Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
I designed the GPS+Audio case around the TinyTrak3+ board in my radio, which has two square, blue-plastic trimpots. The case worked fine for that board. Then I printed the case for the next bike and that TT3+ didn’t slide neatly into place:
TinyTrak3+ trimpot overhang
Turns out that one of the three TT3+ boards uses plastic trimpots and the other two have metal trimpots bent to fit the existing holes (so they’re not a drop-in replacement), with a very slight overhang beyond the edge of the PCB.
So I attacked the case with some riffler files and carved a notch above the PCB slot. No pictures of that, lest you think I’m a butcher of lovely 3D printed objects. Next time: build the notch into the case’s solid model.
Most likely, this is the only instance of those pots causing anyone a problem…
The Wouxun KG-UV3D is advertised as a “dual band” radio, but it has only one hardware receiver: in TDR mode (there is no explanation of what TDR means, so there may not be an English equivalent; I suspect it’s not Time Domain Reflectometry) with two frequencies / channels displayed, the first to receive a transmission produces audio output until that signal stops, regardless of what happens on the other frequency / channel. In contrast, the ICOM Z1A and W32A radios we were using had two hardware receivers and the audio output was the sum of the two signals, with independent volume controls.
That wouldn’t matter, except that I monitor the E911 dispatch channel while riding, so that I know when an emergency vehicle will be coming along my route: distracted drivers are bad enough, but a distracted driver dodging an ambulance is really bad. The E911 transmitters have punchy audio compared to anything else, so it’d be nice to turn down the dispatcher’s level compared to the relatively quiet voice + APRS signals on the other channel.
No can do.
The KG-UV3D also requires much higher audio on the mic input than the Z1A for the equivalent output. Contrary to that schematic, I’m now running the op amp gain at about 4.5 (13 dB) instead of 1.6 (4 dB): it’s a 100 kΩ feedback resistor. That puts it on a par with the E911 audio, but it’s still somewhat quiet.
The TinyTrak3+ board produces audio tones through a 4-bit binary resistor network that feeds into a 220 kΩ resistor in series with the 10 kΩ trimpot that sets its output level. Cranking that pot all the way up produces roughly the same volume as the +13 dB helmet mic audio. If I increase the mic gain any further, however, I should also increase the TT3+ audio output, which means reducing the 220 kΩ resistor on the TT3+ board. The TT3+ doc advises:
Some mobile radios require more audio drive than TinyTrak3 puts out. If audio levels are too low, even with the R6 pot set to maximum, consider replacing the 220K R5 with a 100K resistor or shorting jumper. This should allow for about double the audio range.
Dunno if that means another 3 or 6 dB or what, but it might come in handy.
However, increasing the mic gain has the disadvantage of causing more wind noise: it’s always there and high mic gain makes it much worse. The foam balls over the mics work well, but the voice volume drops off dramatically as the mouth-to-mic distance increase; about half an inch is a good distance. So there’s an upper limit on mic gain.
I’ve also increased the earphone attenuation, with a 150 Ω resistor in series with the earbud, to give the receiver volume control more useful range.
It’s workable as it stands and the many APRS receivers have no trouble decoding the packets, so all this is in the nature of fine tuning. I do miss the dual audio outputs, though…
Our Larval Engineer has been diligently procrastinating on her summer project to add ground effect lighting to her longboard. I’m hereby depriving her of the opportunity to learn enough OpenSCAD to build a case from scratch:
Longboard Ground Effect Lighting Case – exploded view
This is upside-down from its in-use position, but she’ll have it in this orientation on the bench. Four 10-32 screws clamp the whole affair together and hold it to a bottom aluminum plate with threads to suit; that plate also gets bolted between the longboard and the rear truck.
The general idea is that four 2 A·h lithium prismatic cells live in the bottom slice with their protection circuit, sandwiched between two aluminum plates that should protect them from all but catastrophic impact. The circuit board (which ought to be a PCB, but we’ll go with hand wiring for the first iteration) gets clamped in the recess between the two upper slices, above the upper aluminum plate. A polycarbonate sheet on top provides visibility for the Arduino blinky LED inside and shows off the circuitry to one and all.
I think a ridge on each long wall should suffice to hold the cells against the end wall; we don’t have the cells in hand to figure that out yet. She gets to add internal partitions, cable cutouts, and suchlike.
Oh. “Ground effect lighting” means ten RGB LED strips glued under the longboard deck. Her innovation is to make the LED color depend on the speed, which can range upward to scary-fast. It’s a simple matter of software, using a Hall effect sensor for input. This will look much better after dark, but she’s pretty much nocturnal anyway.
