Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Being that type of guy, I noted each date when my Sonicare toothbrush needs recharging, at least after the battery had declined to about a week between charges, specifically so I could produce this graph:
Sonicare Runtime
The peaks include trips where I didn’t use the toothbrush and I’ve certainly blundered a few dates, but you can eyeball a trendline: those cells are kaput!
In round numbers, I bought the thing in early 2010, so the cells lasted maybe 2-½ years. I routinely run the toothbrush until the blinky light indicates that it needs charging, then fill it up overnight, to avoid having the cells fail like the ones in the beard trimmer.
Somehow the notion of discarding the whole toothbrush seems wrong, even though the instruction manual describes how to remove the battery for recycling before you junk the carcass. Talk about planned obsolescence!
Alas, urethane glue didn’t hold the eye marbles in the garden dragonfly ornament for very long. Although the cured glue had a wonderfully smooth surface where it contacted the balls and it had plenty of contact area, that wasn’t enough.
This time, I used acrylic caulk that should stay gummy enough to maintain a good grip:
There ought to be a survey marker pin at the front corner of the lot where it’d come in handy for locating the edge of the yet-to-be-contracted driveway paving, but if it’s there it’s been pushed below ground level. So I mooched a homebrew metal detector based on the Elenco K-26 PCB…
K-26 Metal Detector PCB
The kit included 45 feet of 22 AWG enamel wire that should have become a 5 inch diameter coil with 30 turns, but the as-built detector had a coil wrapped around a 1 foot diameter cardboard form. The coil inductance sets the oscillation frequency, which turned out to be around 300 kHz: far below the nominal 1000 kHz. So I wound 40 turns of 22 AWG magnet wire around an old CD-ROM spindle case (which is, quite coincidentally, just over 5 inches in diameter), and taped it atop the cardboard form.
The datasheet recommends a nonmetallic handle, so I swapped in a plastic umbrella support for the original metal mop (?) handle.
Rewound homebrew metal detector
The K-26 schematic looks like a common-base Colpitts oscillator, with only the most utterly absolutely vital essential components:
K-26 Schematic
In round numbers, the oscillation frequency varies inversely with the number of turns:
F = 1/(2π√(LC)) (for a simple tank)
L = stuff × N2 (stuff = various constants & sizes)
F = stuff / N
The rewound coil oscillated at 350 kHz, so I spilled off a few turns at a time to produce these results and a tangle of wire on the floor:
L – µH
Freq – kHz
330
350
186
535
107
711
65
840
42
1140
For the record, the coil in the photo corresponds to the last line and has 12 turns.
Contrary to what the instructions imply, trimpot P1 does not adjust the oscillation frequency. It tweaks the transistor bias for best oscillation, so it’s more of an amplitude control than anything else. I adjusted P1 while watching an oscilloscope connected across the negative battery terminal and the emitter of Q1, but you could probably use a small sniffer loop to good effect.
It draws about 2 mA, so the battery should last quite a while; labeling the switch positions should help a lot.
The oscillator produces an unmodulated carrier, so I tuned a Kenwood TH-F6A HT in LSB mode for maximum squeal. Any variation in L changes the carrier frequency and thus the pitch of the demodulated audio; an earbud just barely in one ear makes this almost tolerable.
As you should expect from the picture, that metal detector lashup is mightily microphonic, to the extent that touching a blade of grass wobbles the audio pitch and bumping the cardboard plate against an object can detune the whole affair. A bit more attention to rigid coil mounting would certainly help, but this isn’t the most stable of designs to begin with and I doubt anything will help very much at all.
The coil can detect a chunk of rebar sticking out of the ground at a range of maybe half a foot, but it’s not clear how well it will cope with buried treasures (like, oh, let’s say a survey marker pin). In any event, I must mow the grass down there before going prospecting.
Now that I carry a spare tube on the bike to avoid on-the-road patching, a tangle of tubes has been accumulating in the Basement Laboratory. A protracted patching session shows why you can never have too many clamps:
Repaired bike tubes with clamps
Yes, I know they’re supposed to be ready to ride immediately after slapping the patch in place. Clamping the patch overnight won’t hurt and might actually help eliminate slow leaks, soooo… after this, they’re rolled up and ready for another season of punctures.
Repairing tubes goes much easier in the shop than by the side of the road, though. For what it’s worth, those silicone tape pads didn’t help much at all; the tube still eroded at the liner. Grumble…
The relatively low capacity at 100 mA (black) shows that the boost converter isn’t particularly efficient; the discharge time is long enough that power loss in the booster outweighs the cell’s higher capacity at lower loads.
Surprisingly, the voltage drops to 4.5 V at 500 mA, which is what you should get from a typical USB port. If the device you’re charging expects the nominal 5 V at 500 mA, it will be sorely disappointed. Admittedly, that’s only 10% low, but …
The booster produces only 4.0 V at 1 A, with odd bumps as the cell discharges. Huh?
