Better mic solution for power constraint application than PDM

[Hossein Kasaei]

Hi,

I want to use a microphone in our application consisting of BLE and some sensors. I need continuous sound recording and sending through BLE. Currently MP34DT05 is the one we are using but this a PDM mic ,and as I understood Nordic chip like nRF52832 doesn't offer low power PDM peripheral and I'm getting the average current consumption of around 2.5mA when this peripheral is running which is mostly due to the HFCLK (mic itself consumes 650uA). Can you suggest me a low power solution I can use with the nRF52832? I've already tested the electret microphone connected to the ADC peripheral and seems not to be a low power solution, and by low I mean mic and the peripheral should not consume more than 1 mA (even lower than 1.5mA is acceptable). Using a separate audio codec IC is also power hungry. How about I2S mics? I've heard Nordic chips have some limitations on high frequency clock generating for these kind of mics, although I don't need high frequency, around 4-8 kHz sampling rate is sufficient. In that case  will I2S microphone provide lower power?

Regards,
Hossein

HW : nRF52832
SW : NCS 2.1.1

[Raoul]

Hi Hossein,

Currently MP34DT05 is the one we are using but this a PDM mic ,and as I understood Nordic chip like nRF52832 doesn't offer low power PDM peripheral and I'm getting the average current consumption of around 2.5mA

Those numbers look about right. From the PS you can see that the PDM + easyDMA consumes around 1.4 mA. I believe the HFCLK consumes around 900 uA.

I inquired internally on the power consumption of our I2S peripheral, but it seems that we don't have data on this. A developer estimated that the consumption would be about the same as with PDM.

They also suggested that the best way for you to proceed is to do tests yourself. Try the 3 methods on a DK, and measure their power consumption. I'm sorry to say that I don't have any better alternative.

Thanks for mentioning your required sampling rate. Have you given any thought to the bit depth that you need? How low quality can you get away with?

Best regards,

Raoul

[Hossein Kasaei]

Hi Raoul,

Raoul said:

Those numbers look about right. From the PS you can see that the PDM + easyDMA consumes around 1.4 mA. I believe the HFCLK consumes around 900 uA.

Thanks for your confirmation.

Raoul said:

Try the 3 methods on a DK, and measure their power consumption. I'm sorry to say that I don't have any better alternative.

Don't mention it! I might test I2S to check the difference in power, but anyway I found that if I'm sending at least 100 bytes through BLE, the power goes high enough that even using different mic doesn't help.

Raoul said:

Have you given any thought to the bit depth that you need? How low quality can you get away with?

We rather to have at least 16 bit resolution and the ADC doesn't offer a good one, That's why I think of PDM and I2S.

[Raoul]

Hi,

I see, thanks. I don't have anything to add in that case. Good luck with testing!

Best regards,

Raoul