After a few sessions of soldering-and-checking, it looks good:
HT-GPS PCB – cabled in place
The yellow wires on the far right are temporary power connections; battery power enters through the contact studs in those large holes that press against the radio’s battery terminals. The cable in the lower right is the mis-color-coded USB cable that carries audio to & from the earbud & mic on the helmet. Not all the pads have components; I didn’t use all the parallel bypass cap locations because I wasn’t up for protracted self-resonance measurements.
The TinyTrak3+ cable solders into the empty DB9 footprint over on the left. I must cannibalize that from the ICOM IC-Z1A interface in Mary’s bike after the next Wouxun KG-UV3D arrives; with any luck, there’ll be a rainy day or two for that work.
The as-built schematic (clicky for more dots), which is pretty close to the original intent:
Schematic – Wouxun HT GPS+Voice Interface – August 2012
Based on those measurements that suggest spacing the plugs at 11.5 mm on center, I tweaked that parameter in the source code there and printed another one, just like the other one. Actually, I printed four of the fool things this time:
Wouxun plug plates – 11.5 mm fixture
With the plugs in the gluing fixture and the fixture in the vise, a ring of epoxy around the threaded sides holds them in place:
Wouxun plug plate – wired
A trial fit in the Wouxun KG-UV3D shows that the jacks prefer the 11.2 mm spacing I measured on the Wouxun headset, but they’ll accept plugs on 11.5 mm centers. I don’t know if that’s a real specification difference, a manufacturing tolerance, or what.
FWIW, I’ve been using snippets of that cable forever, because it’s perfect for this application: two unshielded conductors and three more inside a braid, supple as a snake. It’s surplus, of course, with a gorgeous push-lock plug (and the jack!) on one end that must have cost a fortune… and which I’ll never to use for anything. Got two of them, just in case.
Mushing an epoxy putty turd on the top anchors everything in place and protects the wires:
Wouxun plug plate – epoxy cap
In point of fact, the cable insulation isn’t anchored inside the blob and a minor tug could pull it loose. There will be a bit of slack at the case to allow for unlatching it from the radio, but the lashup will spend its entire life inside a snug pouch, so it shouldn’t come to any harm. We shall see.
Try as I might, I cannot uncover a definitive answer to this simple question: What’s the center-to-center spacing of the mic and earphone jacks on the side of Kenwood and Wouxun HTs?
The usual searches produce answers like 11 and 12 mm, both of which are obviously wrong, as can be determined eyeballometrically just by holding a scale against the plugs.
Based on measurements I made on a Wouxun headset, the yellow plug mounting plate put the plugs on 11.2 mm centers and they fit into the KG-UV3D radio; it’s been working fine ever since.
However, having just measured a speaker/mic and a headset, both from Kenwood, I come up with 11.5 mm. Frankly, I trust the Kenwood hardware a bit more: the plugs seem more rugged and the overall production values are higher.
The calculation is simple: measure the pin diameters, then subtract half their sum from the outside distance across the pins. Cross-check by adding half the sum to the inside distance between the pins, which should give the same answer. It helps if the pins are actually round.
The jacks in the Kenwood and Wouxun radios have enough compliance to accept either a Wouxun or a Kenwood headset plug without complaint. Maybe it doesn’t matter?
Despite that, I made another gluing fixture with 11.5 mm spacing:
Plug alignment plate – 11.5 mm spacing
Those are 0.1 inch grids; it’s a little bitty block of smoke-gray polycarbonate from the scrap heap. The plugs are nominally 3.5 mm (which is not 1/8 inch in this universe) and 2.5 mm, with clearance drills #28 and #39.
Then I tried poking those 11.2 mm spaced plugs, now firmly epoxied in place in the yellow plate, and guess what: they don’t fit, no how no way. That’s not surprising, because there’s no compliance on either side of the joint and the plugs aren’t on the right centers for the fixture. Makes for a good No-Go gauge, I suppose.
However, I think I’ll tweak the solid model spacing to 11.5 mm and run off another plug mounting plate for the next radio.
FWIW, our ICOM IC-Z1A HTs use a sensible 10.0 mm spacing and that old fixture worked fine.
For this version of the contacts (the old version is there) that make the GPS interface look like a standard Wouxun lithium battery, I left a bit more of the slot on the brass screw heads and increased the recess depth to compensate:
HT-GPS Case – Battery contacts
The nuts all have fancy nickel plating, with washers & ring lugs silver-soldered in place:
HT-GPS PCB – battery contact parts
The trial fit looks OK:
HT-GPS Case – PCB and battery contacts – end view
I even found the cutest little flat 1/4 inch wrench that fits 4-40 nuts, so I can do a better job of crunching the PCB between the nuts. That excess screw length has got to go, too…
The Smell of Molten Projects in the Morning 