pHAT DAC on model B


#1

I’ve been given a pHAT DAC which is intended for model B+ (or Zero) but which I want to use on my old model B (which has lousy sound). But the pHAT-DAC has 40 pins and the model B only 26.

Looking at the pinout it seems that the pins that are needed are probably in the first 26 and so compatible with the model B. If I cut down the header to 26 pins will it be likely to work?

Any advice gratefully received!
Thanks
Richard


#2

If you don’t want to hack anything irreparably you could try using a 26-pin stacking header on the Pi to extend the pins above the obstacles and just plug the 40-pin pHAT on top.
Couldn’t find anything in Pimoroni’s listings but the Pi-Hut have an adafruit header you could use.


#3

The i2s pins on the older Pi were available via the P5 header- you would have to be pretty creative to wire the pHAT DAC to them.


#4

Thanks Gadgetoid - but P5 seems to be only on the B+, I have a model B. Do you know if/where I2S is available on the model B?

I’m struggling to find a proper description of teh 26 pin connector signals, equivalent to this for teh pHAT-DAC and B+ etc.

I’d hoped to do something similar to neilman’s suggestion.

PS: Thanks neilman. That header is exactly what I need.
Cheers
Richard


#5

There is another adapter you might possibly consider from AB Electronics - they make a Pi3-40 pin to Pi2-26 pin adapter board. Actually intended to allow old 26-pin HATs to be used on the newer 40-pin Pi’s. It is a passive board (no converter chips). By swapping the header genders it might be possible to provide reverse conversion if you can live with the mechanical arrangement. You’ll still have missing pin function beyond pin 26 but that can’t be helped.


#6

Hmm, I was mistaken in my assertion that “the pins that are needed are probably in the first 26” - the pHAT DAC needs I2S pins BCM19 and BCM21 which are on 35 and 40 of the later connector, and absent from the P1 on my old model 1B. Which is why my pHAT DAC doesn’t work!

So the question is - please can anyone advise where (if?) these can be found anywhere on an early model 1B. I don’t have a P5 connector!

Are the schematics publicly available?

Thanks
Richard


#7

On the very first release of the Pi B, you’re out of luck I believe (I haven’t even seen one for many, many years now!) but the slightly revised version - not the B+ but a revised B - should have a P5 header as detailed here: https://www.raspberrypi-spy.co.uk/2012/09/raspberry-pi-p5-header/

I believe the required i2s pins are available on here, but I’m not sure.


#8

Yes this is an early model B, without P5.

I’ll try asking on the raspberrypi.org forum. Maybe someone there will know if BCM19 and BCM21 can be accessed on this hardware.

Thanks again
Richard


#9

Answering my own question in case anyone else wanting I2S with an early model 1B stumbles on this thread:

This post on the Raspberry Pi forum discusses I2S connections on the Rev 1 Model B.

I will post again if/when I have sussed what I actually need to do…

Richard