Use your Mac hardware like a modular synth!

A suite of commands like accelerometer, microphone, bandpass, keyboard-brightness, screen-brightness, and more that can be linked together using UNIX pipes.

All tools input and output a standardized mono audio signal that represents their sensor input/output values.

Quickstart

git clone https://github.com/pirate/mac-hardware-toys
cd mac-hardware-toys

uv sync
source .venv/bin/activate

### Examples

# flash your screen according to your microphone input
microphone | screen-brightness

# play a sine wave tone based on your screen lid-angle
lid-angle | speaker

# flash the keyboard according to your heartbeat (keep your wrists on palm rests)
accelerometer | metronome | keyboard-brightness

# see more detail about any given signal by piping it into visualizer
microphone | visualizer
sine 1000 | visualizer
gyroscope | tee >(speaker) | visualizer

Tools

accelerometer

• Purpose: read Apple SPU accelerometer and emit mono signal.
• Args: --rate <hz> (<= 800), --axis x|y|z|mag, --raw.
• Notes: requires root; when run from a terminal it auto-prompts via sudo.

ambient-light

• Purpose: read ambient light sensor and emit tone mapped from low light to high light.
• Default mapping: 500 Hz -> 5000 Hz and low volume -> high volume as light goes 0% -> 100%.
• Args: --rate, --low-hz, --high-hz, --low-volume, --high-volume, --json.
• Notes: requires root; when run from a terminal it auto-prompts via sudo.

lid-angle

• Purpose: read lid angle sensor and emit tone mapped from lid closed to open.
• Default mapping: 500 Hz -> 5000 Hz and low volume -> high volume as angle goes --angle-min -> --angle-max.
• Args: --rate, --low-hz, --high-hz, --low-volume, --high-volume, --angle-min, --angle-max, --json.
• Notes: requires root; when run from a terminal it auto-prompts via sudo.

gyroscope

• Purpose: read fused orientation (accel+gyro, Mahony AHRS) and emit tone mapped from the selected orientation axis.
• Default mapping: 500 Hz -> 5000 Hz and low volume -> high volume as selected axis angle maps to 0..360.
• Args: --rate, --low-hz, --high-hz, --low-volume, --high-volume, --json, --axis roll|pitch|yaw, --decimate.
• Notes: requires root; when run from a terminal it auto-prompts via sudo.
  • roll/pitch are absolute to gravity; yaw is relative and can drift without magnetometer.

microphone

• Purpose: capture mono mic signal and emit stream.
• Args: --rate <hz>, --block-size <frames>.

metronome [bpm]

• Purpose: emit metronome pulses; with piped stdin it auto-detects/follows BPM.
• Args: optional bpm, --rate (fixed mode), --pulse-ms, --tone-hz, --level, --accent-every, --accent-gain, --block-size, --count, --min-bpm, --max-bpm, --detect-low-hz, --detect-high-hz, --self-echo-ms, --follow, --debug, --raw.

---

bandpass <low_hz> <high_hz>

• Purpose: realtime cascaded high/low-pass filter.
• Args: positional cutoffs or --low/--high, --chunk-bytes, --raw --rate.

frequency-shift <factor>

• Purpose: best-effort realtime frequency scaling, takes a scalar multiplier like 0.1~1000.
• Args: factor, --chunk-bytes, --raw --rate.

volume-shift <gain>

• Purpose: scalar amplitude gain.
• Args: gain, --chunk-bytes, --raw --rate.

heartbeat

• Purpose: emit BPM/confidence JSON lines from incoming signal (typically bandpassed). When piped onward, it passes the signal through on stdout and writes JSON to stderr.
• Args: --interval, --window-seconds, --emit-final, --chunk-bytes, --raw --rate.

---

speaker

• Purpose: play incoming stream on default output device.
• Args: --device-rate, --block-size.

visualizer

• Purpose: terminal waveform + level monitor.
• Args: --fps, --window-seconds, --chunk-bytes, --raw --rate.

keyboard-brightness

• Purpose: beat-follow keyboard backlight control.
• Args: --send-hz, --fade-ms, --gain, --attack-ms, --release-ms, --baseline-ms, --decay-per-s, --debug, --as-root, --pulse, --on-time, --off-time, --set.
• Notes:
  • --set=<0..100> without --pulse sets brightness and exits immediately (ignores stdin).
  • --pulse=<N> ignores stdin and pulses N times; --set controls pulse max brightness.

screen-brightness

• Purpose: beat-follow display brightness control.
• Args: --send-hz, --min-level, --max-level, --gain, --attack-ms, --release-ms, --baseline-ms, --decay-per-s, --debug, --no-restore, --pulse, --on-time, --off-time, --set.
• Notes:
  • --set=<0..100> without --pulse sets display brightness and exits immediately (ignores stdin).
  • --pulse=<N> ignores stdin and pulses N times; --set controls pulse max brightness.

fan-speed

• Purpose: signal-follow fan RPM control (both fans in sync by default; beat-alternating optional).
• Args: --send-hz, --min-rpm, --max-rpm, --min-frac, --max-frac, --pulse-depth, --couple, --alternate, --input-map, --beat-threshold, --beat-hold-ms, --gain, --attack-ms, --release-ms, --baseline-ms, --decay-per-s, --debug, --no-restore.

