Radio Interface for Phone/Tablet

Posted on February 22, 2017 Updated on February 12, 2017

The MicroAvionics MM005 powered radio interface required a little extra effort to get working good with my tablet and phone. My Note 5 did not like the phone adapter, apparently the 1k Ohm resister across the microphone was insufficient to make the Note think a microphone was connected. This was not a huge problem since I planned on making my own cable anyway.

My Nexus 7 ( 2nd gen 2013) microphone input did not like the high level output by the MM005 from the phone or the AUX OUT port. The level was so high that it caused lots of clipping resulting in some horrible sounding recordings. My Note 5 did not seem to care and recorded well from both ports. The cable I made for the Nexus 7 included an additional resister to convert the line level output of the MM005 to microphone level. Maybe not the best way to deal with this but was certainly the easiest. The resisters fit inside the audio connector ends resulting in a nice clean looking cable. 

The other end of the cable goes to a dash mounted 3.5mm TRRS / USB port.
A short audio cable connects the tablet. 

To power the phone and tablet I used a ZeroLemon USB charger. I picked this particular model because it did not cause RF interference with the radio. Every other charger I tried caused tons of RF noise when tuned to around 132Mhz, the closest airport to me is CMH on 132.7 so it was only by chance that I even noticed this problem. I did take the charger apart so I could hard wire the power, I did not want to rely on it staying plugged into a cigarette lighter.

Not decided how our where I will mount this adapter but I’m thinking of just drilling a couple holes and using a zip tie.