Recommended Circuit for Connecting an Electret Microphone to NI 9234

[TmrK]

Hi,

I want to use NI 9234 that I own to do some acoustic signal processing experiments. I understand that there are some microphone+preamp solutions that NI recommends from well-established brands. However, these are usually very expensive (~ $1000-2000) and I was wondering whether it would be possible to use some existing cheap electret microphone capsules with NI 9234 DAQ.

I want to use NI 9234 DAQ with a standard electret capsule that has the following electrical characteristics:

2V standard operating voltage (10V max) and 0.5 mA current consumption with a recommended load resistor of 2.2kOhms.

(Sensitivity: -38dB ±3dB @ 94dB SPL and SNR: 58 dB)

NI 9234 datasheet specifies the following:

Common-mode voltage range: +/-2V, IEPE excitation current 2mA and  IEPE excitation voltage: 19V max.

I have come across few preamplifier solutions online; but they don't seem to be compatible with NI 9234's current supply levels.

Are there any available packaged solutions (something like this one)  that I can purchase that NI recommends for use with 9234 DAQ?

If that is not possible, I would still like to get a recommendation for a simple circuit design that can be used to connect 9234 DAQ to the aforementioned standard electret capsule.

Best regards,

T

[santo_13]

I don't think there is any recommended circuit by NI but you can try this TI reference design - https://www.ti.com/lit/ug/tidu765/tidu765.pdf

[algarcia · Accepted solution]

Hi TmrK,

The internal current source on the NI 9234 is for biasing IEPE sensors. 19V spec is the compliance voltage for the internal current source.

For an electret mic, you're providing the bias and setting gain with the an external 2-10V operating voltage and the 2.2kohm resistor. So in your case you'd be using NI 9234 with the IEPE current source off and AC coupling on (or with an external DC blocking cap).

As Santhosh recommended there are reference designs for electret mic pres, you'll just need to keep in mind the expected mic output voltage for the signals you're measuring and the input range/noise specifications of the NI 9234 to help you determine how much gain your preamp needs to provide.