A Custom Screen Add-on for the Raspberry Pi 400

The Pi 400

When it was released in early November, the Raspberry Pi 400 was heralded as an innovative device. With the full power of the Raspberry Pi 4 crammed into a keyboard chassis, setups could now be much cleaner.

But there was still a drawback: adding a display still required using a mess of cables that clutter desks. This problem is what inspired Reddit user u/jwktje to do something about it.

Display Choice

There is a pair of micro-HDMI ports on the back of the Pi 400 for transmitting video signals to a display. However, because the aim of this project was to minimize cable sprawl, an external monitor that uses an HDMI cable and either USB or an external adapter for power was out of the question. The solution was the Pimoroni HyperPixel touchscreen, which is able to be driven by the Pi's onboard GPIO pins.

Although it uses all of them (yes, ALL), it's a better alternative for users who don't require access to the GPIO pins. There is an added benefit as well in that the screen has touch capabilities, so a mouse isn't required either, thus saving an additional cable.

Design and Fabrication

The screen is fitted inside of an enclosure that keeps it securely held in place with a clip underneath and a riser. The 40-pin female header on the display slots into the exposed male pin header on the back, which requires the whole system to be mounted on the right side of the Pi 400.

u/jwktje 3D-printed the enclosure with white, translucent filament- probably to see the onboard indicators better.

Transmitting an Image

After physically installing the screen, a script from Pimoroni was run that first builds a custom overlay object downloaded from the Github repository and moves it to the overlays directory within /boot/overlay/. This causes the Pi to send display signals to the LCD. Touchscreen information is communicated via I2C, which lets the Pi know the X/Y coordinates of where a person is touching.