Umar "2E0UMR" Munir's Blue Dmod Is a Simple, Low-Cost Bluetooth Data Modem for the Ham on a Budget

Radio amateur Umar "2E0UMR" Munir has built a Bluetooth data modem for various digital modes, using low-cost off-the-shelf components controlled by an Arduino-compatible microcontroller — with plans afoot to turn the Blue Dmod into a single-PCB implementation.

"On [the] market there are lots of options for sound card-based data modems, like Signalink, Digirig, and lots of DIY and cheap modems," Munir explains of his inspiration for the project. "I haven't seen any Bluetooth based audio data modem apart from Mobilinkd which is unfortunately Bluetooth serial port TNC [Terminal Node Controller]. In order to keep the cost to minimum I got together components I already had, [I] just had to order the microcontroller as I didn't have any small form factor microcontrollers."

The Blue Dmod is built around a cheap BT002 Bluetooth audio module, with Munir connecting the radio's microphone input to the module's left audio channel, the radio's audio output to the module's microphone input, and the module's right audio channel to an Arduino-compatible microcontroller. There's a relay for push-to-talk (PTT) functionality, as "not all radios like transistor/MOSFET-based PTT," Munir explains.

"To keep [it] all simple I used [an] RJ45 port to connect [the] radio to [the] modem," Munir writes. "It [is] easy to make RJ45-based cables [rather] than using any special connector. I have tested the 'Blue Dmod' with Wouxun KG-UV9D, Wouxun KG-UV9K, and TCA/PRC 152 [radios]. On TCA/PRC 152 I had to add a ferrite core on high power."

More information on the project is available on Munir's website; an initial schematic and the project's source code are available on GitHub under the reciprocal GNU General Public License 3.