As seen on Daring Fireball

This small driver enables the Griffin PowerMate, a nifty little device from days gone by. What does the PowerMate do? It is a knob that you can twist or that you can press. That's it. It also has a blue LED in the base that can change intensity based on what you're doing.

When it was released, it was intended to assist video and audio production by adding a scrollable knob to your desktop. Of course, modern controllers exist that offer many more literal bells and whistles, but there is something... quaint... about this early device.

To install, download the latest release from the releases tab. Download and open the DMG, and then drag PowerMate Agent to your Applications folder. Then, launch PowerMate Agent. Of course, it won't do anything without a PowerMate, so go dig around in your junk USB drawer and dust it off! You will see a new item in your top menu to control the behavior of the PowerMate. If you want it to launch when you start your Mac, add it to your startup items.

brew tap jameslockman/tap
brew install --cask griffin-powermate-agent

Uninstalling with Homebrew is just as easy

brew uninstall --cask griffin-powermate-agent

Once installed, PowerMate Agent will appear in your menu bar.

If the menu bar is hidden by the notch on a laptop display, then PowerMate Agent will appear in your dock.

The PowerMate acts as a scroll control, so if the active window or control has a scroll option, turning the dial will scroll the window or increase/decrease selected value. You can reverse the scroll direction if you don't like the default scroll direction.

The PowerMate can also act as a mouse button. A momentary push of the button acts as a mouse click when in scroll mode. A long-press of the button acts as a right-click. You can also change the behavior so that a long-press acts as a double-click, switches between scroll and audio mode, or runs a shell command.

Run script mode: Select "Run script" under Long press in the menu, then open Configure Scripts... to enter up to two shell commands. A regular long press runs the first command; holding Shift while long-pressing runs the second. Any command that works in Terminal works here — open, osascript, custom scripts, etc. This makes it easy to trigger two frequently-used actions (launching apps, running automations, controlling other tools) without any extra hardware.

Audio mode: Enable "Audio mode" in the menu and the knob adjusts system volume while the button toggles mute. When audio mode is active, the LED brightens and dims in sync with the amplitude of whatever is playing through your speakers. A short sound cue confirms the switch — up when entering audio mode, and down when returning to scroll. The menu bar icon's ring turns blue while audio mode is active so you can tell at a glance which mode you're in.

Volume control works exactly like the physical keyboard volume keys:

• Turn — standard volume step, identical to pressing F11/F12.
• Shift + turn — fine volume step, identical to pressing Shift+Option+F11/F12. Useful for precise adjustments.
  • Note: You can swap the fine and normal volume controls in the menu if you prefer a slower turn rate.
• Fn + turn — temporarily flips the mode. If scroll mode is active, Fn switches to audio mode; if audio mode is on, Fn switches back to scroll mode.

In scroll mode, turning the knob scrolls vertically and Shift + turn scrolls horizontally. Enable Default to horizontal scroll in the menu to swap the axes — turning without a modifier scrolls horizontally, and Shift + turn scrolls vertically. Reverse scroll direction reverses whichever axis is currently active.

Press and turn — hold the button and turn the knob to skip tracks in the current media player. Turn clockwise to skip to the next track, counter-clockwise to go back.

The click action in audio mode is configurable via Click in audio mode in the menu. Choose Mute/unmute or Play/Pause as your primary action. Holding Shift while clicking activates the alternate action — so you can reach both without changing the menu setting.

The VU Meter (LED amplitude display) can be toggled independently of audio mode via its own menu item.

Long press can also be configured to toggle between modes directly, which is handy if you switch often and prefer not to use the Fn key.

Menu icon	Dock Icon	What it means
		No PowerMate connected to the computer.
		Scroll Mode active
		Audio Mode active

Notch-aware Dock icon: On MacBooks with a camera notch, the menu bar icon can be pushed behind the camera housing when many items are present. PowerMate Agent detects this automatically and shows a Dock icon so you can still access the menu. The Dock icon reflects the same three states (not connected, scroll mode, audio mode) as the menu bar icon. It disappears from the Dock when the menu bar icon is visible again.

All configuration choices (scroll direction, audio controls, long-press action) are saved automatically and restored the next time the app launches.

On first launch, PowerMate Agent will prompt you to grant Accessibility permission. When you first enable audio controls, it will also prompt for Audio Capture permission. Both are required for full functionality.

Pretty simple, eh?

Mode-change sounds can be replaced with your own audio files. Place them in scripts/Sounds/ before building:

AIFF or WAV are recommended. If a file is absent the built-in system sound is used instead.

When the Dock icon is visible (notch fallback), you can supply your own icons. Place ICNS files in scripts/Icons/ before building:

1024×1024 source PNGs can be converted to ICNS with sips and iconutil (both included with macOS). If a file is absent the SF Symbol fallback is used for that state.

A small macOS driver that opens the Griffin PowerMate (VID 0x077d, PID 0x0410) over USB HID, reads its 6-byte reports, and exposes button and rotation events so you can map them to actions (e.g. scroll, click, media keys).

