I’m in the process of reworking the interface box between the amateur radio HTs on our bikes and our helmet-mounted earbud & mic lashup. Mary needed a new helmet before I got the new interface ready, soooo there’s an adapter cable in the middle.
This time around, the helmet cable uses a male USB-A connector, rather than a female 6-pin Mini-DIN PS/2 keyboard connector. Either one is cheap & readily available as assembled cables, which gets me out of soldering teeny little connector pins. These days, though, USB cables are more common.
The motivation for a non-latching, low-extraction-force connector at the helmet is that when (not if) you drop the bike, the helmet doesn’t tie your head to the bike and snap your spine. Falls on a recumbent are much less exciting than on an upright bike, but you still want the bike to go that-a-way while you go this-a-way. Been there, done that.
The old helmet cable connector: female 6-pin mini-DIN. The wire color code is not standardized. Viewed from rear of female connector or the front of the male connector, with the key slot up:
ear com - Gn 5 |_| 6 K - ear hot
mic com - Or 3 key 4 Y - mic hot
gnd - Bn 1 2 R - gnd
The new helmet cable connector: male USB-A. Mercifully, they standardized the wire colors. Looking at the front of the male USB-A connector with the tab down and the contacts up, the pins are 4 3 2 1:
- 1 – R – ear hot
- 2 – W – mic hot
- 3 – G – mic com
- 4 – K – ear com
The female USB-A connector is exactly the same.
That arrangement should produce the proper twisted pairs in a USB 2.0 cable, but all the USB cables I’ve seen so far lay all four wires in a common twist inside the shield. Maybe it’s the cheap junk I buy, huh?
It’s worthwhile to scribble some color in the background of the trident USB symbol so it’s easier to mate the connectors.
Memo to Self: verify the connections & proper operation before shrinking the tubing!
The Smell of Molten Projects in the Morning 
So, when some “helpful” person plugs that gadget into a PC, what blows up first? :)
Well, the helmet has the earbud across the +5V supply, so the hub should power-fault. Worst case, there’s a nasty pop as the earbud burns out.
Plug a USB device into the interface and nothing happens: a mic driver just can’t handle USB negotiations!
And, should somebody be carrying the pocketful of gender benders required to wedge either of ’em into a PC, I think the same thing happens: helmet power-faults and interface shrugs.
I suppose I should mill the trident out of those pockets and engrave something meaningful. Not that anybody pays any attention to warning signs or anything …
Good idea for the connection. I use multiple radios in my convertible and have been thinking about a box to mix audio to my earbuds with a priority scheme to handle multiple incoming transmissions. Are you aware of any schematics or IC’s that might be a good basis for a design?
Thanks for this site. First thing I read in my feed when I see new activity.
A 4-to-1 analog multiplexer controlled by simple rectifier audio detectors ought to work, but I’d be tempted to throw a microcontroller into the mix: sample the incoming audio channels with ADCs, do some simpleminded DSP, then figure the priority logic in firmware. Pains me to say it, but an Arduino Pro Mini has almost everything you’d need except the analog MUX.
Don’t know of a design out there, but the GPS+voice circuit I’ve been using shows that the analog part isn’t all that complex.
If you’re not getting a post a day, then something’s fallen off the feed along the way! [grin]
Good thoughts. I’m more comfortable in the digital domain so I’d love to do it with a microcontroller. Once you’ve got bits all kinds of things can happen. I hadn’t thought of doing my own sampling with a general purpose processor and I’ll definitely look into that.
I have looked at some specialty chips but haven’t found one that seems to solve the whole problem. I’ve found some that bring in multiple analog signals and turn them into bits with control pins that can control the output from an outboard microcontroller but I keep getting stuck on signal detection. Without having played with it yet, I was thinking something along the line of looking for a minimum average amplitude in the digital signal. Can you say more or cite some sources on “rectifier audio detectors?” Just something for me to get the concept and start working out my circuit.
Thanks for the pointer to your GPS+voice circuit. Looks like a great source to mine for ideas.
And yeah, I get something in the feed pretty much every day. I love seeing you solve problems and quantify things. Keep it up. You have fans! :)
Which go out of production on a distressingly regular schedule. For one-off projects maybe that’s OK, but I have a bunch of those around here that depend on long-gone parts…
That’s little more than a diode and a capacitor; think peak detector or half-wave rectifier and you’ve got the essence.
But I think you could sample a communications-grade channel at maybe 1 kHz, because all you’re looking for is energy. Aliasing and suchlike absolutely don’t matter: those bits will never become audio again (the audio output comes from the analog MUXes). You get the bits, take the absolute value (relative to the idle-channel level), compare it with a squelch level, and that gives you a simpleminded activity detector. Keeping the sampling rate low means that a cheap microcontroller can handle several audio inputs and diddle the MUX controls.
Which is not to say somebody couldn’t complexicate the design with a real DSP, but …
Thanks for the good words!
