Bluetooth and external sound - TomBric/stratux-radar-display GitHub Wiki

External Sound output

You can connect your radar device with your intercom if it has an input for external audio (e.g. TQ KRT2 has one). This is possible on the Pi Zero with an external USB sound card. I used a simple "3D USB 5.1 Sound card" available for 4 Euro. The sound volume can be controlled via the option "-y 50" or can be modified with the pushbuttons under ->Status-> Net/Opt -> External Volume. The following link gives some good hints, which USB sound card can be used and it also shows how to solder it to the Pi Zero, if you do not want an adapter or space is an issue (https://www.raspberrypi-spy.co.uk/2019/06/using-a-usb-audio-device-with-the-raspberry-pi/).

If you are using a Pi3B or Pi4 for the radar-display you can use the builtin audio jack. To enable this, you have to specify "-mx PCM" (select mixer PCM) in stratux_radar.sh along with the option "-y 100" (for sound volume). If you are running the radar-display on the same Pi together with stratux this is currently not supported, since there are software conflicts.

Sound Output Level

Sound output of the audio jack as well as of the sound card described above has an output level for headphones. This is a level typically around 4 Vpp (Volts peak to peak). Check the documentation of your intercom/radio to find out the requested level for the external audio. Often the level requires an input of 1 Vpp. So you could set the output sound volume low, but this will not reduce the noise. My recommendation is to use a 10k Ohms multi-turn adjustable potentiometer as a voltage divider (see picture).

  • Connect the left connection of the potentiometer to the sound output
  • Connect the middle connection to your intercom/radio input
  • Connect the right connection to GND.
Spindelpoti

Now adjust the potentiometer so that the left to middle resistance is around 8 kOhms, the middle to right resistance around 2 kOhms. By this the output level is reduced with simple means.

Bluetooth devices

stratux-radar-display will automatically connect the your headset if their bluetooth is switched on. Please keep in mind that the bluetooth drivers on some pi-s have bugs. Sometimes pairing is not performed properly.

First, once you need to do the pairing of a new bluetooth device.

There are two options for pairing:

Option 1: Directly on the device via buttons:

  • Change to Status-Mode (long press middle button, to change from Radar-> Timer -> AHRS -> G-Meter -> Compass -> VSI -> Status)
  • Press "scan" (right button). The display now scans 30 secs for new devices. Set your headset as visible and it will be detected (For Bose A20 this is a 5 second press on the Bluetooth-Button until it flashes blue-red)
  • A list of detected devices is shown, press "yes" for the detected device. Sometimes you need to repeat the scan until your headset is detected.

Option 2: via ssh and bluetoothctl

   -> bluetoothctl
   -> scan on      set your device in pairing mode (for Bose A20, do a 5 sec press on the bluetooth button until it flashes magenta)
   -> wait till your device is displayed, this will look like:  
         [NEW] Device 04:52:C7:02:C0:01 Bose A20,              04:52:C7:02:C0:01 is the device id, which will be different for you
   -> scan off
   -> trust <device-id>   <replace with your device id>
   -> pair <device-id>, eventually your pin is requested (for Bose A20 enter "0000")
   -> connect <device-id>
If everything works fine, the pi displays connected and your device name.
   -> exit

The bluetooth configuration is now ready and each time the radar has your device in reachability, it will connect. On the display the bluetooth symbol will be visible in the right corner.

⚠️ **GitHub.com Fallback** ⚠️