Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The plastic-ball-in-plastic-socket joint found in bicycle mirrors seems to fail after a year or two of constant use. These are some doodles & thoughts about building a small, robust, adjustable joint.
A bike mirror needs two ball joints:
at the helmet mount to put the mirror in the proper spot
at the mirror to align the image
A flexy boom can replace the helmet joint, although rotation around X (pitch) is still handy.
A flexy mirror mount can replace the mirror joint, but it must also be compact.
Without heroic measures, the range of travel for a ball joint isn’t all that much.
How to make a ball? Anneal & drill a standard ball bearing for a wire shaft? Solder onto chrome steel? CNC mill the end of a bar in a rotary table?
How to make a socket? Some of that low-temperature themoplastic might be useful. Mold it around the ball, slit radially, and squash it in a circ clamp?
How to adjust? Circumferential clamp around the socket or pull the whole socket into a wedge? Radial cuts through the socket to allow compression or depend on plastic/elastic deformation?
How much friction? You want it stiff enough to hold position in a strong wind and easy enough to reposition. You definitely don’t want grub screws or fiddly knobs!
The doodles are all far too complex, some are absurd, one can’t be built (at least by me), and I’ll probably end up using some bendy wire anyway.
Something of this may be useful in another project … and now I can throw out that scrap of paper.
As described there, I made a fixture and a small plate to hold 2.5 mm and 3.5 mm plugs in the proper alignment for the mic & speaker jacks on our ICOM IC-Z1A HTs. Knowing I was going to rebuild the interface boxes, I made several spare plates and tucked them into a small bag against future need.
Jack Plates – Oblique
Time passes.
Come to find out that the new gratuitously gold-plated 2.5 mm plugs in my stash have a slightly thicker front plate that doesn’t quite fit into the recess I milled in the plates for the old nickel-plated plugs. So I set up a little nest in on the Sherline’s table, snuggled each plate into the corner, and poked a 9/32-inch end mill 1 mm down into the plate. The net change was a 0.5 mm deeper recess. Sheesh.
Milling the plug plate recess
I’d originally create the recess with helical milling, but I recently uncovered a stash of shiny-new end mills in a box: 9/32 is 7.31 mm, just about exactly what you want for a 7-mm dia plug front plate surrounded by a blob of fast-curing epoxy.
Plugs epoxied into plate
This epoxy just holds the plugs in the right position for wiring and initial testing. After the cable checks out, I’ll smoosh a blob of epoxy putty around the whole thing as before.
The circuit board is 30-mil, double-sided, half-ounce (I think) copper on glass-fiber stock, direct-etched by rubbing ferric chloride solution onto it with a sponge.
The top copper image (on the left) is reversed so it comes out correctly when you’re doing toner-transfer etching.
I didn’t bother with a silkscreen, because I don’t have a soldermask and there’s no room for text around the parts anyway.
The four vias at the corners mark the edge of the board. Trim it with tinsnips (or a shear if you have one), then introduce it to Mr Belt Sander until the edges pass directly through the middle of those via holes. Round the corners a bit so they fit into the case recess atop the mounting shoulder.
Put Z-wires in the small round vias (the ones that don’t have any other traces) to connect the top and bottom ground planes.
Put Z-wires in the other round vias to connect a top-side signal to the corresponding bottom-side trace.
There are three jumper wires across the bottom; with only two layers I don’t get all bothered about embedding the last few. Those vias are square.
I don’t have any way to do plated-through holes, so solder the wires to both sides of any vias with traces on both planes. I admit I missed two of them on the TT3 ribbon cable.
The big empty space around the positive power terminal prevents the ring-lug connector from shorting to the ground plane. Now that I think of it, there’s no need for an empty space on the bottom copper, but it doesn’t do any harm.
This board drives the helmet mic & earbud, combines the TinyTrak3+ AFSK audio with the mic audio, and interfaces with the radio’s mic & speaker jacks.
GPS + Audio circuit board
The schematic (click for more dots):
GPS + Voice HT Interface schematic
The ICOM IC-Z1A provides a 3.5 V power supply (on the ring terminal of the mic jack) that normally drives an electret mic. I use it to turn on a MOSFET relay that powers all the circuitry directly from the external battery pack. The relay has about 1 Ω of resistance, so there’s not much voltage drop. Note that the radio’s power does not go through the relay: it connects directly to the external battery.
An earlier version used an optocoupler to drive a 2N2907 PNP transistor for power switching. That worked fine and might actually be better; I think the MOSFET relay needs slightly more drive current than the HT’s 3.5 V supply can provide. More on that later if the problems continue.
The TinyTrak3 includes a 5 V regulator that I wired through the normally unused pin 9 of the DB-9 connector (no connector, just a ribbon cable). It powers the PTT button, analog switch, and the PTT optocoupler.
The MAX4467 handles the electret mic, with power from a separate 5 V shunt regulator built around an LM336. That keeps much of the TT3’s digital noise out of the audio. You can use a MAX4468 if the voltage gain required for your electret mic capsule is greater than Av=5; the ’67 is unity-gain stable.
A MAX4544 analog switch (basically, a low-power MOSFET relay) selects either voice or AFSK data. I originally tried adding the two with an op-amp, but there’s just too much noise from the TT3. The external PTT selects audio data; the rest of the time the radio gets the TT3.
