PTT Bridge

Use the PTT button of a Bluetooth speaker-mic (like the Abbree) with DVSwitch Mobile, Zello and other radio apps on Android.

Español más abajo

Many Bluetooth speaker-mics sold for POC radios don't send a "PTT" that radio apps understand. The Abbree (it shows up as KST_vHMIC010), connected to a phone, sends its PTT over AVRCP as FAST FORWARD when pressed and REWIND when released. Radio apps ignore those keys, so the button does nothing.

PTT Bridge is a tiny app (≈40 KB, no libraries) that catches those keys and re-sends them as the PTT broadcasts radio apps listen to, with separate press and release:

Target	Press	Release
DVSwitch Mobile	org.dvswitch.intent.action.PTT_KEY_DOWN	org.dvswitch.intent.action.PTT_KEY_UP
EchoLink	com.echolink.ptt.down	com.echolink.ptt.up
VoxDMR	com.voxdmr.ptt.DOWN	com.voxdmr.ptt.UP
Zello	com.zello.ptt.down	com.zello.ptt.up
Generic POC apps	android.intent.action.PTT.down	android.intent.action.PTT.up

Broadcasts to known apps are addressed to their package: since Android 8 an implicit broadcast does not reach receivers declared in a manifest (EchoLink's are), and an addressed one even starts the app's receiver when it is closed.

Universal mode (default)

The bridge looks at the radio app in use (the one in front, or the last one used when the home screen is in front or the screen is off) and picks the best method by itself, with no setting to change when you switch apps:

1. Its PTT intent, if it has one (table above): works in the background and with the screen off.
2. Its on-screen PTT button, held down without root, if you taught it: an accessibility service keeps a finger on the button while the mic's PTT is pressed. Works with any app that has a hold-to-talk button on screen (Mumla, Peanut, BlueDV, DroidStar...). Needs the app in front and the screen on.
3. Root mode (optional), if set: hold a key code or a screen point.
4. Otherwise, every PTT intent known, for whatever app listens.

Teaching a button: in PTT Bridge tap Learn a PTT button and open the radio app within 5 s (or, with the radio app in front, expand the bridge's notification and tap Learn PTT button). A see-through blue layer appears: tap the app's PTT button on it. Done once per app.

The accessibility service (Settings › Accessibility › PTT Bridge) is what lets the bridge know the app in front and press screen buttons. It reads no screen content. Two Android quirks with apps installed from outside the Play Store:

• Android 13+ greys the switch out ("restricted setting"): open Settings › Apps › PTT Bridge, ⋮ menu › Allow restricted settings, then turn the service on.
• Updating the app turns the service off: turn it back on after each update.

Manual mode keeps the old behaviour: send to the ticked apps, plus root mode if set.

Compatibility

Found by decompiling each app, then tested on a OnePlus 8T (Android 16) by simulating the mic's keys over adb (cmd media_session dispatch fast-forward / rewind) and, for DVSwitch, with the real Abbree on the air.

App (version)	Works	How	Tested
DVSwitch Mobile 2.0.7	✅	own intent (also the generic one)	✅ on the air with the Abbree
EchoLink 1.8.10	✅	own intent, manifest receiver (setting "pttButton", on by default)	✅ receives DOWN/UP (startTx()/stopTX()), even with the app closed
VoxDMR 0.15.3	✅	own intent (also generic and Zello's). Set its PTT mode to Hold to transmit: in hybrid a short press latches the TX and ignores the release	✅ on the air with the Abbree (TG 214)
Zello	✅	com.zello.ptt.* (documented by Zello)	not tested
BlueDV AMBE 1.0.119	✅ root	physical key in the foreground: 27 (CAMERA), 131 (F1), 132 (F2), 134, 135, 139, 142, 228–230, 261, 276, 278, 280, 294, 300, 301, 305	✅ root key mode, code 27: "PTT ON" 73 ms after press, "PTT OFF" 24 ms after release
Peanut 1.81	✅ root	key learned in its setup, in the foreground	not tested (same mechanism as BlueDV)
Mumla 3.7.3 (Mumble)	✅	on-screen PTT button (set Transmission mode: Push to talk), taught in the universal mode; or root key	✅ on the air with the Abbree, without root
DroidStar	✅ root	only its on-screen TX button: root screen-point mode (turn off its TX toggle setting so the button is hold-to-talk); the no-root taught button should work too	✅ root mode on the air with the Abbree; no-root not confirmed yet

Install

Download the APK from Releases and install it. Android 5.0 or newer.

Use

1. Pair the speaker-mic with the phone as usual.
2. Open PTT Bridge and tick the app(s) to send the PTT to (DVSwitch comes ticked). The bridge keeps running in the background with a notification.
3. Use your radio app normally and press the mic's PTT.

Notes:

• Only one app gets the media buttons at a time. Fully close any other app that also handles the mic's buttons.
• In DVSwitch, use the mic for audio only. Do not select it in DVSwitch's own Bluetooth PTT menu: that one is for BLE mics and keeps failing to connect ("failed to connect", GATT 133) to a classic Bluetooth mic.
• On the Abbree, P1 sends AT+BLDN, which Android itself handles as "redial the last number". No app can stop that, so don't use P1.
• + / − are the normal phone volume.
• If the release is ever lost (mic out of range, flat battery), the bridge releases the PTT on its own after 180 s.
• DroidStar stays on "connecting" without any message when no vocoder is loaded: load one in its settings first.

