PIC24EP - PDM sampling / library to PCM

benoitstjean · Posted: Mon Mar 18, 2024 8:04 pm

Hello again,

Anyone has a PIC library to sample and convert a PDM bitstream from a MEMS microphone to PCM (16-bit 16kHz or something equal or greater than to 8bit 8kHz)?

Thanks,

Ben

Ttelmah · Joined: 11 Mar 2010 Posts: 19495

You are going to need a serious PIC. A lot of mahs involved, you have to
generate a LPF,, then use a decimate function. You need something with
a serious amount of RAM and processng speed. So a DsPIC probably.

benoitstjean · Posted: Tue Mar 19, 2024 12:38 pm

Hmmm.... Even if I'm running internally at 129.042MHz?

I found an ADI IC that does it but it's so small and it's a BGA, there's zero way for me to do solder it manually. I do 0402 by hand and some smaller stuff through a microscope but that ADI IC is way way way smaller at 1.3mm x 1.4mm, 9 pins, BGA.

I use a lot of the TLV320AIC3204 CODECs and in one of the manuals, there appears to be a PDM input for digital mics but there's no further explanation. I wrote to TI support and they're usually pretty good so I'll wait to see what they have to say.

Thanks!

Ben

temtronic · Posted: Tue Mar 19, 2024 2:44 pm

Hay Ben
Does ADI have a 'demo' PCB available ?
While it might be pricey, it'd be a god way to R&D to even see IF what you want to do is possible.

So last day of fall and I have SNOW here in hamilton.
arrgh, tonight Spring comes and the white better be GONE tomorrow !

benoitstjean · Posted: Wed Mar 20, 2024 10:27 am

Yeah ADI has a kit, price is not the issue, soldering is the issue. The IC is so small AND it's BGA. Can't do it by hand. Anyhow, I currently use the TLV320AIC3204 and TI gave me pointers as to where to look on how to use it. It's a bit basic for information but I'll have a look.

Thanks.

benoitstjean · Posted: Wed Mar 20, 2024 11:00 am

The kit is only 179.67$ CAD at DigiKey:

https://www.digikey.ca/en/products/detail/analog-devices-inc/EVAL-ADAU7002Z/3991573

Again, this is all nice and fine but the friggin' IC is 1.56mm x 0.76mm 8-ball wafer-lever chip. Not sure if there's an easy trick to solder this by hand...

Anyhow, will get the dev kit, hook-it up to my PIC24 and see how it works-out for PCM.

temtronic · Posted: Wed Mar 20, 2024 11:03 am

In the 'dinosaur days', I tool a demo kit PCB and turned it into a 'daughter' board for a few projects.
Course back then stuff was a LOT bigger...and I could READ the part numbers of DIP Chips....
sigh....