I know for a fact that my 1.8 A @ 5.0 V Kindle Fire doesn’t even notice it’s plugged into the Powermonkey. The voltage is probably too low to trigger the “External Power, Ahoy!” signal.
Bottom line: it’s not clear this thing actually works for contemporary devices. Maybe newer Powermonkey products behave better?
Here’s a great example of painting yourself into a corner…
Back in the day, I made a voice-only interface that adapted a helmet-mounted electret mic and earbud to an ICOM IC-Z1A HT. A pair of those let us talk companionably as we rode along.
Along comes our daughter, with her shiny-new Technician amateur radio license. I took an early version of the Z1A interface board, force-fitted it into an early version of the machined case that lacked a top, acquired an ICOM W32A HT and another TT3+, did some tweakage, and defined the result as Good Enough. Time passes, she’s promoted to Larval Engineer, goes off to college, and leaves the bike behind (a faired Tour Easy is ill-suited to being left out in the rain and is not a dorm-room-friendly bike).
Knowing that the Z1A on my bike is failing, I get a Wouxun KG-UV3D HT and modify the Z1A interface to match. Then I build an interface PCB for the KG-UV3D, conjure up a nice case (which is why I bought a 3D printer), chop the TT3+ out of the W32A lashup, put everything together, and it’s all good.
Here’s the carcass of the W32A interface in its half-case:
W32A PCB in case
Whereupon our Larval Engineer returns from college and once again needs a radio for her bike. At that point:
The W32A interface now lacks its TT3+.
The W32A PCB doesn’t fit in the Z1A case
The Z1A interface that would fit the W32A radio has the KG-UV3D modifications.
The Z1A radio has failed completely; it no longer even turns on.
Some alternatives:
Get another KG-UV3D, build another interface PCB + case, make it work
Transplant the TT3+ back to the W32A interface
Undo the KG-UV3D mods from the Z1A interface, put it on the W32A
Given that she’s going to vanish in another three months, tops, Choice 1 is out. Although the transplant in Choice 2 seems straightforward, it requires tedious soldering and produces an interface in a partial case.
So Choice 3 it is…
The Z1A board with the KG-UV3D modifications started out like this:
Z1A PCB modified for Wouxun KG-UV3D
Un-modified again and back in its machined case:
Z1A board minus mods – milled case
Buttoned up and ready to roll:
Z1A board on W32A – ferrite core
I put a clamp-on ferrite tumor around the GPS receiver cable to keep RF out of the TT3+, which seems quite sensitive to RFI; the poor thing locked up quite dependably on the bench with 5 W into a long rubber duck antenna, but not into a dummy load. The mobile antenna sits relatively far from the radio on the bike, but I think the TT3+ had problems in the early KG-UV3D lashup.
The TT3 audio level will probably require adjustment, as I’d cranked it up for the KG-UV3D, but that will require some on-the-air testing. Ditto for mic level.
When I get a KG-UV3D for Mary’s bike, I’ll buy two radios and build two interfaces, so as to finally have a working radio + interface on the shelf.
I’m mildly tempted by the new Yaesu VX-8GR, but that’s over $350 for a radio that also requires a new interface board design, a new case design, a new set of adapters, and other odds&ends. Not to mention that the radio’s built-in GPS antenna would live at the bottom of the seat frame beside the wheel and below my shoulder. I suppose I could conjure up an entirely new radio mount, but … the deterrents seem overwhelming.
Various versions of the schematics & PCB layouts for all those boards, plus solid models for the 3D printed case, are scattered here & there on other posts.
Quite some time ago I got a Powermonkey Explorer set (the one with a solar panel charger) at a substantial closeout discount. After the marketspeak dissipates, it’s a single lithium-ion cell with a boost regulator and USB charger inside a screaming yellow case (the new ones seem more subdued) that’s somewhat water resistant, along with a kit of adapters for various widgets & phones. It stopped charging from the solar panel or a USB port, which suggested that I had little to lose by cracking it open.
It’s an odd shape, but grabbing it across the equator and applying gentle pressure cracked one side:
Cracking Powermonkey case
Wedging a screwdriver in the opening and twisting a bit freed the other side:
Enlarging Powermonkey case crack
Then it was just a matter of pulling gently to expose the cell & circuitry within:
Powermonkey interior
That seems to be a standard 18650, presumably similar to that 2.2 A·h cell.
I didn’t find anything obviously wrong, so I buttoned it up with screaming yellow silicone tape, put it on its wall-wart charger for a bit, and now it’s all good again: a shining example of a laying-on-of-hands repair.
The single button has much more travel than it should, so I think the internal foam supports have lost their springiness.
The Smell of Molten Projects in the Morning 