Special projects deserve special components, which is why a display with unusual dimensions acts as the basis for my living room music system. However, the path to the final version was fraught with challenges.

A web radio based on a Pi Zero (Figure 1) came to life in 2018 as a lightweight tinkering project with a keyboard, mini-speakers, and a small LCD screen [1]. Now, however, it has found a permanent place on my audio/visual (AV) receiver (Figure 2). Today, it is no longer controlled by a keypad, but by an infrared remote control. This solution works well, but it has one obvious drawback: The display is simply too small for couch potatoes.

Figure 1: The original version of the web radio started in 2018 as a small tinkering project.

Figure 2: One drawback of the original project was a too-small LCD.

Therefore, a new version of the project has been in the pipeline for quite some time but has failed to materialize thus far because of the available display alternatives. In contrast to the current solution, which simply wires the display, the IR receiver, and the Pi Zero with a few jumpers, I wanted the next version to match the existing device landscape in terms of appearance. However, large displays have had a fairly off-putting format until now, and so the project didn't really get off the ground.

Rare Beast from Waveshare

This situation changed all of a sudden when Waveshare launched a touch-enabled TFT display with a 1280x400-pixel (px) resolution (Figure 3). Waveshare is well known in the small-board computer (SBC) scene, because the company provides displays in many different sizes, not just for the Raspberry Pi, and it has good support in the form of a wiki and various GitHub repositories. The price of the display is a bit steep at EUR110 (~$126), but it promises to be an eye-catcher.

Figure 3: The Waveshare display with its unusual form factor.

The package includes the display with an aspect of 19.1x6cm (7.5x2.3in), some spacer bolts, a normal HDMI and USB cable, and various special adapters (Figure 4). The display's bezel is 8.35mm (3.3in) wide on the left and right, but only 4.7mm (1.85in) at the top and bottom.

Figure 4: The display comes with some special adapters.

Thanks to the adapters, you can install an SBC directly behind the display; they support the Raspberry Pi 3 and 4 and the Jetson Nano. The installation is a bit tricky, because precisely built adapters are needed for everything to fit – and they are not. In the end, mounting the Raspberry Pi with screws or spacer bolts proved to be the best solution, leaving a bit more space for the HDMI and USB adapters.

The display draws its power from the computer over USB; alternatively, it can be connected directly through a micro-USB socket. The touchscreen also uses USB and does not require a driver installation. The screen outputs its sound with a 3.5mm jack. For this to work, the Raspberry Pi has to switch the sound to the HDMI 0 output.

The display's moderate power consumption is not a problem for the intended use. Even with the VLC media player running and visual effects enabled (Figure 3), the power requirement of a Raspberry Pi 4, including the display, is only 1,100-1,500mA. However, even the fourth generation of the Raspberry Pi has not yet learned how to turn off its peripherals after shutdown, which means the system still consumes 250mA when switched off. Although not much, it is annoying because it is so unnecessary. The system could not be marketed as is, because devices are only allowed to consume 0.5W in standby in most countries.

Gearing Up

The display works with a normal Raspberry Pi OS, but its unusual dimensions necessitate a number of settings, which the device wiki [2] describes quite well. The (slightly adjusted) configuration of the first HDMI interface from the settings in the /boot/config.txt file is:

[HDMI:0]
hdmi_group=2
hdmi_mode=87
hdmi_timings=400 0 100 10 140 1280 10 20 20 2 0 0 0 60 0 43000000 3
display_rotate=3

The default orientation of the display is vertical; the display_rotate parameter changes that – but only for the pixel output, not for the touch orientation, which has to be done by the X server (more about this later).

Because the Raspberry Pi 4 has two HDMI outputs, all special configurations for the 19.1cm display are below the [HDMI:0] filter. You can easily connect a normal display to the other HDMI port and set up the computer this way. The 400px height of the Waveshare screen is not enough for some dialogs; the OK and Cancel buttons often disappear irretrievably at the bottom of the screen.

Later, when used as a web radio, the second HDMI port is not connected to a screen at all, but to the AV receiver. More settings are then needed:

[HDMI:1]
hdmi_group=1
hdmi_drive=2
hdmi_force_hotplug=1
hdmi_ignore_edid=0xa5000080
hdmi_force_edid_audio=1
hdmi_ignore_cec_init=1
config_hdmi_boost=4

In particular, they ensure that the output is configured correctly for audio output, even if the receiver is not yet running.

