OpenMatrix is a lightweight iOS app for sending a still image to an iDotMatrix display over Bluetooth LE. It currently encodes images as 32 × 32 RGB frames.
- Install the app on your iPhone and tap Scan. On the first scan, iOS should ask to allow Bluetooth access; approve the prompt.
- Turn on the iDotMatrix display, tap Scan, and select it. The scan lists nearby BLE devices even when the display does not advertise an iDotMatrix name.
- Choose an image and tap Send to Display. If the display cannot be reached, OpenMatrix retries the image transfer. Tap Retrying... to cancel.
- To use Shortcuts, add Send Image to Display and provide an image. The action uses the display selected in OpenMatrix; it can run without opening the app after that initial setup.
- Adjust saturation, contrast, sharpness, orientation, or horizontal mirroring in Image adjustments. The numeric fields accept values outside the slider range; all adjustments are saved and also apply to Shortcuts images.
- Enter a Last.fm API key and username, select Sync Now Playing Cover Art, or add that action in Shortcuts to send the current track's cover to the display. A failed display connection is retried; tap Retrying... to cancel.
OpenMatrix checks Last.fm for track changes every 30 seconds while it is open. It also requests an iOS background app refresh after the app is backgrounded. iOS chooses when (or whether) to run that refresh, so background cover updates are best-effort, not immediate or continuous. Last.fm must report a track as currently playing and provide cover art for it.
OpenMatrix waits for a Bluetooth write acknowledgement when the display supports acknowledged writes. The display does not report whether an image was successfully rendered, so an acknowledged transfer is not proof that the screen updated.
The app's background Bluetooth capability allows Shortcuts to attempt the send without presenting the app. iOS may still limit background execution or Bluetooth connectivity depending on device state and system policy.
If Bluetooth access was previously denied, enable it for OpenMatrix in Settings > Privacy & Security > Bluetooth, then return to the app and scan again. The app shows Bluetooth startup, permission, and scan status below the display list.
The app icon uses the blue dot.radiowaves.left.and.right mark from the
in-app header. The asset catalog provides a white-background light icon and a
dark-gradient icon for iOS dark appearance and Home Screen icon customization.
Every push builds an unsigned iOS archive, packages OpenMatrix.ipa, and uploads
it as the OpenMatrix-unsigned-ipa workflow artifact. The workflow can also be
started manually with Build unsigned iOS IPA under the Actions tab. Download
the artifact from the completed workflow run. The IPA is not App Store-signed;
installing it requires a compatible sideloading/signing workflow.
The Xcode project is generated from project.yml using
XcodeGen.