Spotify Display

A 64×64 LED matrix that shows your current Spotify album art, and falls back to a daily weather forecast (with a clock) when nothing is playing.

Hardware

Raspberry Pi Zero W (single-core ARMv6) driving a 64×64 RGB LED matrix via rpi-rgb-led-matrix. Anything faster works too. A 32×32 panel is not recommended — album art becomes unreadable.

Recommended OS: Raspberry Pi OS Lite, 32-bit (ARMv6). The desktop image runs background services that compete with the matrix's realtime render thread for the single core.

Install

Dependencies:

sudo apt install build-essential libcurl4-openssl-dev nlohmann-json3-dev

Clone and build the matrix lib, pinned to a commit before the upstream Pi 5 RP1 backend was added (which ships inline ARMv7 atomics that the Pi Zero's ARMv6 assembler refuses):

git clone https://github.com/hzeller/rpi-rgb-led-matrix.git ~/rpi-rgb-led-matrix
git -C ~/rpi-rgb-led-matrix checkout e947417
make -C ~/rpi-rgb-led-matrix/lib

Then clone this repo, install the systemd unit, and write the device env file:

git clone https://github.com/mrrosoff/Spotify-Display.git ~/Spotify-Display
cd ~/Spotify-Display
sudo install -m 0644 startup/spotifydisplay.service /etc/systemd/system/
sudo install -m 0600 startup/spotifydisplay.env.example /etc/spotifydisplay.env
sudo systemctl daemon-reload

Edit /etc/spotifydisplay.env and set SPOTIFY_DEVICE_TOKEN to this device's secret (the value stored at SSM /website/spotify/device-secret). The Pi never holds Spotify credentials — it fetches short-lived access tokens from the token broker on maxrosoff.com. To (re)authorize the broker with a Spotify account, run sudo spotify in the website terminal. Then:

make
sudo systemctl enable --now spotifydisplay
sudo journalctl -u spotifydisplay -f

The Makefile downloads stb_image.h on first build (single-header JPEG/PNG decoder for album art). Override RGB_LIB_DISTRIBUTION if the matrix lib lives somewhere other than ~/rpi-rgb-led-matrix.

Behavior

• Polls Spotify every 5 s; shows album art while a track plays, with a paused-state overlay (50% dim + bottom-right pause icon) when applicable and a column-wipe transition when the track changes.
• After 30 s with no playback, switches to the weather screen, which shows the date, a clock in the top-right, the day's high/low/precipitation, and the condition word.
• Weather refreshes every 30 min from open-meteo (San Diego coordinates).
• Between 10:30 PM and midnight, shows tomorrow's forecast; from midnight to 7 AM, shows the current day.
• Dims the panel from 100 → 40 between 10:30 PM and 7 AM.

Notes on a Pi Zero W

The matrix lib starts a SCHED_FIFO priority-99 render thread that consumes ~80% of the single core continuously. The kernel's network softirqs and userspace threads (sshd, our curl calls) get whatever's left. In practice:

• SSH sessions can take a long time to complete the handshake while the service is running; usually they do eventually land. Persisting through one or two Connection closed retries works.
• HTTP timeouts are intentionally generous (60 s connect / 120 s read).
• We use one main thread for all rendering and network polling — no concurrent outbound calls. Weather and Spotify polls are sequenced so they never share the kernel's network stack at the same instant.

The CA bundle gotcha (read this if HTTPS is slow)

Debian's libcurl default sets CURLOPT_CAINFO=/etc/ssl/certs/ca-certificates.crt — a single ~200 KB file with 130+ CA certs. Every fresh curl_easy_init() re-parses the entire bundle to build a new SSL_CTX. On a Pi Zero ARMv6 with no crypto acceleration, that's ~1.4 s of user CPU per HTTPS call, which also stretches the wall-clock handshake long enough that strict servers (like Spotify's accounts endpoint) RST mid-handshake.

The fix is one line in src/net/http.cpp:

curl_easy_setopt(curl, CURLOPT_CAINFO, nullptr);
curl_easy_setopt(curl, CURLOPT_CAPATH, "/etc/ssl/certs");

OpenSSL hash-lookups only the specific issuer it needs to verify a chain from the hashed cert directory, instead of slurping the whole bundle. Drops per-call CPU ~10× (1.4 s → 0.13 s). Verification is still on. Confusingly, Debian's /usr/bin/curl is fast out of the box — it's only the libcurl C API that defaults to the slow bundle path.

If SSH genuinely won't land and you need to recover the Pi:

1. Mask the unit before next boot by editing bootfs/cmdline.txt (FAT partition, readable from a regular computer): append a space and systemd.mask=spotifydisplay.service at the end of the single line.
2. Reinsert + boot. The service is now masked; SSH stays responsive.
3. From SSH, sudo systemctl stop spotifydisplay, sudo rm /etc/systemd/system/multi-user.target.wants/spotifydisplay.service (bypasses the mask refusal), edit cmdline.txt back, reboot.

Disable the built-in audio driver

The matrix lib uses the BCM2835 hardware PWM for pixel timing, which conflicts with the Pi's built-in audio driver. Blacklist it once:

echo "blacklist snd_bcm2835" | sudo tee /etc/modprobe.d/blacklist-rgb-matrix.conf
sudo rmmod snd_bcm2835 || true

If you don't, the binary exits at startup with a message about the sound module being loaded.

Deploy updates

sudo systemctl stop spotifydisplay
git pull && make
sudo systemctl start spotifydisplay