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Raspberry Pi CM4 Сarrier with Hi-Res MIPI Display

An interface breakout board for Raspberry Pi Compute Module 4, permanently attached to a 7" IPS touchscreen display

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Back in 2019 we developed a carrier board with Raspberry Pi CM3+ and a high-resolution touchscreen. We have been anxiously waiting for the CM4 ever since Raspberry Pi 4 became available. It's finally here! Now we're ready to develop a CM4-based module and make it available as an open-source project.

The board will have:

  • standard RPi 40-pin header for peripherals and integration
  • connector with 4-lane MIPI DSI interface for display
  • connector with I2C interface for the touchscreen
  • micro-SD card holder
  • USB 2.0 host connector
  • PCM audio amplifier with 3W speaker output
  • USB-C power connector
  • micro-USB connector for flashing the on-board eMMC
  • general purpose push button
  • power and activity LEDs
  • mounting standoffs

All components are surface-mounted on one side, making the resulting assembly slim and good for wall-mount applications like a smart home dashboard.

There is a challenge to overcome: we need to hack our way through the undocumented MIPI 
DSI peripheral to make the interface work. With the CM3+ module, we used an HDMI-DSI bridge, which is an expensive and hard to source component. This time we want to do things differently and connect the interface directly to the Raspberry Pi Compute Module. Broadcom and Raspberry Pi Foundation are hesitant to release the documentation for the peripheral and reserve this interface for official displays. However, the source code for the driver is available, giving us a good starting point. We may need to adapt it to our display and switch the interface from 2-lane to 4-lane mode to support the higher resolution.

Let's start hacking.

PYXIS-CM4-BD-1.png

Block Diagram

Portable Network Graphics (PNG) - 82.31 kB - 01/05/2021 at 18:27

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  • 1 × Display
  • 1 × Raspberry Pi Compute Module 4
  • 1 × Custom board

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Richard wrote 01/30/2022 at 23:26 point

I was wondering how difficult it would be to create a board that could drive a laptop screen to do away with the HDMI LCD driver board. 

It would be something like the ebay listings advertised as "HDMI VGA 2AV Reversing LCD Driver Board for 13.3" LP133WH2 1366x768 LCD panel" but cutting out the HDMI cable, separate driver board, multiple power supplies etc

I have been looking at options for connecting a pi running magic mirror (or similar) to an LCD to put behind a mirror but making it as thin as possible.

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Dan Pastusek wrote 01/22/2022 at 21:15 point

Very cool project! Is there any way to buy one of these populated production boards?

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StonedEdge wrote 06/19/2021 at 10:02 point

This is excellent! I’m currently building a gaming handheld in the form of a Switch Lite and we would have absolutely have loved to use a 5.5” MIPI display with capacitive touch screen, but there is just no driver information available on anything right now, so we had to settle for HDMI and a 5” 800 x 480 panel (yuck). 

I did think about using a MIPI HDMI bridge chip, but I hope some day direct driving the panels will become more accessible for us hobbyists. Awesome work, keep it up and I hope you could work on a 5.5” driven via MIPI someday too. I’d integrate it immediately lol

Here’s our project :) 

Cheers,

Ben

https://www.raspberrypi.org/forums/viewtopic.php?f=98&t=289529&start=7

https://bitbuilt.net/forums/index.php?threads/retro-lite-cm4-a-stonededge-and-dmcke5-collaboration.3934/

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Brett Smith wrote 06/11/2021 at 19:58 point

Are any of the schematics, PCB files, or code available???

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Igor Shturma wrote 06/17/2021 at 06:02 point

Hi Brett, I got very busy the last month and had to put this project on hold. There is some issue that I need to find and fix in the last revision. Once I do this, I will share the files here. Hopefully, in a week or two.

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Brett Smith wrote 06/18/2021 at 03:40 point

Thank you, great work!

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Giovanni wrote 02/17/2021 at 05:57 point

Awesome, I've always wanted to use DSI on my RPi 3B+. It'd be interesting if there were an e-ink/Reflective LCD in that format- some Reflective DSI screens use 20pins, whereas the Rpi use 15. Nonetheless, It would be interesting to see more of those.

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ddB0515 wrote 01/28/2021 at 23:39 point

Such a nice progress, I have played for a while with touch digitizer for Nexus 2nd gen and made whole touch controller board for it based on Ilitek 2511, more details you can find here: https://budimir.cc/2020/04/21/asus-me571k-aka-nexus-7-2nd-gen-touch-digitizer-reverse-engineering/

Need to finish all optimisation for touch screen but I got it working :)

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nick4yy wrote 01/28/2021 at 11:27 point

great project, congratulations !!
is it possible to buy such an expansion board for CM4 ?

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Manny wrote 01/07/2021 at 06:45 point

Seems like a great initiative. Looking forward to your updates as you progress toward a first release. 

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