Radio noise suppression & bluetooth headset

Ground Loop isolation

Testing the new bluetooth output from the radio I had some ground loop noise.

Two options:

   - Isolate the 5v feed to the bluetooth board

   - Isolate the audio connection from the radio to the bluetooth board

I went for the second with a cheap off the shelf component which installs between the radio cable and the bluetooth card. No power required - inside are a couple of audio 1:1 transformers for left & right channels.

Does the job - audio is now crystal clear. 

Headset Mod

I bought a pair of Sena SMH5 intercom units, designed for installation inside a motorcycle helmet. Selection of SMH5 vs 10 is a combination of price, due to being an older model, nice prominent rotary volume control and physical size. They will also work when charging via a 5v USB cable which means my pet hate of flat batteries is not a problem.

SMH5's can pair to each other - for standard intercom functionality as well as mobile phones and receive a bluetooth audio input. I think although have not tested they should be able to also share the bluetooth signal - so the single transmitter installed in the radio should provide audio to both passengers.

The first one is installed on a Howard Leight L0f earmuff. Selection being a combination of price and quality - they are thinner than my existing wired earmuffs but perfect for modding. The SMH5 sticks to the outside and cables routed over and sewn to the headband, speakers stick inside to the earmuff padding.

I didn't want to detach the speaker cable, it is very flexible and thin & dont fancy re-soldering the stereo wiring inside - hence routing it outside the headband, this approach also means I have not damaged the SMH5 in any way - warranty FWIW intact.

The loose cable is for the microphone arm to be installed later.

Update - completed these headsets much later,  sometimes life just happens and the car takes second place!