ac.pdf) to send the type of audio signal a component would expect on an RCA line (line level I am guessing). It's going to go to a wireless video/audio transmitter, which would normally except a line level signal form an audio source such as a security camera.

Here is the schematic for the mic:

Mic Schematic

I am connecting it to 5V power. From what I understand, the R1 resistor would determine the sound level, so I can play around with that to figure out what works best. But what about the capacitor? I can't find in the datasheet what kind of capacitor to use. I have seen people in other schematics use a 1uF cap. Is that what I should do? Or is there a formula I need to use to figure out the cap I need. Also, does it matter if it's a ceramic cap?

Thanks for any hints.

  • \$\begingroup\$ It's just the normal RC frequency formula. \$\endgroup\$ May 3, 2016 at 4:03
  • \$\begingroup\$ The datasheet suggests values. Look right under the circuit diagram. \$\endgroup\$
    – Stephen305
    May 4, 2020 at 21:25

2 Answers 2


R1 (RL in your circuit) determines the microphone gain and the output impedance of the microphone. Basically the output impedance is RL. If RL is (say) 2k2 then the amplifier that C connects ought to have an input impedance (resistance) => 22k. If it is 22k then C and the 22k form a high pass filter limiting the low frequencies and, at a frequency of \$\dfrac{1}{2\pi RC}\$, lower frequencies progressively attenuate more and more.

For 1uF and 22k the frequency is 7.23 Hz i.e. OK for audio - frequencies lower than this will get progressively more attenuated. A 100 nF capacitor would be fine when using the microphone for speech because the cut-off frequency would be 72 Hz.

I'd use a ceramic capacitor - probably X7R type.


Thanks to the comment I found a calculator online:


It uses RC frequency formula to calculate the optimal cap based on impedance and frequency. In my case it was 4.7uF.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.