---

Example Usage

Heartbeat from accelerometer:

accelerometer | bandpass 0.8 3 | heartbeat

Ambient light as signal source:

ambient-light | visualizer

Lid angle as JSONL:

lid-angle --json

Gyroscope fused orientation as JSONL:

gyroscope --axis roll --json

Music-reactive keyboard + speakers:

microphone --rate 44100 \
  | tee >(keyboard-brightness --send-hz 30 --fade-ms 20) \
  | volume-shift 0.8 \
  | speaker

Metronome to speakers:

metronome 120 | speaker

Auto-follow metronome from mic input, emits a metronome tone in sync with the beat of whatever audio is playing:

microphone | metronome | speaker

Auto-follow metronome from accelerometer, driving keyboard pulses:

accelerometer | metronome | keyboard-brightness

Metronome driving keyboard pulses:

metronome 120 | keyboard-brightness

Heartbeat telemetry while still driving keyboard brightness:

accelerometer | heartbeat | keyboard-brightness

Set keyboard backlight to 100% and exit:

keyboard-brightness --set=100

Pulse keyboard 5 times (1.2s on / 5.5s off) at 100%:

keyboard-brightness --pulse=5 --on-time=1.2 --off-time=5.5 --set=100

Set screen brightness to 40% and exit:

screen-brightness --set=40

Pulse screen brightness 3 times:

screen-brightness --pulse=3 --on-time=1.2 --off-time=5.5 --set=100

Metronome driving fan pulses:

metronome 120 | fan-speed --send-hz 4 --alternate --input-map beat --min-frac 0.30 --max-frac 0.70

Slow sine fan sweep (sync L/R):

sine 0.1 | fan-speed

One source, multiple sinks:

accelerometer \
  | bandpass 0.8 3 \
  | tee >(keyboard-brightness) \
  | frequency-shift 1000 \
  | volume-shift 0.8 \
  | tee >(speaker) \
  | visualizer

---

Notes

• accelerometer requires root (AppleSPU HID access) and will auto-reexec through sudo by default.
• ambient-light, lid-angle, and gyroscope do the same for AppleSPU HID access.
• Set MSIG_AUTO_SUDO=0 to disable auto-reexec and only print rerun guidance on stderr.
• microphone/speaker depend on sounddevice + PortAudio runtime.
• Keyboard/display brightness tools need supported hardware/permissions.
• keyboard-brightness uses the bundled Apple Silicon KBPulse binary at lib/KBPulse (arm64).
• fan-speed uses AppleSMC private IOKit APIs on Apple Silicon; writing fan targets typically requires sudo.
• frequency-shift is intentionally lightweight and artifact-prone at extreme factors.

Stdio Audio Format

All stream tools read/write:

• header: MSIG1 <sample_rate_hz>\n
• payload: little-endian float32 mono samples

Most processors also support raw float32 input via --raw --rate <hz>.

---

Why?

It's fun. Here are some ideas to get started:

• make your keyboard lights flash for security alerts using Security Growler
• make your keyboard flash right before your display is about to sleep
• make your keyboard flash on incoming email
• make your keyboard flash to the beat of music
• make your keyboard flash when your boss's iPhone comes within bluetooth range

---

Related Projects

• https://github.com/olvvier/apple-silicon-accelerometer IOReg accelerometer reading code
• https://github.com/EthanRDoesMC/KBPulse/ keyboard brightness code for M1, M2, M3, etc. macs
• https://github.com/maxmouchet/LightKit
• https://github.com/tcr/macbook-brightness
• http://stackoverflow.com/questions/3239749/programmatically-change-mac-display-brightness
• https://web.archive.org/web/20110828210316/http://mattdanger.net:80/2008/12/adjust-mac-os-x-display-brightness-from-the-terminal/
• http://osxbook.com/book/bonus/chapter10/light/
• https://github.com/samnung/maclight/blob/master/lights_handle.cpp
• http://www.keindesign.de/stefan/Web/Sites/iWeb/Site/iSpazz.html the OG
• https://github.com/bhoeting/DiscoKeyboard