Helmet Hacking – Making the Sena SMH-10 Bluetooth system work with helmet speakers or ear buds.

One of the features I wanted in a helmet comm system is the ability to use either earbuds or speakers in the helmet depending on what I am doing.   

For long distance rides, ear buds can be nice because they not only act as ear plugs, but also give much better audio.  But for quick runs up into the mountains, having some music without dealing with head phones would be nice.     

This is a compromise because nearly no one other than Interphone make a unit that will do both (and theirs requires a 50$ extension, too long, extension wire to do it).  Most have the speakers hard wired in to the unit, or are made only for headphones.

The stock SMH-10 mounting plate is like this:

With a hard wired speaker setup, and also the microphone mounted on the base itself.  Neither of which work for this helmet, or my use.

The Sena SMH-10 has a base option for headphones, but that makes it so you cant use in-helmet speakers.    That’s where the hacking comes in.

Step 1:

I ordered the A0304 Helmet Clamp kit for ~$30.  it comes with a remote mic that is easier to install in this helmet, and is made for earbuds and not in-helmet speakers as the original mount was.

I opened the mounting plate up to see if there was any internal circuitry differences between the speaker and the headphone base.   As expected, there were some resistors in line for the headphone one.  After doing some reading I figured on bridging over the resistors with a conductive pen to make the system compatible with the speakers again (and keep the volume where it should be).  I can always turn the volume down for the headphones.   And the conductive pen is completely reversible if I need.

I got the 304 base mounted to the helmet, and tested with ear buds.  OK… so it works.  Now lets get the speakers that are hard wire attached to the original base setup to work with this.

Step 2:

The 304 headphone base came with a nice 3.5mm extention stereo cable, that had a weather proof male end (its quite a nice cable!).   I choppped that portion of the cable off right before it got to the coiled portion.   I then went to the stock Sena mount and chopped the hard wired speakers off that.  

I then soldered up the wires together and tucked everything in clean in the helmet.   Giving the speakers now a 3.5mm connection to connect when I want them to be the audio source, or I can disconnect that and now can use any earbuds I want.

The biggest issue was the headphone extension wire, is comprised of Kevlar reinforced wires for all 3 runs.  and each strand was enamel coated for the wire.  To get the wires cleaned and separated I used a little bit of fire to burn off the enamel on the wires and then cut away the woven in Kevlar.  

Results:

Over all the install is very clean, and easy to work with.  All the wire and other stuff packed in the helmet is in areas not directly where my head is, so there is no uneven pressure or issues.  I haven’t tested the helmet on the road yet, going to try that today, but in static testing, the audio sound great, good and loud when needed, the mic isn’t in the way, and overall the whole system is very unobtrusive.

Now I Just need to get the cheek pads broken in a bit so I don’t look like my head is being crushed 🙂