How it works

The keys arrive through a MediaSession. The tricky part is that Android delivers media keys to the app that most recently started playing among those currently playing. DVSwitch starts playing audio the moment it transmits, so it would steal the keys and the REWIND (release) would go to DVSwitch: the PTT would never release. To prevent that, the bridge keeps a looping, silent AudioTrack (media usage, no audio focus requested, so it interrupts nobody) and restarts it every 3 s, and every 0.7 s while transmitting. The broadcasts use FLAG_RECEIVER_FOREGROUND; without it they arrived ~0.5 s late.

What the Abbree sends

Measured with btmon on Linux and on Android:

Connected profiles	PTT	P1	+ / −
A2DP + AVRCP + HFP (a phone)	AVRCP FAST FORWARD on press (tap + ~0.5 s hold), REWIND on release	HFP AT+BLDN	volume
HFP only	HFP AT+BLDN on press and again on release	—	AT+VGS

Android TV

Works on Android TV too (tested on a Chromecast with Google TV, Android TV 14): the Abbree pairs with the hands-free profile, its PTT reaches the bridge and DVSwitch Mobile transmits with the Abbree's microphone (turn on DVSwitch's Voice Call audio source). But the Chromecast does not play call audio to a Bluetooth headset: the received audio is routed to it and never comes out (its audio system lacks that path; it even crashed once while trying). So on a Chromecast the Abbree works as mic + PTT, not as speaker. The bridge shows up in the TV's app list, and its screen has an Open a radio app row, because phone apps like DVSwitch are not listed in the TV launcher. Install the APKs with adb; turn on the accessibility service from adb or Settings › Accessibility.

Other speaker-mics

If your mic sends other keys, run adb logcat while pressing it and open an issue with what you see, or send a pull request: the key handling is in BridgeService.onKey() and the targets in BridgeService.TARGETS.

Build

./gradlew assembleRelease

Without a release keystore the build is signed with the debug key.

License

Apache 2.0. See LICENSE.

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Español

Usa el botón PTT de un micro-altavoz Bluetooth (como el Abbree) con DVSwitch Mobile, Zello y otras apps de radio en Android.

Muchos micros Bluetooth pensados para radios POC no mandan un "PTT" que entiendan las apps de radio. El Abbree (aparece como KST_vHMIC010), conectado a un móvil, manda el PTT por AVRCP como AVANCE RÁPIDO al pulsar y RETROCESO al soltar. Las apps de radio ignoran esas teclas y el botón no hace nada.

PTT Bridge (en español, "PTT Puente") es una app mínima (≈50 KB, sin librerías) que recoge esas teclas y las reenvía como los avisos de PTT que escuchan las apps de radio, con pulsar y soltar por separado.

Modo universal (por defecto): el puente mira qué app de radio usas (la de delante, o la última si estás en el escritorio o con la pantalla apagada) y elige solo el método: su intent de PTT si lo tiene (DVSwitch, EchoLink, VoxDMR, Zello: funciona con la pantalla apagada), o mantener pulsado su botón de PTT de la pantalla sin root si se lo enseñaste (Mumla, Peanut, BlueDV, DroidStar...). Para enseñarlo: en PTT Puente toca Aprender un botón PTT, abre la app de radio antes de 5 s y toca su botón de PTT en la capa azul.

Necesita activar el servicio de accesibilidad de PTT Puente (no lee el contenido de la pantalla). En Android 13+, si el interruptor sale gris: Ajustes › Apps › PTT Puente › menú ⋮ › Permitir ajustes restringidos. Al actualizar la app, Android lo desactiva: vuelve a activarlo.

Uso

1. Empareja el micro con el móvil como siempre.
2. Abre PTT Puente y marca a qué app(s) mandar el PTT (DVSwitch viene marcada). Se queda funcionando en segundo plano con una notificación.
3. Usa tu app de radio con normalidad y pulsa el PTT del micro.

Avisos:

• Android solo entrega los botones a una app a la vez. Cierra del todo las demás apps que también usen los botones del micro.
• En DVSwitch, usa el micro solo para el audio. No lo elijas en su menú de PTT Bluetooth: es para micros BLE y con uno de Bluetooth clásico solo da "failed to connect" (GATT 133).
• En el Abbree, P1 manda AT+BLDN, que Android interpreta como "rellamar al último número". Ninguna app puede evitarlo: no uses P1.
• + / − son el volumen normal del móvil.
• Si alguna vez se pierde el soltado (micro fuera de alcance, sin batería), el puente suelta el PTT solo a los 180 s.

Otros micros

Si tu micro manda otras teclas, mira adb logcat mientras lo pulsas y abre un issue con lo que salga, o manda un pull request: las teclas se tratan en BridgeService.onKey() y los destinos están en BridgeService.TARGETS.