The device reports on the bus but does nothing by default on macOS; this library seizes the device and delivers events to your app.

• Byte 0: Button state — 0 = released, 1 = pressed
• Byte 1: Rotation delta — signed; positive = clockwise, negative = counter‑clockwise (typically ±1 to ±7 per report). The device does not report speed directly; the driver derives rotation rate (deltas per second) from the time between reports.

cd /path/to/USB
swift build
swift run PowerMateDemo

With the PowerMate plugged in, turn the knob or press the button; the demo prints events. Stop with Ctrl+C.

PowerMateAgent turns the knob and button into keyboard/scroll events that any application receives (browser, editor, etc.):

• Rotation → vertical scroll (or horizontal when Default to horizontal scroll is enabled), or Up/Down arrow keys when a menu (or submenu) is focused, or system volume in audio control mode (standard step; hold Shift for fine step; hold Fn to temporarily flip modes). Hold Shift to scroll the alternate axis in scroll mode.
• Press and turn → skip to the next or previous track in the current media player.
• Click (short press) → left mouse button (at cursor), or Return when a menu is focused (chooses the highlighted item), or mute/unmute / play/pause in audio control mode (configurable; Shift alternates between the two actions).
• Long press → right mouse button, or configurable to double-click, toggle audio/scroll mode, or run a shell script.

Menu detection uses the Accessibility API: when the focused UI element is a menu or submenu, rotation sends arrow keys and click sends Return. A long-press also enters a fallback “menu mode” (arrow keys until click or 5-second timeout) if Accessibility is not enabled.

Audio mode — enable “Audio mode” in the menu, hold Fn to temporarily flip, or configure long press to toggle. A “Tink” plays when entering audio mode; a “Pop” plays when returning to scroll. Fn always XORs the current mode without a sound cue since it's held, not toggled.

LED VU meter — when audio control mode is active, the LED brightness tracks the RMS amplitude of the system audio output in real time using AudioHardwareCreateProcessTap.

Persistent settings — scroll direction, audio mode, and long-press action are remembered across launches.

The LED throbs while you turn and goes dim when idle; full brightness while the button is held.

swift run PowerMateAgent

On first run, macOS will prompt for Input Monitoring permission. Grant it in System Settings → Privacy & Security → Input Monitoring and add (or enable) the Terminal or the built executable, then run the agent again.

To run in the background: swift run PowerMateAgent & or run the built binary ./.build/debug/PowerMateAgent and add it to Login Items if you want it to start when you log in.

To create a signed, notarized app (or installer) so others can use it without security warnings, see DISTRIBUTION.md. You’ll need an Apple Developer account; users will need to grant Input Monitoring, Accessibility, and (if using audio controls) Audio Capture once on first use.

In your app’s Package.swift (or Xcode: File → Add Package Dependencies):

dependencies: [
    .package(path: "/path/to/USB"),  // or your clone URL
],
targets: [
    .target(name: "YourApp", dependencies: ["PowerMateDriver"]),
]

import PowerMateDriver

let driver = PowerMateDriver()

// Optional: use closures for simple mapping
driver.onRotate = { delta, rate in
    // delta > 0 = clockwise, delta < 0 = counter-clockwise
    // rate = deltas per second (nil on first report); use for speed-dependent mapping
    // e.g. scroll: CGEventCreateScrollWheelEvent(..., delta * lineHeight)
}
driver.onButtonDown = { /* e.g. simulate click or toggle */ }
driver.onButtonUp = { }

// Or use the delegate for all events
driver.delegate = self  // implement PowerMateDriverDelegate

driver.start()
// Keep run loop running (e.g. main thread in an app)

• **PowerMateEvent.buttonDown** / **buttonUp** — knob pressed / released
• **PowerMateEvent.buttonClick** — short press and release (under longPressThreshold).
• **PowerMateEvent.buttonLongPress** — press held at least longPressThreshold, then release.
• **PowerMateEvent.rotate(delta: Int, rate: Double?)** — delta is the signed step count (e.g. +1, -2); rate is derived rotation speed in deltas per second (nil on first report).

Set **longPressThreshold** (default 0.4 seconds) to tune what counts as a long press. Use **onClick** and **onLongPress** (or the delegate) for separate handling.

Use driver.isConnected to see if the device is currently opened.

The base has a blue LED you can use for feedback. Control it only when the device is connected (isConnected == true).

• **setLEDBrightness(_ value: UInt8)** — static brightness 0–255 (0 = off).
• **setLEDPulseAsleep(_ on: Bool)** / **setLEDPulseAwake(_ on: Bool)** — turn the built‑in pulse when “asleep” or “awake” on or off.
• **setLEDPulseMode(table:op:arg:)** — custom pulse: table 0–2, op 0 = slower, 1 = normal, 2 = faster, arg 1–255 for op 0/2.

LED commands use USB vendor control requests (same protocol as the Linux driver). They return true if the command was sent successfully. If the USB device is busy (e.g. another process has it open), LED calls may fail.

