I'm trying to make a simple microphone circuit using this microphone: http://www.cui.com/product/resource/cma-4544pf-w.pdf

I am connecting a 3V supply to a 2.2k Ohm resistor which then leads to terminal 1 of the microphone. I have terminal 2 of the microphone going to ground. I have terminal 1 of the microphone also connected to a 1uF DC blocking capacitor with the negative terminal of the capacitor being the terminal connected to the microphone.

I am then attempting to use a Tektronix DPO 4034 Oscilloscope to measure the output of the microphone by probing the positive side of the 1uF capacitor which has been left open.

When I do this, the oscilloscope is only showing the ambient static the probe is picking up. The signal on the oscilloscope does no change if the microphone has 3V power or not.

What can I do to be able to measure the output of the microphone?

  • \$\begingroup\$ "I am connecting a 3V supply to a 2.2k Ohm res...", you can turn these words into a schematic. - "I am then attempting to use a Tektro.....", this should definitely be shown in a schematic. Some people measure current by putting it in parallel with what they are trying to measure. \$\endgroup\$ – Harry Svensson Dec 2 '17 at 22:39

To get something more than a couple of millivolts from the mic, you must have nearly deafening sound level at the mic. That means loud shouting from distance about five centimeters or less. Then you can get something like 100mV. If your oscilloscope can show 1mV/DIV then you can see something else than a blank horizontal line when one speaks using normal voice and the distance is 50cm. If you have normal 1 MegOhm oscilloscope input, it's no use to increase the capacitance from 1uF to 100uF.

If you need the available audio signal voltage from some weak sounds, you need a preamp. It unfortunately amplifies also the noise of mic's own electronics.

NOTE: This microphone is a low quality device. It's simply useless if you want to make low noise recordings of weak sounds such as non-shouting human speaking from several meters.

| improve this answer | |
  • \$\begingroup\$ If I were to wire the output of the microphone to a standard microphone jack and run it to my computer, could I use a program like audacity to record audio from the microphone? \$\endgroup\$ – Zearia Dec 2 '17 at 23:19
  • \$\begingroup\$ @Zearia. Yes if your soundcard records millivolt level signals. For example I have a soudcard that needs several hundreds of millivolts for full level input. For it this mic is useless without a preamp which has voltage gain at least say 30. Check, if your soundcard has an in-built mic preamp or level boost available. As I told, do not expect low noise when recording weak sounds. Speak from distances 0,5m or less can be ok. \$\endgroup\$ – user287001 Dec 2 '17 at 23:28
  • \$\begingroup\$ Would it be possible to amplify the signal using an PNP 2N4403 BJT transistor? I happen to have one on hand. Would a simple common collector configuration work? \$\endgroup\$ – Zearia Dec 2 '17 at 23:32
  • \$\begingroup\$ @Zearia you can try common emmitter amplifier. Common collector amp do not provide voltage gain. an example: 78.media.tumblr.com/tumblr_lpmxdoQVUx1qf00w4.gif The component values probably aren't optimal. Even the voltage must be reverse because 2N4403 is PNP. Single transistor amp isn't low noise nor low distortion. \$\endgroup\$ – user287001 Dec 2 '17 at 23:43

Since you didn't put a schematic, I added one for you. I couldn't add a schematic in comments. Please verify if your circuit is connected like this. If isn't, it should be. The oscilloscope have to be connected to the ground of the circuit. And put a larger cap.

Also, try to change the oscilloscope range. There's no much more to say you post did'n describe exactly what the ranges you were using. I hope it works. Good luck.


simulate this circuit – Schematic created using CircuitLab

| improve this answer | |
  • \$\begingroup\$ This is indeed how I am wiring my circuit. I will try a larger capacitor and return with the result. \$\endgroup\$ – Zearia Dec 2 '17 at 22:43
  • \$\begingroup\$ Increasing the capacitance did not solve the issue. I am beginning to think my o-scope simply does not have the capability to sense the output voltage. \$\endgroup\$ – Zearia Dec 2 '17 at 23:22
  • \$\begingroup\$ measure across the mic. ... you can test your scope by connecting 1MΩ and 1KΩ in series. connect battery across the two resistors. scope probes across the 1K resistor. should measure about 3mV with a 3V battery. use a switch or a wire to intermittently short out the 1K resistor so that you see a waveform on the scope \$\endgroup\$ – jsotola Dec 3 '17 at 21:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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