Archive for category Electronics Workbench
A new floor lamp arrived with the usual dark-gray-on-black annotations on an absolutely non-tactile pair of capacitive controls. For a device intended for use in a dim room, this makes little sense, unless you’re both trendy and concerned about manufacturing costs.
A strip of 1/4 inch Kapton tape added just enough tactility to find the damn buttons without looking at the lamp head:
The pole’s non-adjustable length put the lamp head well above eye level, so I removed one pole segment. This required cutting the 12 V zipcord and crimping a pair of connectors:
I briefly considered conjuring a skinny connector, but came to my senses: there’s plenty of zipcord if I must chop out the connectors, particularly seeing as how shortening the pole added a foot.
The setscrew at the bottom of the gooseneck crunched the zipcord against the metal shell. A polypropylene snippet made me feel better, even if it makes no difference:
After all that, It Just Worked™:
Thinking of strapping a big external cell next to my Sony HDR-AS30V helmet camera, I took a look inside a defunct NP-BX1 lithium batteries:
Peeling off the wrapper holding the end caps in place reveals some ID on the cell:
The bottom end cap is just a plastic bumper held on with glue and tape:
The top end cap has keying indents, identifies the terminals, and falls off without the wrapper:
The C and – terminals use the same PCB pad.
The black plastic around the PCB pulls just far enough away from the cell to expose the tabs welded to the terminals:
Snip ’em and it’s done:
As with all lithium cells, the can is + and the isolated tab is -.
Given that I have a stack of tabbed 18650 cells, I’m thinking of building a cell into a structure snapping into the AS30V’s helmet mount, along with a charge controller PCB. I normally remove the camera from the helmet and bring it inside and, since I must open the back to extract the MicroSD card, plugging a USB cable into the charger isn’t much of an imposition.
More pondering is in order.
Spotted in a museum:
It’s been quite a while since BIOS boot sequences started with the floppy drive. Combined with a CMOS backup battery failure, I’d say this poor PC has been chugging along for two decades.
On another floor:
Isolating a Windows kiosk from the Interwebs is an excellent design principle, but Windows Update really wants to phone home. The kiosk’s presentation ran Adobe Flash 10, so it’s been confined for maybe a decade.
Looks like it’s time for another fundraising drive to replace the PCs with Raspberry Pi controllers. The real expense, of course, goes into rebuilding the presentations using whatever tech stack is trendy these days.
Following a linkie I can no longer find led me to retrieve the Tektronix Circuit Computer in my Box o’ Slide Rules:
I’m pretty sure it came from Mad Phil’s collection. One can line up the discolored parts of the decks under their cutout windows to restore it to its previous alignment; most likely it sat at the end of a row of books (remember books?) on his reference shelf.
The reverse side lists the equations it can solve, plus pictorial help for the puzzled:
Some searching reveals the original version had three aluminum disks, shaped and milled and photo-printed, with a honkin’ hex nut holding the cursor in place. The one I have seems like laser-printed card stock between plastic laminating film; they don’t make ’em like that any more, either.
TEK PN 003-023 (the paper edition) runs about thirty bucks (modulo the occasional outlier) on eBay, so we’re not dealing in priceless antiquity here. The manual is readily available as a PDF, with photos in the back.
Some doodling produced key measurements:
All the dimensions are hard inches, of course.
Each log decade spans 18°, with the Inductive Frequency scale at 36° for the square root required to calculate circuit resonance.
Generating the log scales requires handling all possible combinations of:
- Scales increase clockwise
- Scales increase counterclockwise
- Ticks point outward
- Ticks point inward
- Text reads from center
- Text reads from rim
I used the 1×100 tick on the outer scale of each deck as the 0° reference for the other scales on that deck. The 0° tick appears at the far right of plots & engravings & suchlike.
The L/R Time Constant (tau = τ) pointer on the top deck and the corresponding τL scale on the bottom deck has (what seems like) an arbitrary -150° offset from the 0° reference.
The Inductive Frequency scale has an offset of 2π, the log of which is 0.79818 = 14.37°.
The risetime calculations have a factor of 2.197, offsetting those pointers from their corresponding τ pointer by 0.342 = log(2.197) = 6.15°.
A fair bit of effort produced a GCMC program creating a full-size check plot of the bottom deck on the MPCNC:
By the conservation of perversity, the image is rotated 90° to put the 1 H tick straight up.
The 3018 can’t handle a 7.75 inch = 196 mm disk, but a CD-size (120 mm OD) engraving came out OK on white plastic filled with black crayon:
The millimeter scale over on the right shows the letters stand a bit under 1 mm tall. And, yes, the middle scale should read upside-down.
Properly filling the engraved lines remains an ongoing experiment. More downforce on the diamond or more passes through the G-Code should produce deeper trenches, perhaps with correspondingly higher ridges along the sides. Sanding & polishing the plastic without removing the ink seems tedious.
The Great Dragorn of Kismet observes I have a gift for picking projects at the cutting edge of consumer demand.
More doodles while figuring the GCMC code produced a summary of the scale offsets:
Musings on the parameters of each scale:
How to draw decades of tick marks:
It turned out easier to build vectors of tick mark values and their corresponding lengths, with another list of ticks to be labeled, than to figure out how to automate those values.
More on all this to come …
Recharge and test to get the blue lines, with the red lines from the DOT-01 batteries:
The double blue line came from a second recharge of that battery, just to see if more electrons would help. Nope, it’s still dead.
The Wasabi battery with the highest capacity also has the weirdly rippled voltage trace and, when I extracted it from the test holder, came out disturbingly warm and all swoll up. This is A Bad Sign™, so it spent the next few hours chillin’ on the patio and now resides in the recycle box.
A Dell soundbar under the landscape monitor suffices for my simple audio needs, and, when the Dell U2711 went toes-up, I conjured a 12 V wart from the heap. A recent cleanup made a smaller wart available, but required mating two coaxial plugs:
A snippet of brass tube suffices for the center pin. The outer shell is a larger brass tube, slit lengthwise, trimmed to fit the plug circumference and rolled around a smaller drill bit to make it springy in the right direction.
A wrap of silicone tape and it’s all good:
Ugly, but good.
One of the wireless numeric keypads I’ve been using with the streaming radio players developed some intermittent key switch failures resisting all the usual blandishments. Eventually it hard-failed, but I was unwilling to scrap the tediously printed keycap labels:
Hard to believe, but I’ve been using the white keypad for plain old numeric entry with the keypad-less Kinesis Freestyle 2 keyboard.
I swapped the Frankenpad + receiver to the least-conspicuous streamer and, someday, I’ll update all the labels on all the keypads to match the current streams. Until then, the white keycaps shall remain in the same bag as the defunct black keypad, tucked into the Big Box o’ USB mice & suchlike.