Page 1 of 1

CM3 Breakout Board Resdesign

Posted: Tue Mar 22, 2016 6:07 pm
by nsbrown93
Hi Everyone!

We are a small startup company looking to design our own breakout board for the existing compute module. We would love to use the new CM3, but we need our electronics done now and nobody is sure when the new model will be released.

My question is: will it take a significant redesign of the custom CM1 breakout board if we upgrade to the CM3 in the future? The current plan is just to make a simpler version of the dev board with only the camera interfaces and a few GPIOs. I'm anticipating the only redesign we would have to do is flip wires to different pins if the CM3 pinout is different, which should be fairly quick and simple.

Any second opinions/educated guesses on this? I realize not many details on the CM3 have been released so it can't be answered for sure.

Thanks!

Re: CM3 Breakout Board Resdesign

Posted: Tue Mar 22, 2016 7:39 pm
by fruitoftheloom
nsbrown93 wrote:Hi Everyone!

We are a small startup company looking to design our own breakout board for the existing compute module. We would love to use the new CM3, but we need our electronics done now and nobody is sure when the new model will be released.

My question is: will it take a significant redesign of the custom CM1 breakout board if we upgrade to the CM3 in the future? The current plan is just to make a simpler version of the dev board with only the camera interfaces and a few GPIOs. I'm anticipating the only redesign we would have to do is flip wires to different pins if the CM3 pinout is different, which should be fairly quick and simple.

Any second opinions/educated guesses on this? I realize not many details on the CM3 have been released so it can't be answered for sure.

Thanks!
There is a hyperbole CM3 thread here: viewtopic.php?f=98&t=141248

Re: CM3 Breakout Board Resdesign

Posted: Tue Mar 22, 2016 8:43 pm
by W. H. Heydt
It has been mentioned that one of the RPF people that has been working on the CM3 is also part of the group that developed the Slice TV box that uses the CM. Therefore, he has a vested interest in seeing that the CM3 can be a "drop in replacement" for the CM. In addition, one of the RPF engineers has posted that he has a CM3 to test. If I remember correctly, he mentioned using it in a pre-existing development carrier board (the sort sort in the dev kit with a CM).

On the whole, I think it is virtually a given that a CM3 will work in any board that uses a CM now. My one hope--and no one has said anything about it either way--is that the CM3 has enough eMMC to handle a full Jessie install (that is, at least 6GB and more likely 8GB).

Re: CM3 Breakout Board Resdesign

Posted: Thu Mar 24, 2016 3:29 pm
by plugwash
I would suggest beefing up the "VBAT" power supply as I would expect the CM3 to be quite a bit more power hungry than the CM1 and would expect most of that extra power consumption to be coming from the "VBAT" line. I don't have exact figures for the CM3 but from what i've seen of pi3 power consumption I would think that 5W is probablly enough and 10W is overkill.

Other than that I think you should be good to go.

Re: CM3 Breakout Board Resdesign

Posted: Thu Mar 24, 2016 5:01 pm
by gregeric
The RPi3B uses the same 2306 buck reg as the original CM IO board, good for 1A on each of the 1V8 & 3V3 rails, so if you base your design on that, or something equally capable, it should be OK.

Re: CM3 Breakout Board Resdesign

Posted: Thu Mar 24, 2016 5:08 pm
by plugwash
It's not about the 1.8 and 3.3 rails, it's about the core supply.

Re: CM3 Breakout Board Resdesign

Posted: Thu Mar 24, 2016 5:40 pm
by gregeric
... which come from the 3V3 & 1V8 buck reg (3V3 to CM_3V3 & CM_VBAT, 1V8 to CM_1V8). Am I missing something?

Re: CM3 Breakout Board Resdesign

Posted: Mon Mar 28, 2016 4:57 pm
by gregeric
Ah figured out what I was missing: the CMIO board is unique in connecting Vbat to the 3V3 supply - other 2835 based Pi use 5V, while 2836/7 don't have the on-chip reg & instead have external core voltage regulator also running from 5V, allowing greater power for the cores than the 3V3 regulator could ever supply.

That 3V3 1A max on the CMIO won't be adequate, so yes, a beefier VBAT than that reference design should be allowed for.

A possible mod for the existing CMIO board to supply sufficient current for a CM3: remove R1 & run a bodge wire from CM_VBAT to 5V.

Re: CM3 Breakout Board Resdesign

Posted: Tue Mar 29, 2016 6:09 am
by dengamle
Use same pinconfig as Raspberry for the first 40 pins on your card. In that case more people can use your card if all IO boards fit on top. 1wire and things like that.