The HT’s mic input is galvanically isolated from the rest of the circuit board. That eliminates ground loops, circulating RF, and all manner of hassle. Bulky, awkward, expensive, and highly worthwhile.
An optocoupler isolates the TT3 PTT-out signal from the HT’s audio input, while switching the 33 kΩ resistor that activates the HT PTT. R18 bypasses any leakage current from the TT3’s driver transistor around the coupler’s LED; the PTT current to the HT is so small that the leakage on a hot day can tease it.
A small 1:1 audio transformer couples the voice + data into the HT’s mic input jack. The 1 μF caps are certainly overkill, but they’re small and work well.
The HT’s external speaker goes into a simple L attenuator that reduces the volume. The HT expects an 8 Ω speaker, but most of the earbuds these days are 30 Ω and way loud; the volume control doesn’t have much resolution when there’s only two or three clicks between inaudible and ouch.
All the external inputs have a 100 pF bypass cap and a 100 Ω series resistor to cut down on RF and tamp down static discharges. Might be overkill, but the previous units withstood years of abuse with that sort of circuitry and I’ll stand by it.
Required tweakage for your HT’s preferences:
R9: MAX4467 gain gets the electret capsule output up to whatever your HT expects.
R15/R16: Earbud attenuator cuts the HT’s speaker output down to something reasonable for your ear
R14: PTT resistor must suit your radio
R19: TT3 output may be too hot for your HT audio, even with R6 on the TT3 turned way down.
All the wires go to top-layer solder pads, rather than physical connectors. I didn’t have any “front panel” space for connectors, anyway, so that’s as good as it gets.
I’ll eventually gather all the files into one lump and put ’em up here.
The boards fit in the two halves of the enclosure, which is held together by four 7/8-inch 2-56 machine screws. The blind holes in the lower (right) half are tapped for the screws. The clearance holes in the upper (left) half are a bit too close to the interior; if the setup isn’t perfect, they break through.
The right half slides into the HT’s battery pack grooves. The two tin plates match up with the HT’s power input contact springs.
Interface – top and bottom surfaces
The oval mark around the four LEDs is actually a 1 mm deep recess in the cover; the LEDs are the tallest things on the board and I sort of ran out of room. The GPS connector is essentially flush against the back of the HT, so the board can’t get any lower. Even though the case halves are milled from a hulking 3/4-inch plastic plate, the top surface is only 1 mm thick above the LEDs, so the board can’t get any higher.
The interior view:
Interface box – interior
The DB-9 serial connector mounting screws hold the TinyTrak3 board in place. The GPS receiver and PC serial port (used for configuration) plug into that connector.
The four external cables connected to the circuit board:
power from external battery pack
helmet mic + earbud
PTT switch
HT speaker + mic + mic power
A closeup of the audio PCB in its natural habitat:
GPS + Audio circuit board
The two nuts on the right fit on 4-40 brass screws that I converted into studs under those tin battery pack strips, about which more later. The nuts hold the circuit board in place atop a shoulder around the interior of the compartment.
The OEM battery packs have nice tabs that engage the HT’s clever pushbutton latching mechanism. I spent a lot of time staring at them: they’re easy to do in an injection mold and impossible to machine at my skill level. So I punted: two strips of tape hold the enclosure in place on the HT. Works fine.
You’ve seen bits & pieces of this in the previous weeks and months: now it’s up and running!
Admittedly, this is brassboard hardware; I must now build three final versions for our bikes incorporating all the tweaks & adjustments. But it’s time to write this stuff down so I can find it again … and perhaps you can use some chunks, too.
I don’t have an instruction manual to go along with this, nor is there a parts kit available. You’ll certainly want to modify everything for your own purposes; the circuit board and case certainly won’t fit whatever HT you’re using!
Over the next several days, I’ll be describing & documenting the tricky parts… in no particular order, because I’m not going to sort my notes & photos ahead of time.
This is another step along the way to getting our daughter’s radio firmly mounted to her Tour Easy, not tucked into one of the panniers. The general idea is to use a water bottle holder for the radio, with a seat wedge pack from an upright bike cushioning the radio. The secret ingredient is a circumferential clamp that mounts the holder to the lower rail of the bike’s seat frame.
This clamp is basically the same as the ones on our bikes, but I doodled up a sketch with some illegible dimensions that almost matches the actual clamp; we may both find it useful the next time.
Clamp layout sketch
Machining the clamp is straightforward: bandsaw a block of about the right size, square it up in the mill, helix-mill the clamp hole …
Helix-milling the clamp hole
Drill the clearance and tapping holes for the screw, bandsaw it in half, clean up the cut edges …
Finished clamp parts
Obviously, I didn’t put those nice bevels on the front side.
Both previous water bottle holders required a spreader plate between the clamp screws and the holder’s screws, but this time the holder had a nice aluminum plate all by itself. It just fit on the Sherline and a bit of manual CNC center-drilled the curved plate and poked a jobber-length drill through the holes …
Drilling holder for clamp screws
And then it fit perfectly on the bike …
Mounted holder
A side view …
Mounted holder – side view
Now, to find a wedge pack big enough for the HT and small enough to fit in the holder!
The Smell of Molten Projects in the Morning 