solartools

macOS tools for monitoring a Logitech K750 solar-powered wireless keyboard's battery charge and ambient-light level.

The K750 reports its solar state over Logitech's vendor-specific HID++ protocol via the Unifying Receiver (USB 046d:c52b). These tools talk to the receiver through the IOKit HID Manager — no kernel extension or DriverKit entitlement required.

Components

Target	Type	Description
solarcli	CLI executable	Print the current reading once, or poll continuously on a timer.
solarbar	Menu bar app	Menu bar widget with a popover showing circular gauges for charge (0–100%) and ambient light (0–500 lux).
SolarCore	Library	Shared HID++ transport used by both executables.

Requirements

• macOS 13 or later
• Swift 5.9 toolchain (Xcode 15 or the matching Swift.org release)
• Logitech Unifying Receiver paired to a K750

On first run macOS will prompt for Input Monitoring permission. Grant it under System Settings → Privacy & Security → Input Monitoring. Only one process at a time can seize the HID++ collection, so don't run solarbar and solarcli --monitor simultaneously.

Build

swift build              # debug
swift build -c release   # optimized

Development / running from the repo

swift run solarcli --once
swift run solarcli --monitor --interval 30
swift run solarbar

Running via swift run is fine for iteration, but solarbar is a menu bar app — you'll get the best experience by packaging it as a real .app bundle (next section).

Packaging solarbar as a .app

All of the following can be done using the buildapp.sh script.

Details

SwiftPM produces a plain Mach-O executable. Wrapping it in an .app bundle lets you:

• move it to /Applications,
• hide the Dock icon cleanly (via LSUIElement),
• have macOS remember its Input Monitoring grant between builds,
• add it to Login Items so it starts automatically.

Run these commands from the repo root:

# 1. Release build
swift build -c release

# 2. Bundle skeleton
APP="SolarBar.app"
rm -rf "$APP"
mkdir -p "$APP/Contents/MacOS" "$APP/Contents/Resources"

# 3. Drop the executable in
cp .build/release/solarbar "$APP/Contents/MacOS/solarbar"

# 4. Write Info.plist
cat > "$APP/Contents/Info.plist" <<'PLIST'
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>CFBundleDevelopmentRegion</key>     <string>en</string>
    <key>CFBundleExecutable</key>            <string>solarbar</string>
    <key>CFBundleIdentifier</key>            <string>com.wyllys.solarbar</string>
    <key>CFBundleInfoDictionaryVersion</key> <string>6.0</string>
    <key>CFBundleName</key>                  <string>SolarBar</string>
    <key>CFBundleDisplayName</key>           <string>SolarBar</string>
    <key>CFBundlePackageType</key>           <string>APPL</string>
    <key>CFBundleShortVersionString</key>    <string>1.0</string>
    <key>CFBundleVersion</key>               <string>1</string>
    <key>CFBundleIconFile</key>              <string>AppIcon</string>
    <key>LSMinimumSystemVersion</key>        <string>13.0</string>
    <key>LSUIElement</key>                   <true/>
    <key>NSHumanReadableCopyright</key>      <string>Copyright (c) 2026 Wyllys Ingersoll. MIT License.</string>
</dict>
</plist>
PLIST

# 5. Ad-hoc codesign so macOS gives the bundle a stable identity
codesign --force --deep --sign - "$APP"

Key pieces of Info.plist:

• LSUIElement = true keeps the Dock icon from flashing at launch. The app also calls NSApp.setActivationPolicy(.accessory) at runtime, but setting it in the plist makes it clean from the first frame.
• CFBundleIdentifier gives the bundle a stable identity so macOS's TCC database remembers Input Monitoring grants across rebuilds. Change the string if you want your own namespace.

Install and run

mv SolarBar.app /Applications/
open /Applications/SolarBar.app

When macOS prompts for Input Monitoring, toggle SolarBar on under System Settings → Privacy & Security → Input Monitoring, then quit and reopen the app once.

NOTE If the app does not display any updates, click the light test button on the K750 keyboard to trigger an update.

Start automatically at login

Pick either:

• GUI: System Settings → General → Login Items & Extensions → Open at Login → + → /Applications/SolarBar.app.
• One-liner:

  osascript -e 'tell application "System Events" to make login item at end with properties {path:"/Applications/SolarBar.app", hidden:false}'

To remove later, delete the entry from the same Login Items pane.

Uninstall

rm -rf /Applications/SolarBar.app

Then remove it from Login Items and (optionally) revoke its Input Monitoring permission.

License

MIT. See LICENSE.