Motorola MU350R remote PTT

Hello All,

I am interested in the new Motorola MU350R Bluetooth FRS radio. In my particular application, I want to pair it with my SENA SMH10 helmet bluetooth headset & intercom. The setup would be about perfect if it were not for PTT button; i.e., activating the PTT on the MU350R is not practical while navigating the woods on a snowmobile (and VOX, even if supported, is not going to work in this application either).

Motorola makes a bluetooth PTT button for the MU350R; however, it costs more than the radio itself! (A two pack of MU350R radios can be had for $120.00ish, and a single BT PTT button is $85.00ish…unreal).

The truth is, I don’t need a wireless/BT PTT button, I would be fine with a wired PTT button affixed to the handlebars (the setup of the SENA SR10 bluetooth two-way adapter is great…but if the radio can do BT then one would hope that they wouldn’t require the expense of the SENA SR10).

The question is does anybody know if a remote PTT could be wired to the accessory port of the MU350R while maintaining microphone/speaker communications over bluetooth to the headset? My understanding of remote PTT buttons isn’t great, but as near as I can tell, they are normally just a switch inline with the microphone on a wired headset which isn’t applicable for my situation. Anybody know if an appropriately sized resistor (in place of the microphone) could be put inline with a remote PTT switch wired into the accessory port of the MU350R just for the purpose of triggering PTT while still communicating over bluetooth to the headset?

Short of that, I would have to open the radio and “remote” the physical PTT button somehow (and that opens of a legal can of worms as to whether or not that is an “internal” modification to the radio thus voiding its FCC certification)…

Thanks for any thoughts or comments,


Hey Jeff,

The truth of the matter here is that what you’re asking about/for makes sense there really is not a good way to do it however. Your understanding of the how the PTT button is correct is that with a wired solution the button completes the circuit of the mic and radio loop.

However, and this is just my understanding, when the radio is paired with a Bluetooth headset the PTT button is still active allowing for audio from the Bluetooth mic to be transmitted when depressed. Moving that ability to a remote wired PTT button would require some software reconfiguration to recognize the remote PTT as the internal signal.

When a Bluetooth device is active the software translates the PTT button as an enable to transmit audio signals being sent from the Bluetooth mic. Without a paired device the button operates the internal mic only. Activating the external accessory jack often overrides both those commands and typically will expect audio coming from an external source and not the Bluetooth device.

Technically speaking, you can route some new wires from the internal PTT to a remote button to act as the internal loop but that would not be the best solution and would void the warranty as you would have to open the case.

I would not be surprised if in the future there is a new dongle that is available that acts as the PTT button and also has the Bluetooth transreceiver built into that module so you can talk/listen through it rather than rely on the Bluetooth built into the radio. (Seriously a good idea right there, someone should rush out and start building on that idea. Just remember who gave you the idea first!) :slight_smile:


Thanks for the reply. You pretty much summed things up to the same conclusion that I had come to on my own (but I just didn’t want to admit to defeat). Disappointing that the PTT wasn’t given more thought on such a capable consumer grade radio given the obvious features that one would want to take advantage of given the Bluetooth capabilities (then again, I think that the Yaesu VX 8R, a $500 HAM HT, has the same “design flaw”). I’ll have to decide if I want to crack the case open and hardwire a remote PTT – not so worried about voiding Motorola’s warranty – slightly more disappointed that “mod’ing” the radio (in any way) would likely [albeit absurdly] invalid its FCC compliance under the strict letter of the law. Looks like I have three options:

  1. Crack open the case and design a hardwired remote PTT switch for it.
  2. Wait and hope that Motorola either enhances the design of the radio in a sensible way or dramatically drop the price of their Bluetooth PTT button.
  3. Buy the SENA SR10 bluetooth two-way radio adapter – probably the best all around solution in that I would have complete control over which radio to use (and allowing me to sled with my HAM radio if I wanted to). But it is also the most costly…

Thank you for your time and interest!

-Jeff kc7zfa

Hey Jeff,

I’m with you on the ‘There has to be a way…’ and technically speaking cracking the case open and modifying the PTT isn’t illegal as you are not modifying the radios itself rather just the accessibility to the unit you may loose the water resistance of the radio by cracking the seals (if any). But, to get back to how the heck would I do this. It should be pretty simple.

All the normal PTT button does is close and open circuit. So to add to the existing PTT circuit would require is a set of wires to an external switch that would close the circuit remotely. Which would allow the software to still interpret the circuit as closed. (Electricity doesn’t care one button from the next, as long as it has a place to go!). So connecting directly to the button terminals should do the trick. Then all you need is some wire, heat shrink tube, and an external SPST switch to act as your PTT button.

However, and this is eluding to the idea I had earlier. You can always buy a Bluetooth adapter and modify it to work for this situation. So the Bluetooth adapter connects to the microphone/speaker jack to send and receive signals then the Bluetooth adapter allows you to connect the headset. They made just such a thing for older cell phones so people could use new Bluetooth headsets with older phones. Now, the only difference here is that in a phone the transmit happens all the time where as you would want it to only happen on command. So simply breaking the circuit on the wires that go to the headset jack and adding a button would do the trick and break/complete the circuit as needed.

I think I can mock something up here in a week or so. Of course, please feel free to do your research. The main idea here is that the adapter handles the connection to the headset both RX/TX and then the wire that would attach to the cellphone headset jack attaches to the radio. So the only addition would be a toggle switch in that wire bundle that connects the two (radio and bluetooth adapter).

One other note, in the adapter idea the radio itself doesn’t need to have bluetooth built in rather the adapter supplies that. However, one downside to the adapter handling that interaction is that it would require its own power source.

Just a last minute thought.