• Scrolling: In onRotate, create a scroll wheel CGEvent (e.g. CGEventCreateScrollWheelEvent) and post it, or feed the delta into your own scroll logic.
• Click: In onButtonDown / onButtonUp, create and post a mouse click CGEvent, or call your own click handler.
• Media / other: Map onRotate and onButtonDown to whatever you need (e.g. volume, key equivalents).

Posting events may require Input Monitoring (or Accessibility) in System Settings → Privacy & Security for your app.

1. Unplug and replug the PowerMate, then run your app again.
2. Quit other software that might be using the PowerMate (e.g. old PowerMate apps).
3. The driver uses kIOHIDOptionsTypeSeizeDevice so it takes exclusive access; only one process can use it at a time.

• macOS 13+
• Swift 5.9+

• Linux PowerMate driver (report format: byte 0 = button, byte 1 = rotation)
• Resurrecting the Griffin PowerMate on Linux
• Apple IOKit HID: IOHIDManager, IOHIDDeviceOpen, IOHIDDeviceRegisterInputReportCallback

Press and turn — track skip: holding the button while turning the knob now skips tracks in the current media player. Clockwise skips to the next track; counter-clockwise goes to the previous track.

Simplified volume control: volume now uses the same NX media key events as the physical keyboard volume keys, which works reliably across all output devices (built-in speakers, Bluetooth headsets, HDMI monitors, USB audio). Turning without modifiers is a standard step (same as F11/F12); holding Shift gives a fine step (same as Shift+Option+Volume). The velocity-based automatic precision tiers and the volume OSD have been removed in favour of this simpler, more consistent approach.

Velocity-based volume control: turning the knob slowly now adjusts volume in fine (~1%) increments, a medium turn uses quarter-step increments, and a fast turn uses standard volume steps — automatically, with no modifier keys required. Shift and Shift+Option still work as explicit overrides to force a specific precision.

Fine volume controls:

• Holding Shift while turning the knob in audio mode now adjusts volume in quarter-step increments, similar to using shift-option-volume up/down. The On Screen Display will appear and you will get audio cues that the volume has changed.
• Holding Shift-Option while turning the knob in audio mode now adjusts volume in small, perceptually-consistent increments. The On Screen Display will NOT appear, and you will not get any audio cues that the volume has changed. Know that the volume will change in 1% increments across the full range of values.

Fine volume control: holding Shift while turning the knob in audio mode now adjusts volume in small, perceptually-consistent increments. The step size adapts across the volume range so it always takes approximately two turns per hardware step, regardless of the current volume level.

Play/Pause as a click action: the click action in audio mode can now be set to Play/Pause (in addition to Mute/unmute) via the new Click in audio mode submenu. Holding Shift while clicking swaps to the alternate action — so if your primary action is Mute, Shift+click plays or pauses, and vice versa.

VU Meter toggle: the LED VU meter can now be enabled or disabled independently of audio mode via a dedicated menu item.

Help dialog: a Help... menu item summarises all controls and modifier combinations, with a clickable link for feedback and bug reports.

Menu reorganised: the menu is now more compact — Audio mode → VU Meter → Click in audio mode → Reverse scroll direction → Long press → Configure Scripts → Help → Quit.

Configure Scripts improvements: script fields are now multi-line, support paste and undo (Cmd+V / Cmd+Z), expand ~/ paths automatically, and show placeholder text when empty.

Added script execution mode: configure up to two shell commands via Configure Scripts... in the menu, then set Long press to "Run script". Long press runs the first command; Shift + long press runs the second.

Added release version check. If we detect a new version, then a menu will appear under Configure Scripts... to guide the user to the releases page for the latest version.

Reduced CPU usage in audio VU meter mode. The LED is now updated at ~25 Hz instead of at the audio hardware rate (~86–170 Hz), and updates are skipped entirely when amplitude is steady. Accessibility API calls for menu detection are now cached, reducing IPC overhead during fast knob rotation.

Fixed cursor drift when turning the knob — the HID manager now seizes the device at the manager level so macOS no longer stays attached and moves the cursor. Thanks to Matt Hocker for identifying the root cause and providing the fix.

Fixed display wake cycle on sleep: the driver now fully releases the PowerMate when the display sleeps, preventing the device from triggering USB remote wake and causing the screen to turn back on moments later.

PowerMate no longer prevents device sleep.

Added notch-aware Dock icon fallback: when the menu bar icon is hidden behind the camera housing, a Dock icon appears automatically and reflects the current state (not connected, scroll mode, audio mode). Uses custom ICNS files for all three Dock icon states.

Menu bar icon now indicates when there is no PowerMate connected.

Added audio cue for when mode changes. Icon now has blue ring when in Audio Mode. Audio Mode is now called... Audio mode.

Added LED VU meter (tracks system audio amplitude via AudioHardwareCreateProcessTap), Fn-key mode flip, long-press toggle for audio/scroll mode, Audio Capture permission handling, blue menu bar icon when audio mode is active, and custom sound file support. Updated app identifier string.

Added audio controls (volume + mute), settings persistence, and accessibility permission check. Also made scrolling smoother.

Initial release. Includes scrolling and clicking, with optional double-click or right-click for long presses.