Das blinkenlight

Drive a Blink(1) mk3 USB LED to display real-time GPU and CPU utilisation on an Apple Silicon Mac.

LED	Metric	Colour	Idle → Full
1 (top)	GPU Active Residency	Magenta (val, 0, val)	Dark → Bright
2 (bottom)	CPU usage	Cyan (0, val, val)	Dark → Bright

Install

Prerequisites

• macOS on Apple Silicon (uses powermetrics GPU sampler)
• blink1-tool — brew install blink1
• uv — brew install uv (or any Python package installer)

1. Allow passwordless sudo for powermetrics

sudo visudo -f /etc/sudoers.d/powermetrics

Add this single line (replace cls with your username):

cls ALL=(root) NOPASSWD: /usr/bin/powermetrics

Save and exit. Verify:

sudo -n /usr/bin/powermetrics --samplers gpu_power -i 1000 -n 1

2. Install blinkenlight

uv tool install .          # from a local checkout

This puts the blinkenlight command on your $PATH.

3. Test manually

blinkenlight run

[info] blinkenlight starting (pid 12345)
[load] GPU  12.3% → rgb(31,0,31)  | CPU   8.5% → rgb(0,21,21)

Press Ctrl-C — both LEDs turn off cleanly.

4. Install as a background service

blinkenlight install

This generates a launchd plist (with the correct paths resolved automatically), copies it to ~/Library/LaunchAgents/, and loads it. It will start on every login and restart on crash.

Usage

blinkenlight run          # start the monitor (foreground)
blinkenlight install      # install + start the launchd agent
blinkenlight uninstall    # stop + remove the launchd agent
blinkenlight status       # check if the agent is loaded

Managing the service

blinkenlight status       # is it running?
blinkenlight uninstall    # stop and remove
blinkenlight install      # (re)install and start

View logs:

tail -f /tmp/blinkenlight.log    # stdout
tail -f /tmp/blinkenlight.err    # stderr

Development

uv tool install -e .      # editable install for development
blinkenlight run          # run directly