[Android] Bluetooth hardware PTT button support

[kenw6ire]

It would be great if the app supported Bluetooth PTT buttons (example: PRYME BT-PTT-Z/BT-PTT-ZU) and Bluetooth hand mics (example: PRYME BTH-550-MAX/BTH-600-MAX)

The two types of devices both operate in slightly different ways:

For the PTT-buttons only:

• This is a BTLE device has the Bluetooth friendly name PTT-Z and can be used for PTT on either Android or IOS.
• Sends one 'Notify' event on button press, and another notify event on button release.
• Service: 0xFFE0
• Characteristic: 0xFFE1
• Value: 1 = Pressed, 0 = Released
• Service UUID: 0000ffe0-0000-1000-8000-00805f9b34fb
• Characteristic UUID: 0000ffe1-0000-1000-8000-00805f9b34fb

For the hand mics:

• These devices each essentially contain two different Bluetooth devices: the first is a conventional Bluetooth device using the Bluetooth Headset Profile for audio and the Handsfree Profile for PTT on Android. This device has the Bluetooth friendly name BTH-PTT. *HFP AT commands for Android -PTT pressed AT+XEVENT=TALK,1\r -PTT released AT+XEVENT=TALK,0\r -AUX BUTTON/SOS pressed AT+XEVENT=SOS,1\r
• The second device is a BTLE button which is available for pairing only after the BTH-PTT is paired with the phone and which can also be used for PTT. It is identical to the PTT-Z device above except that it uses the service UUID 28393551-5345-5209-FD67-45287C0BDAC5.

[VanceVagell]

This is a really good write-up, thank you for all the details to help make it easier to build. I'd love this as well so I can more easily use my kv4p HT in the car!