You can correct the touch orientation from the /etc/X11/xorg.conf.d/40-libinput.conf configuration file. Add a new Section with the lines from Listing 1 (to match the rotation from /boot/config.txt). The X server's input framework then controls the orientation with CalibrationMatrix. The Waveshare wiki provides the correct values.

# Match on all types of devices but joysticks
#
[...]
Section "InputClass"
  Identifier "libinput touchscreen catchall"
  MatchIsTouchscreen "on"
  Option "CalibrationMatrix" "0 -1 1 1 0 0 0 0 1"
  MatchDevicePath "/dev/input/event*"
  Driver "libinput"
EndSection
[...]

The Raspberry Pi 4 offers three options for the sound output: analog output through the jack socket and two digital outputs via HDMI. The commands

$ pactl set-default-sink 1
$ pactl set-card-profile 0 off
$ pactl set-card-profile 2 off

give you the correct configuration for the PulseAudio version used by Pi OS as the default. You can also do this in the graphical user interface (command pavucontrol), but it is not so easy on the touchscreen. Annoyingly, many applications remember the output channel you use, so it is important to set up the configuration as early as possible.

With a working screen and sound output, the purely technical side of commissioning is now finished, but a nice screen with a mess of tangled cables is not something you would want in your living room.

In the Box

One of my goals for the project was, as I said earlier, to create a device suitable for the living room. And that means investing in a case; because I have access to a 3D printer, this is theoretically not a big problem. However, some pitfalls lurk compared with the basic setup of the operating system, as you can easily see from Figure 3, where the power connector and the HDMI cable for the sound output are jutting out vertically from the screen.

Preferably, all of the Pi's ports would be on the back of the case, but because USB and HDMI ports have to be installed "inside" the display, this is not possible by design. The problem has been around since the very first Raspberry Pi, independent of the Waveshare display. A Raspberry Pi in a larger case always makes for a tricky install, because the important ports (if you count the SD card) are distributed over three sides.

Fortunately, some simple solutions are available. For example, I have never had a microSD card die on me. Once installed, it just gets on with its job and does not need to be accessible from the outside. Moreover, the LAN is not needed for the web radio, but if you do need the connection, simply buy a network coupler for a little money. On the inside, you need a short patch cable to the coupler.

The power supply is easy to solve, because you can also power a Raspberry Pi over pins 2 and 4 (5V) and 6 (GND), bypassing the built-in protection mechanisms with acceptable risk. Depending on your preference, a micro-USB, USB-C or barrel jack is then connected to the back of the case, which you connect to the pins with cable on the inside.

When it came to USB, I decided to go for a mini-extension (plug to socket) on the back of the case. Because this presents four USB ports, two are free for other purposes (e.g., an internal hard drive). A socket at the front wouldn't be bad either, but the 3D printer I have access to doesn't give me the scope to do that; the screen itself is 19cm wide, and with 3cm of margin on each side, this fully utilizes the printer's available width. In Figure 5, you can see the chassis base plate with the connectors.

Figure 5: The case with the cabling for (left to right) USB, HDMI, and power.

The second HDMI port ultimately turned out to be the biggest challenge. It is only possible to route the cable out neatly to the back with a suitably angled plug. Because I have a Bluetooth-enabled receiver, I don't actually require the connection to send tracks, but the Raspberry Pi has never had a reputation for a stable, automatic Bluetooth connection, which is why this solution is a backup at best.

Finally, I found what I was looking for on BerryBase [3]: HDMI cables that you can assemble yourself, including sockets and plugs and even angled versions (Figure 6). A regular socket was attached to the other side of the ribbon cable, but it does not have mounting holes. Precise 3D printing dimensions without play then ensure that the jack is held to the back of the case. The construction does look a bit untidy, because the ribbon cable is not shielded at all. My Denon receiver, which is otherwise extremely sensitive and refuses to cooperate with various cables, fortunately had no problem with that.

Figure 6: HDMI flat ribbon cable by BerryBase.