We have a place to mount a power button here:
We added it for development purposes so you could use that, here’s a close up of the pins:
The part number for this switch is KMR731NG - you should be able to get one easily and soldering won’t be that difficult 
Thank you very much! I’m excited to get going on this again. This is above the call of duty. If I can make your management aware, I’d be glad to.
No worries, glad to help!
New user here - I’ve been considering all of the options for converting to pi4, and they all have their benefits and drawbacks.
The method that @JeffS451 used is just the business, and I nearly went that way, but having soldered more than a few HDMI cables recently, I got cold feet. HDMI is super sensitive to interference between the wires, so even a mistake free solder job could end up giving a “noisy” image, or just not working.
@Steve has a setup that I like, and I may just go with that - already have the necessary FPV cable parts, and a longer 20pin FPC cable coming for the battery/keyboard connection to the hub.
But I had an idea, and I was wondering if it was absurd or no. with the full cooling bridge in place, the hub 2.0 has to sit pretty far away from the pi. I also don’t really care about preserving the GPIO pins into the modular rail - I only need SDA and SCL to allow interaction with the hub, and power/ground/board detect. I looked for the right BTB 0.8mm 2x20 4mm mated vertical post socket to whip up a custom bridge with just those connections, but that proved fruitless. The closest I could find that looked correct was $20 for a single piece.
Then I thought, why not hack up the stock bridge? Just keep a section big enough to cover the hub, and solder to the appropriate traces, which I found with a magnifying glass, razor to expose some traces, and a multimeter. Seems like it could work just soldering the cut end of a Dupont wire to those traces/ground for the five necessary wires, and simply plugging the dupont ends in on the pi4.
But then I had to deal with the power circuit on the bridge. That straddles a 5v path to the pi GPIO pins on one side, and the 5v path from the hub on the other. I’m thinking I could dremel that section out whole, and glue it to the top of the amputated hub end of the bridge, then jump a ground wire and each 5v path up to it. With the 2x20 female gpio section of the bridge removed, that would mean the hub could go right up close fo the pi - even straying on the sliding portion of the rail.
So far as I can gather, it should work - but maybe I’m missing something about that power circuit.
*note the red wire in the pics is connected to a toggle switch that brings board detect to ground. Wanted to see the pi-top boot without a pi connected - which it did, though I was unable to get a video signal to display on the screen with two different sources? For one it played a sort of screensaver type effect for a couple of seconds, but never did display an image, though the video sources (iphone with hdmi out, and macbook, both set to 1080p) saw the display as connected.
Hello! I really like watching the various efforts being made to up the power of thepi-top [3]. Personally I suspect that if they just released the part that plugs into the the side of the Raspberry Pi 4, the folks who play here would figure the rest out 
and there would be less cutting of cables apart!
Latest with my mod. A while ago broke the cable going to the screen, so I have found another use for the chassis. Removed the screen and now this is a PiTop 400 Unit (with a mouse), just need to port the HDMI to the chassis and it’s all good to go!
In case you want to use a RPi CM4, rather than RPi4B+, without having to physically modify your pi-top [3], you could use this:
https://www.waveshare.com/product/cm4-to-pi3-adapter.htm?___SID=U
Using the board stated above in my build, running Raspbian 5.15.61 kernel atm.
full details are here Pi-top[3] with CM4toPi3 board
Be sure to run below commands in case of using Raspberry Bullseye. This will give you the battery icon and working ‘special keys’ (i.e. Brighthness control)
> echo "deb http://apt.pi-top.com/pi-top-os sirius main contrib non-free" | sudo tee /etc/apt/sources.list.d/pi-top.list &> /dev/null
> curl https://apt.pi-top.com/pt-apt.asc | sudo apt-key add
> sudo apt update
> sudo apt install --no-install-recommends -y pt-device-managerCan’t figure out why my PI4 won’t boot up. Have the HDMI and ribbon cables extended but power LED only flashes green three times and goes back to red. PI4 works fine on it’s own. Any suggestions?
Check the connection of the bridge board, it can be miss-plugged
double/triple checked all of the cables on the board. Removed and reinstalled the ribbon cables - all looks good. The hub seems to be secured as possible to the board as well. Tested with a Pi Zero just for the hell of it with same results. Don’t have a Pi 3, so unable to see if it’s a problem specific to the hub or board.
It’s hard to tell from the pictures, but to me it looks like the bridge is offset to the right. Check if you can insert the screw.
Also your flat wire cable looks odd. The white side is typ. used as Pin1 indicator; you have it the other way around. have you measured your GPIO40 before you’ve connected the bridge? Is Pin1/2 in the correct position?
I’ve mad a similar test but used a different cable like https://shop.pimoroni.com/products/40-pin-gpio-extension-cable?variant=32246715580499 -> please mind their note in the product description!
Looks like it was the cable. Also got a thin ribbon USB cable. Working like a charm. Thanks for the help!
I seem to have scored a couple of CM4 boards, so I bought a couple of the CM4 to Pi 3B adapters. Has anyone tried to build a Pi-Top with one of these setups yet? I’m pretty sure it will fit (maybe a little bit high, but within coping distance). Heat: It looks like the CM4 SOC metal chip lid will be hard against the green plastic bottom of the laptop. I don’t have any great ideas for this. I could cut a window in the bottom, but I don’t think that would be very effective. I’m not going to use this as a compute cluster, but… Hmm. How about a thin aluminum heat spreader like the Pi-400? It would have to thin, but maybe that would be a reasonable solution and keep the bottom of the laptop intact. I also have one of the aluminum Astro-Pi cases, that take Pi 3’s, so I am hoping the Waveshare adapters are good.
rpiMike posted about this in the above thread.
Don’t do this. Don’t spend your money until we come up with some better way.
Given the Waveshare CM3 to Pi 3B adapter, which mounts the CM4 on the bottom, it just plain does not fit. @Tom-B, above had to cut a whole in the bottom of the laptop the full size of the CM4. From my efforts to just squeeze it in somehow, I think he’s exactly correct about this. There are several problems, but the big one is heat. It can’t use any heatsinking from the metal bridge, and just cutting a hole in the bottom isn’t going to allow convection.
I was hoping to get it to just fit and then buy some aluminum sheet material to make a heat spreader across as much of the case bottom as I could. That’s how the pi-400 does it.
Can’t second this!
Also made such a mod, covering the resulting hole with a piece of GFK.
The PI is just working fine. Keep in mind that a CM4 is designed to work without cooling.
Adding a alu plate (with some TIM material to the SOC) will result in the alu getting hot to the touch! One can burn its finger touching it.
Having the CM4 on top of the carrier would be beneficial, but there is no such carrier around.
For more powerful boards than the libre alta, the easiest solution seems to be this: https://www.waveshare.com/zero-to-pi3-adapter-a.htm
Pi zero to 3b adapter, this maintains all rear ports.
Then use a 40 pin GPIO extender, 2x USB C female to USB A male extenders, Micro HDMI female to HDMI male extender and audio extension cable.
This should make it possible to place the new board in the right hand side of the case.
