Jetson Nano, M.2 Key E Connector: How to use i2s

Robotics & Edge Computing Jetson & Embedded Systems Jetson Nano
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Hello,

I want to connect four mems microphones (i2s) to the Jetson Nano (with the developer board).
As I found out the board supports only one i2s connection via the 40-pin gpio, where I can connect two of the four microphones.

I just saw, that via the m.2 key e connector I can access another of the i2s lines. That would help to get all four microphones up and running.

My question is: how do I access it, what kind of card/ extension do I need to get the suitable connection for the microphone?

Right now I’m in a planing phase. Until I figured out how to connect all microphones I won’t start building the hardware.

edit: I found the m.2 key e pins for the i2s connection. But my main question remains about a suitable card to get the connections out of the m.2 key e connector.
The pins are here on page 6:

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Hi BroElias,

Would like to understand a bit more on the usecases you are targeting? Is it 4 MIC capture only ? No playback?

As I found out the board supports only one i2s connection via the 40-pin gpio, where I can connect two of the four microphones.

From where this 2 microphones limitation coming per I2S? Tegra I2S can be used in TDM mode to support multiple channels (upto 32channels).

Thanks,
Sharad

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Hi sharadg!

Yes the idea is to use the microphone signals on the board (with python) to calculate things like fft etc. I need the 4 microphones to by (relativly) in sync. I don’t need a hifi quality, a sampling rate of about 16kHz would be sufficent for my task.

As far as I read I can only use 2 microphones per i2s connection.
How would I connect the 4 microphones when using the TDM Mode?

For reference, I have multiple of this microphone laying around:

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Hi BroAlias,

One would would typically need an external Audio codec to support multiple DMICs (PDM interface) via single I2S (or design a TDM MIC Array).

While you are free to design the board as per your needs, one such board (which is available off the shelf) is this one. You could take clues from this.

Thanks,
Sharad

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The respeaker are nice, but have the wrong geometry for my setup.
I will dig deeper into the m.2 key e topic. If I find anything I post it here.

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If you are “Ok” with having two I2S interface solution : Below is the I2S signal pin numbers on M.2 Key E slot.

  **Signal                Pin Number (M.2 Key E)**
  I2S3_SCLK                    8
  I2S3_FS                      10
  I2S3_SDIN                    12
  I2S3_SDOUT                   14

Do you need more info?

Thanks,
Sharad

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Yes that’s what I found. You have any recommendation for a fitting m.2key e card/adapter?
I searched yesterday and found nothing really good.

I will check if I can grab the microphone data with another board and transfer it to the Jetson.

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You will have to design a custom M.2 Key-E board with DMICs or get I2S pins out on the connector (may not be easy).

Could you explain how are you going to connect 2 MICs via single I2S?

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