Archive for February, 2019
Stripping the components from the back of a “5 W” COB LED gets it ready for action:
Jumpering the pads with nickel strips harvested from various NiMH and lithium cells restores the original contact pads to service:
A bit of bandsaw artistry produced a replacement for the OEM LED bracket:
The epxoy bonding the LED to the heatsink happens a few paragraphs ahead in this story, but the view justifies it. The 2 mm hole just to the right of the 3 mm SHCS aligns the heatsink to a pin in the machine’s frame, ensuring it doesn’t twist around under vibration.
The view from below (in a mirror on the machine’s bed) shows the COB LED just barely fits in the opening:
I screwed the bare heatsink into the Juki, applied double-stick tape to the COB LED, aligned LED with opening, and stuck it in place. Back in the shop, I traced around the LED to figure out what part of the heatsink needed removing, introduced it to Mr Disk Sander, and contoured it to match the LED.
Clean everything with denatured alcohol, put the heatsink on a glass plate, and clamp it to the height gauge:
Butter up the LED PCB with JB Kwik epoxy, having previously masked the contact pads (with masking tape!) to prevent oopsies:
Raise the height gauge, align LED & heatsink, lower height gauge to squish epoxy into an even layer, raise slightly to ensure the aluminum heatsink doesn’t short the nickel strips, and fast forward a few hours:
Peel off the masking tape and solder a cable in place:
The transparent doodad around the cable is a PET clamp snipped from a consumer electronics clamshell package, then punched and folded to suit. It didn’t work particularly well, so more rummaging will be required.
Foreshadowing: all this went swimmingly and looks pretty good (in a techie sort of way), but I’ve been running a nasty cold (stipulated: there being no pleasant colds). Building While Stupid is never a good idea, as the part of your brain in charge of telling you you’re about to do something catastrophically wrong is the first thing to go.
More to come …
A bipolar transistor version of the astable multivibrator with a yellow Pirhana LED required absurdly large capacitors for a reasonable blink rate and, seeing as how I need a demo circuit for Show-n-Tells, it seemed a good candidate for a faster blink. I replaced a 100 µF cap with the 22 µF electrolytic cap from the other side, installed a 2 µF cap (which, judging from the lack of polarity indicators, may be a film cap) from the Squidwrench
junk heap parts bin in its place, and hitched up the DSO150 because I brought it along:
Worked the first time and caught it in mid-blink! [grin]
The DSO150’s triggering remains a mystery, as it seems difficult to get a stable trace from a perfectly reasonable waveform. The scope didn’t trigger well on the astable’s original seconds-long pulses, perhaps due to a DC blocking cap in the triggering circuitry (whatever it may look like), but this waveform should be dead simple.
Having gained a visceral understanding of why MOSFET astables produce better battery life, this bipolar transistor design is just a milestone along the way.
Mashing the LED PCB into place didn’t entirely solve the weak beam problem, so I unscrewed the tailcap holding the switch on the other end of the body:
Unscrewing the lock ring releases the switch assembly:
I suspect the tab sticking out from the side of the switch doesn’t make / never made good contact with the aluminum tailcap body, but having gone this far there’s no reason to stop. The plastic housing around the spring-loaded brass battery contact pops off to reveal the actual switch:
The long tab on the front of the switch sits under the spring, so that’s the negative battery contact. The LED current goes through:
- battery negative to contact + spring
- switch tab + moving contact + tab
- tab to tailcap pressure fit
- tailcap threads
- front tube threads
- LED pill to PCB
- spring to battery positive
So. Many. Aluminum. Joints.
The switch body snaps apart to disgorge a remarkable number of parts:
Nothing looked out of order, so I applied a thin layer of DeoxIT Red to all the contacting parts and reassembled everything.
For the record, the switch’s internal parts have many plausible assembly sequences; the workable one goes a little something like this:
Contrary to what you (well, I) might think, the switch is off when the central contact is pushed forward, away from the side contacts.
I bent a slight angle into the tailcap contact (on the right in the picture) to make better / firmer contact with the tailcap body, cleaned all the threads with a cotton swab carrying a dab of DeoxIT, and screwed it all together.
With everything back together, the beam seems bright and steady again. We’ll see how long it lasts.
I’ve been using the J5 Tactical flashlight as a “walking light” on our walks around the neighborhood, because its bright white spot has definitely caused a few drivers to look up from their phones at the last moment and swerve away.
Of late, however, it turned on with a weak light and operated erratically. Removing the lens and unscrewing the front end revealed one mmmm potential problem:
It looks like they’re depending on the “gold” in cutaway plated-through holes to make electrical contact with the aluminum mount, then through the threads to the case. The PCB joint would work much better with consistent pressure all the way around its perimeter.
I mashed the PCB into place with a machinists vise, but, given the number of problems I’ve had with J5 flashlights (one a QC reject), they’re on my Non-Preferred Vendor list; if I’m going to get junk, I may as well pay bottom dollar.
For the record, Juki thinks this SMD LED provides enough light around the needle of Mary’s TL-2010Q sewing machine:
A detailed look at the active ingredient:
The 30 Ω resistor drops exactly 2.0 V, so the white LED runs at 67 mA.
We think it’s a glowworm, compared to the COB LED bar across the back of the arm:
Once again, maple sap rises from the ground and falls from damaged branches:
And, sometimes, a tiny sweet treat during our walks …
The final test shows the 2011-F pack may power an LED blinky, but not much else:
Although the total capacity is still about 1.3 A·h for the two best batteries, the camera says the weakest two are dead after a few photos.
For reference while resoldering, the joints at the negative terminals:
And the protection PCB on the positive end:
Unsolder the strap in the middle and the B+ positive connection on the right side to remove the cells.
If cameras used bare cells, rather than glued-shut “proprietary” packs with super-secret unique ID ROMs, they’d be easier to keep running. My Sony DSC-H5 has other problems, but NiMH AA cells are easy to find.