Help me get a PDM mic working on a custom board Arduino Zero clone, possible a pin/sercom mapping issue...

Official Hardware Classic Zero
1

Hey fellas, I have a MEMS PDM microphone correctly soldered on the right pins, but data always comes back as "0" when using the Adafruit PDM library with their example code. My board has a SAMD21E17 and I'm using Mattairtech's bootloader configured as so. The basic arduino functionality works fine - usb detection & programming, blinking led, fastled etc...

Judging by the multiplex info in the spec sheet, only a few pins are I2S/PDM compatible, but the pair I picked seems correct - 10 for clock and 7 for data, also used in this example. The difference I'm aware of, is that on Matt's board (unlike on a genuine Arduino Zero) the pins are numbered the same. 10 is actually 10, 7 is actually 7 etc... There's probably more to it though, I kinda don't fully understand SERCOMS and other such internals, so what's missing?

I printed the adafruit library pdm object internals and they are this but don't really help me...

_gclk: 3
_clk: 10
_data: 7
_clk_pin: 10
_clk_mux: 6
_data_pin: 7
_data_mux: 6
_i2sserializer: 0
_i2sclock: 0

No point posting any code, it's just pdm_analogout example code with pins changed.

2

Can you post a schematic of your board? Did you prototype this before building a PCB, if so what were the results?

3

This is still the prototype pcb, definitely found a few mistakes (as always lol) but I soldered around them and the arduino part works. I had to change the port mapping in FastLED library, figure this issue is related with the PDM library too, there's a lot of #if defined(ARDUINO_SAMD_ZERO) stuff in there...

Here are the relevant parts of the schematic and layout: Imgur: The magic of the Internet

Oh and this is the mic

4

That looks like part of the PCB layout not a schematic.

5

It's an imgur album that has 3 pics, two of which are the schematic, not sure what your os is, all 3 show up in a vertical list in my windows chrome...

6

I am using chrome on linux and I see three vertically. The middle one has a ton of data on it like maybe part of the gerber or cad file. I have no clue as to how this is powered The third appears to be a connector. Your link shows both analog and digital outputs from the microphones. You need to narrow it down. It shows your mice is connected to the NMI.

7

Fixed, the problem was that the ZeroPDM library's configure() assumed certain MUXes from EPioType for certain pins based on a mapping from somewhere in the real SAMD Core, which didn't hold true for my variant's modified samd-core. So it picked MUX_PA10G_I2S_SCK0 -> 6 -> PIO_COM to pass into pinPeripheral() but 6 is actually PIO_ANALOG_DAC in Mattairtech's WVariant.h. I used PIO_COM(15) directly for both data and clock pins and voila.

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