That’s everything I need for a running start.
Thanks! This is going to be fun.
Just wanted to thank you for the help on my priority multiplexer project.. I’ve got an Arduino reliably detecting audio on multiple sources and have some 4066 bidirectional switches on the way to see how they work for audio switching.
Excellent! Glad to hear it’s working!
Those should work for communications-grade audio, but they have a very high and surprisingly variable on-resistance with a 5 V supply. Keep the audio amplitude down, don’t use them as power switches, and they’ll do fine.
Let us know how it plays …
I’ll watch that. I’ll report back and, as always, if you think of alternative ways to switch the audio, I’m all ears.
Thanks again!
Hi, just found yer site, and am finding it to be interesting, humorous, and potentially helpful. Feel buttered, yet? :) We ride motorcycles, and have purchased a helmet headset from some company that uses firewire (I think) connectors to mate the cable/radio to the mic and speakers. Same concept as yours, I guess, but these seem to fail too often. (Thankfully they had a good warranty.) I intend to read all your entries, but in the event that I don’t find what I’m looking for, maybe you’ll be willing to help?? thanks in advance.
We use Cobra walkie talkie things, a PTT button on the handlebar, there’s a helmet mounted mic and a speaker for each ear. I’m confident with my soldering skills; but will USB give us enough wires?
The larger pointed-rectangle connectors have 6 conductors and the tiny dented-rectangle connectors have 4 conductors. The pictures in the Wikipedia article may help identify what you have.
USB cables have 4 conductors, which provides one pair for the mic and one for the speaker. If the radio has stereo sound (perhaps for an FM tuner?), then USB won’t work; maybe you could do without stereo. In any case, you would need another connector for the PTT switch.
If the radio has a single connector for everything, you could build an adapter cable between the radio and your custom helmet / PTT connectors. That’s what I did with the Wouxun: the plug plate holds those two audio plugs in place, with pigtails from the GPS case for everything else.
The USB connectors hang out in mid-air behind our helmets, which probably won’t withstand your use. The next time I rebuild a helmet, I will mount the plug directly on the helmet to stabilize the joint and get it away from the top bar of the seat frame. You have more room on a motorcycle, so perhaps putting the joint close to your waist (on a belt hook?) would work better.
Ride on…
Hello again. thanks for your reply, I’ve been checking on some things, trying to formulate an intelligent response. Here goes.
The Cobra radio has one connection, 2.5mm. The PTT is connected to the cable by what looks to be a 3.5mm plug. The headset has 2 speakers, and I believe they are stereo. There is a short cord coming out of the helmet, ends in a female firewire, 6 pins. The connector cord is coiled, which is nice, has a tail going off for PTT, one going off for the radio and one going off for a cell phone, which we tried to use with mp3. The sellers of the headset said that using mp3 with that would burn out “something” I believe that they meant it would affect the radio at some point. http://www.sierra-mc.com/proddetail.asp?prod=IMC-HS-430
At one point, both headsets were shorting/staticky, seemed to be at the junction of the 2 firewires, and since the headsets had a 2 year warranty, we sent them back. New headsets installed, mine is still going good, but my wife’s has been sent in a couple more times. I don’t know how she’s harder on it, but she was using her mp3 a lot…until we heard about the burning up issue.
There is no priority device built in…if the Cobra radio is plugged into the cell phone plug, it transmits as open mic, which is quite annoying to the others in the group!
so what do I want? I want to know how to test the headset, to determine where the faults are, I thought that I could test the PTT with my ohm meter setting on the multimeter, but I got nothing from that. Is there a way to use both mp3 and Cobra w/o “burning up” the units? I’m guess that if so that is going to be above my skill set.
If it would help, I could send a pic or 2 of these items, and if you don’t want to spend any time thinking about me and my problems here in MN, just say so! Thanks. Mick
Wow, they must be multiplexing the daylights out of those three wires to the radio. I’d expect something like this:
Judging from the photo, they simply connect the MP3 audio directly to the radio audio and route the result to the speakers, which seems misguided; I don’t know how MP3 stereo could possibly work in that configuration. Given their “burns out” warning, “misguided” may be an understatement.
I’m sure they don’t provide the pinouts for all the connectors, but you can probably conjure up matching connectors (perhaps from eBay by cannibalizing Firewire PC brackets and audio extender cables?) for all the ends, measure the resistance from all the pins to all the others, then figure out which ones get intermittent. It’ll be a major puzzle and if measuring wire continuity doesn’t reveal the problem, then there’s nothing else I can suggest.
I went to great lengths to not have unnecessary connectors in my GPS+Audio setup. Their lashup seems to have at least two connectors that aren’t needed, plus plenty of delicate joints with no strain relief bushings: I’m not surprised things quickly fall apart.
Wish I could be of more help, but I rolled my own because I wasn’t satisfied with anything I could find!