WatchPanel

Turn an old Android tablet into a wall panel that shows a live camera feed and a web dashboard at the same time.

Built for and tested on a Samsung Galaxy Tab A 2016 (SM-T280) running Android 5.1.1 — a 1.3 GHz Cortex-A7 with 1.5 GB RAM. It is deliberately built to work on hardware that modern kiosk apps have left behind.

• Camera pane — live RTSP with hardware H.264 decode, sub-second latency, and automatic reconnect. Any RTSP source; nothing is vendor-specific.
• Feed buttons — switch between cameras. Hidden automatically with only one.
• Web pane — any URL: Home Assistant, Grafana, a weather page, or your own.
• Presence dimming — the front camera wakes the screen when someone approaches, using frame-differencing rather than an ML model.
• Kiosk mode — becomes the launcher, survives reboot, and can be switched off again from inside the app.
• Portrait or landscape — one layout tree, set to match your bracket, with the camera above/left of the web pane or below/right of it.
• Tap the picture to toggle sound. Muted by default; the state is announced briefly on screen, since there is no permanent speaker icon.

A Galaxy Tab A 2016 in portrait: dashboard on top, live camera below.

Build

export JAVA_HOME="/Applications/Android Studio.app/Contents/jbr/Contents/Home"
./gradlew :app:assembleRelease
adb install -r app/build/outputs/apk/release/app-release.apk

Builds out of the box with debug signing. For release keys, create keystore/signing.properties (gitignored):

storeFile=keystore/my.jks
storePassword=...
keyAlias=...
keyPassword=...

Why the code looks like this

Constraint	Consequence
SC8830 has no HEVC decoder	libVLC, not ExoPlayer, so there is a software fallback. H.264 decodes in hardware via OMX.sprd.h264.decoder.
API 22 predates APK Signature Scheme v2	enableV1Signing true is mandatory — a v2-only APK will not install.
targetSdk 22 on purpose	Keeps install-time permissions; no runtime grant flow for the camera.
1.3 GHz Cortex-A7	Presence detection is luma frame-differencing, well under 1 ms/frame at 320×240. ML Kit would manage a few fps and pin a core.
No AppCompat	Native Theme.Holo.NoActionBar.Fullscreen; only libVLC's transitive androidx.annotation is pulled in.

Settings

Reached with the gear icon in the corner of the camera pane. Everything lives in one JSON blob in SharedPreferences, so it survives app upgrades.

Camera feeds

Name and URL per button; add and remove rows freely. Any URL libVLC can open works — RTSP is what the app is shaped around, and what gives sub-second latency. Reolink cameras use:

rtsp://user:pass@HOST:554/h264Preview_01_main   full resolution
rtsp://user:pass@HOST:554/h264Preview_01_sub    lower resolution

The button strip hides itself automatically when only one feed is configured.

Dashboard

Setting	Notes
Web page URL	Anything the WebView can render — Home Assistant, Grafana, your own page
Auto-reload interval	Seconds; 0 disables. Set 0 for Home Assistant, which updates over a WebSocket and only pays for the reload
Ignore SSL certificate errors	For sites whose chain the device's trust store cannot build. Enable only for a host you control — see Notes for old devices

Layout

Setting	Notes
Orientation	Portrait, Landscape or Auto. A wall bracket has one orientation; Auto lets a knock rotate the display
Camera position	Top/left or bottom/right of the web pane
Camera pane size	Percent of the screen: height in portrait, width in landscape
Scale video to fill the pane	Crops the overflow so the picture covers the pane. Off letterboxes the whole frame. A 16:9 feed in a 4:3-ish pane loses noticeable width when on
Video zoom	100 leaves scaling to libVLC. Higher zooms explicitly, relative to the source's native size — the fallback for streams that never report their geometry, where the automatic fit has nothing to compute from

Button colours

Ten swatches plus a hex field with a live preview, for the selected feed button and the others. Label text flips between black and white automatically based on the background's luma, so light colours stay readable.

Screen & presence

Setting	Notes
Dim after	Seconds of no presence before dimming; 0 keeps the screen on permanently
Awake / dimmed brightness	0–100. Dimmed 0 is effectively off — see How dimming works
Wake on front-camera motion	The camera is opened only while dimmed, and released the moment the screen wakes
Motion pixel threshold	Per-pixel luma delta counting as changed. Lower is more sensitive
Motion area trigger	Fraction of sampled pixels (per mille) that must change. Raise it if sensor noise wakes the panel on its own
Stop the stream while dimmed	Saves heat and bandwidth on a 24/7 device; costs a second or two on wake

Stream tuning

Setting	Notes
Network caching	RTSP jitter buffer in ms. Lower means less lag and more stutter
RTSP over TCP	Recommended. UDP drops frames on busy Wi-Fi

Kiosk

Run as home screen makes the app the launcher, disables Back, and sends you to Android's home-app picker. Turn it off in the same place to get the normal home screen back — the HOME filter lives on a toggleable activity-alias precisely so this does not require a reinstall.

How dimming works

The screen is never actually turned off. screenBrightness goes to ~0 behind a black overlay, so waking is instantaneous — no display power-on latency, no lock screen. It is an LCD, so there is no burn-in risk from staying on.

The front camera is opened only while dimmed — the only time the answer matters — and released the moment the screen wakes.

Notes for old devices

• Trust store: Android 5.1's root CAs are from 2015. Sites chaining to newer roots may fail; the app has an opt-in SSL override for a host you control.
• WebView version matters far more than the OS version. Lollipop can run WebView up to ~95, which is the difference between "no modern JS" and "Home Assistant works".
• Battery: a permanently-charged old tablet will swell eventually. A smart plug on a duty cycle is the usual mitigation.

How this was built

Vibecoded with Claude Code. Claude wrote effectively all of the code across one long session; I specified what I wanted, designed the dashboard in Sketch, ran every build on the actual tablet, and said when things were wrong.

Licence

MIT — see LICENSE.