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Pins 82 and 84
See pin assignments on page 10.
Oh, sorry for not being clear

What I mean is that my adapter board is not even connecting the CM4's GPIO44 and GPIO45 to the equivalent CM3's pins 82 and 84 (or to any other pins)

My only solution with this board seems to be to connect the I2C devices to GPIO0 and GPIO1 (the other I2C bus) and change the software to grab the joystick changes from there. That's why I was asking if the Freeplay board was maybe exposing them so I could "simply" solder the L2R2 Dual Analog (4 ADC) Add-On Board to them instead of GPIO44 and GPIO45
It will probably take me a while to get that information for you. It might not be until Monday or Tuesday. Do you know if there’s anything else on your adapter board that would be something that you can solder to? Then you could run wires over to 44&45 on the FPCM3.
That's ok! I can work on modifying the case

I took a deeper look at the board and it doesnt have anything connected to those pins and to be honest I don't think I can pull off soldering magnet wires to those small Hirose connectors
Here's an update on the case:

I had to trim a lot on the back to let the CM4 come out of the case. This board's dimensions allow for a little bit of the top screw posts to still hold the screws even if almost half of them needs to be shaved off. I broke one of them when using the dremel tool but nothing too bad that a little bit epoxy can't fix Big Grin

The board has a reset button on the left side, which can be accessible and still have enough room for the screw to keep the whole thing together.

A little bit of the cartridge slot had to be shaven off too, to give the board more room to come out of the case
See the attached screenshot from the CM4 datasheet.  


First, note that it DOES have a GPIO 44&45.  It's odd to me that the makers of the adapter board didn't route those to pins 82&84.  That's an oversight, in my opinion.  They really should have routed those 2 pins.

Next, note that the CM4 has several other i2c busses.

UNFORTUNATELY, our Freeplay CM3 does not route GPIO0, GPIO1, GPIO2, or GPIO3 (which all would be top choice alternatives for i2c-0 or i2c-1).

So, now, you have to find another pair and repurpose it, I guess, and things could get complex.

Here's a screenshot of the Freeplay CM3 connector.  Note that, even though things like GPIO0 and GPIO1 are labeled, that's from the CM3 perspective, not the Freeplay perspective.  


MAYBE you could find a spot on the adapter board where GPIO0&1 _or_ GPIO2&3 were somehow easy to tack wires to.  Those can be set to i2c.

If they actually route pins 80/82 from the CM4, it would be good to find where they go.  This would be the best option (GPIO44/45).
My board's manufacturer for some reason claims the CM4 only has 28 GPIOs. So GPIO28 and above are simply not connected to the board. If I had to guess, I'd say this board was designed to accomplish a different goal and now it's sold as an adapter board. But who knows.

There's nothing on the board to solder to, but I can probably solder directly to the pins (or scratch off the traces) and solder a connector to easily connect and disconnect it to the Freeplay board.

I'll update here as soon as I can.
I think you have this one, right?

They are almost correct in saying that it only has 28 GPIOs.  Notice on the screenshot of the CM4 datasheet (I posted in my previous message) that it shows GPIO0-27 on one page and then GPIO44-45 on the next page.  I think that 44 and 45 are the only ones over 27 that the CM4 has.

The board we used (which has different problems) looks like this.
(also see

Notice that they route "I2C_SCL" and "I2C_SDA" from the CM4 pins 80 and 82 to CM3 pins 82 and 84.  These are the GPIO 44 and 45 which the Freeplay CM3 uses.

I think it's an oversight/mistake that Geekworm did not route these.

If you're going to try to solder to something small, you could maybe first try to solder to pins 3 and 5 on the Freeplay CM3 and run them to the "44" and "45" solder holes that the add-on board uses.  That could be tricky, but it'd be the best case, in my opinion.

My pen is pointing at pin 1 here, so 3 would be next to that, and 5 would be the 3rd pin in.
Here's also another interesting option.

It seems like they do another sort of odd thing and route GPIO44/45 from the CM4 to where the CM3 would have GPIO28/29.  That's not great, except that the Freeplay CM3 routes those to R29 and R30 and then to GROUND.  This just gives a better spot to try to solder to (after removing the R29/R30). 


It's a thought.  I'm not sure if it's better than the route you're already going.

FYI, they also have this interesting Zero->CM3 adapter, too.
Oh, and you might want to see if there's a chance that the Geekworm board actually does the same thing as the Waveshare board.
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