The Smell of Molten Projects in the Morning
Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Spotted on the way into a fast food joint:
Reading the lower meter seems particularly difficult:
Given how bollards embedded in concrete fail, they’re not providing any protection.
Did the meters get plumbed in first, with the bollards carefully fitted around them?
The butterfly bush attracted another Hummingbird Moth:
As always, those gadgets are a wonder to behold!
Photo from the Pixel 3a, zoomed all the way, and showing why digital zooming isn’t the way to get nice pictures. On the other paw, it’s the camera I always have with me.
For reasons that should be obvious by now, I volunteered to rebuild a wheelbarrow used at the Vassar Community Garden plots. It spent all its time outdoors and one of the handles eventually broke off:
I’d already removed the wheel and front strap, which were in good condition.
The new handles were undrilled, so I marked and drilled them with a nice brad-point bit to get clean holes:
The metal “barrow” had cracked around the carriage bolts holding it to the frame, so I filed a quartet of fender washers to fit the square section under the heads:
After a false start, I marked the bolt heads and washers to line them up properly while tightening the nuts on the other end:
One front strut had gone missing, so I replaced it with a mashed-and-drilled section of ski pole:
All in all, a few hours of Quality Shop Time interspersed with a few pleasant bike rides to various local stores, wherein I learned who doesn’t stock the necessary hardware.
Protip: Home Depot has the highest-entropy hardware assortment.
For the record, all the bolts have a 5/16-18 thread.
After a few days of riding, the Bafang 500C display on Mary’s bike gives the battery status:
The thermometer scale on the right shows 30% remaining battery capacity after 48.3 miles of riding, with the 11.6 A·h battery at 47.3 V.
For our type of riding, each 10% increment of battery charge delivers about 7 miles of range. Although we could probably get 70 miles between charges, recharging the battery at 20 to 30% makes more sense; the bike is in the garage, so why not?
Our typical 10 to 15 mile rides now average 12+ mph, with some level sections ticking along at 18 mph (giving me some serious exercise), which isn’t much by pro rider standards.
Computing the lithium battery charge state by measuring its voltage isn’t particularly accurate, but it’s about as good as you’re going to get.
The PCB wrapping a buck regulator around an MP1584 chip uses a tiny trimpot to set the output voltage:
The 01D resistors use the EIA-96 identifier series and are 100 kΩ.
Based on simpleminded testing, a 1 W amber LED drops about 2.5 V at 430 mA. A 1 Ω ballast resistor drops another half volt and burns a quarter of a watt, sufficient to cover some LED forward drop variation.
The trimpot is entirely too twitchy, so I replaced it with an SMD resistor:
The trimpot read 26.5 kΩ after I extracted it, but I surely nudged it a smidgen in the process.
For the record (first column is SMD topmark, second is measured resistance):
With 6.3 V @ 210 mA = 1.3 W from the bench regulator, the resistor now burns 180 mW at 425 mA and the LED burns 82% of the input power.
Letting it cook overnight settled out with the LED at 2.47 V and 440 mA = 1.09 W, with 6.3 V at 220 mA = 1.4 W from the bench supply. The LED dissipates 78% of the input power and the resistor burns 190 mW = 14%, so the regulator uses 120 mW = 8%.
I can come close to the final output voltage by plugging the new resistor value and the 8.2 kΩ resistor (on the PCB) into the MP1584 datasheet equations, but figuring the resistor to get a specific output voltage seems largely empirical.
After the rather disappointing results of the truck side marker LED light, this seems more promising:
The 1 watt amber LED is soldered to an aluminum heat spreader stuck to a scrap heatsink with thermally conductive tape. The PCB is a buck converter build around an MP1584 regulator. The lens on the left claims a 5° beam angle, which seems aspirational at best.
Not counting the heatsink, you’re looking at less than three bucks of parts; living in the future is great.
Fitting the lens over the LED produces a shatteringly bright beam, at least in the Basement Laboratory:
The lens has a conical cavity surrounding the LED lens to capture the light and redirect it to the beam forming reflector. It’s done with total internal reflection, there are no coatings, and it’s a wonder to behold: one-shot molded aspheric optics at work.
Not seating the lens firmly against the LED produces a dark spot in the middle of the beam. I soldered the leads directly to the LED and cut out the sides of the black lens holder, as soldering them to the convenient side pads would prevent the lens from seating properly.
The LED drops about 2.5 V at 430 mA (1.08 W). The bench supply delivered 6.3 V at 190 mA (1.2 W) to simulate the headlight output of the Bafang motor controller.
The headlight output is good for 6-ish V and 3 W = 500-ish mA, so burning half the power in a simple dropping resistor or linear current regulator is a Bad Idea™. You can get constant current LED drivers, but apparently not with 6 V input and 1 W output, so stepping the voltage down makes more sense. You’d want at least a little ballast resistor in there to soak up small forward drop changes with temperature variations.
The regulator can handle up to 28 V input and the tiny trimpot must cover nearly that range of output voltages, so the 2.5 V output jams it near the minimum end of its rotation (which is, of course, backwards). This calls for a fixed resistor to eliminate the effects of vibration on a trimpot at 10% of its range.
Mary found a rusted Fiskars bypass pruner in the trash pile near her Vassar Farms plot and brought it home for proper disposal. The nuts and screws responded to an overnight penetrating oil treatment and it came apart easily:
The movable jaw may have once sported a PTFE coating, but it’s likely just a different steel alloy.
After scrubbing the pieces with an abrasive pad, a little diamond filing, and (at the insistence of the Squidwrench chorus) some Dremel wire-wheel action, it looks almost new:
The blades sport a few nicks from their previous life, but work well enough.
The Smell of Molten Projects in the Morning 