Connect TH-D74 to Raspberry PI via Bluetooth

To get started, it's easiest to use the GUI to connect to the TH-D74. At the end of that process, you'll see a message that says "No usable services". After that, open a terminal and run rfcomm to connect and create the serial port /dev resource.

Here's the script I use to do that:

#!/bin/bash
# connect to /dev/rfcomm0
# MAC address of the TH-D74 (on the D74, in Menu 9-3-5)
# Channel 2 (found by running `sdptool records 24:71:89:98:63:B9`
sudo rfcomm connect 0 24:71:89:98:63:B9 2

More details can be found on K1CHN's website at https://www.k1chn.com/posts/winlink-th-d74a-now-with-more-bluetooth/