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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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initrd 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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