Official poe hat with hyperpixel 4.0

Hi all,

Is it possible to power the hyperpixel 4.0 with the official poe hat? And if so, are there any best practices for such a combination?


According to its specs the POE hat can deliver the same 2.5A the official power supply can so I would think its doable. Your going to need a stacking header with long male pins.
The 11mm one here may work, I’m assuming the pins can go right through the POE hat GPIO header and extend up the top side.

I can’t find its GPIO pinout but I don’t think it uses anything other than the ground and +5V pins.
You’ll just have to watch the clearance to the POE hat cooling fan. Finding stand offs might be tricky depending on what the final spacing ends up being. I think your going to want at least 4 of the standoffs with the threaded studs on one end. Like in this kit.

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Thanks a billion.

The Poe hat uses i2c for fan control. Would that render a problem? (I’m not that familiar with that protocol.)

Yes, it could be a problem. Devices can share that bus as long as no two have the same address. So it wouldn’t normally be an issue. Problem is the Hyperpixel uses all the GPIO pins and reassigns the normal i2c pins to a different function. There is an i2c header on its back side but I can’t see how you could easily use it with the POE hat plugged into the GPIO.
And I’m not sure what will happen even if you don’t use the fan speed software? I would imagine the POE Hat will be auto ID’s by its eprom and all the software setup automatically? Might have to ask about that on the Pi Foundation Forum. You may be able to disable it from using i2c and just leave the fan running at full speed, or not running at all?

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The Official Pi post says that an additional hat on the POE is possible.

It also links back to the Pirates for which headers to buy (same as the ones @alphanumeric pointed you too).



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The hyperpixel is a bit of an exception though. Its not like a traditional HAT. i2c doesn’t work the normal standard way it does on any other HAT. Those GPIO pins are used for something else. That complicates things in this instance.

Hi there,

Chiming back in on this one - did anyone get a definitive outcome on what happens when you put a Hyperpixel 4 atop a foundation POE board ? Obviously the HSync and VSync functions are on the normal i2c bus pins - but do they co-exist okay or bomb out ?

I don’t have either device so I can’t test it. I would think the Hyperpixel installer turns off i2c and repurposes those pins for its use. The POE hat may still work, you just won’t have any fan control.

The hyperpixel does indeed repurpose the i2c pins as DPI H and V sync ( but it then does break out the i2c pins to a molex header, suggesting that other i2c devices should be allowed. I have successfully read breakout garden modules from the molex i2c connector but I’m not sure from of the route it takes.

I was going to mention the i2c breakout on the back of the hyperpixel, but that wouldn’t be very easy to use with the POE hat. I think thats done with software and or hardware on the hyperpixel. Its a secondary software i2c, something like that? The product page says " alternate I2C interface ".
The Bilge Tank video may say how they did it, if you hunt it up.

EDIT: This is what it says on the pinout page, “Because HyperPixel 4 uses every Raspberry Pi pin it’s difficult to use it in conjunction with other devices, but it does break out the software I2C bus (i2c 3) which you can share with the touchscreen controller.”

The question was whether anyone had physically tested the result - I’m familiar with the characteristics of both the POE and the HyperPixel 4, just not their behaviour together.

I’ve got 3 POE HAT’s arriving tomorrow - I will give definitive findings once I have tried these together.

I might have a look shortly to see how much fanshim breaks HyperPixel 4 …

The fan shim uses a couple of GPIO pin’s and I think i2c for the LED.

Yes - I know , and of particular frustration uses the same PWM as most i2S sound cards introducing lots of crackle on BB5122 and no audio via SPDIF on WM8804.

This is about real findings rather than rumour or theory which sadly doesn’t go anywhere in resolving issues or queries.

You may be the first one to try it?
The POE hat wasn’t designed “as far as I can tell anyway” with the intention of stacking another Hat on top of it. Thats likely dissuaded people from trying to do it.
And the Fan Shim was only just released. More info on how it works would be good though. At least a pinout. My guess is the Pi 4 early release has caused some delays with other stuff.

Re fanshim and hyperpixel4: they are usable together, you just end up with a pinkish tinge to the screen!