Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Eight minutes later, we’re turning onto the Dutchess County Rail Trail:
Losing the Battery Bag – flight – 2019-02-25
And then it’s gone:
Losing the Battery Bag – gone – 2019-02-25
Mary drove past there on her way to a distant meeting, but the little red bag was not to be found anywhere. Maybe it’ll reappear on a fence post or taped to the bulletin board; I’ve tried to return things I’ve found that way.
I expect somebody got a nice present and, if naught else, it’s good to drop happiness into the world.
There’s another reader and a quartet of batteries on their way.
Our CVS blood pressure meter (a relabeled Microlife unit) ran its pump for a few seconds this morning, gave up, and spat out Err 3, which translates into “Inflation of the cuff takes too long”. Not surprising, as the motor wasn’t running.
The AA alkaline cell quartet has plenty of mojo and no corrosion, but the motor doesn’t even turn over. The display is fine and the pressure release valve clicks, so it’s not completely dead.
This unit is sufficiently old to have the compelling advantage of transferring data through a USB (mini-B) connection, rather than a Bluetooth link through some sketchy Internet cloudy Android app, so it’s worth at least a look inside. Four screws and some internal snaps along the sides hold the case together; it’s a surprisingly easy teardown.
The business side of the PCB looks good:
CVS Blood Pressure Monitor – PCB
The various wires and solder joints for the “high current” parts look OK, although the wires likely don’t go all the way through the PCB:
CVS Blood Pressure Monitor – PCB detail
Q4 and Q5 look like they switch the compressor pump motor and pressure-release valve. D3 and D4 should tamp down the inductive energy, but they look like they’re in series with the outputs. Yes, the Valve wires are both black.
The motor has a foam vibration isolation wrap, which is a nice touch. Although you can’t see them well, all its wires & solder joints look like they’re in good shape:
CVS Blood Pressure Monitor – pump
The hose sticking out toward you plugs into the black right-angle fitting in the lower right corner of the picture. It’d help to have smaller fingers than mine, but I managed to get the hose off and on the fitting with only minor muttering.
Seeing nothing obviously wrong, I installed the same batteries, poked the switch to start a measurement, and the motor ran fine. Of course, the measurement failed because the cuff & pressure sensor weren’t connected.
Connect the hose, plug in the cuff & wrap it around my arm, poke the button, and everything works fine.
Reassemble everything and it still works fine.
I still think there’s a bad wire or solder joint in there somewhere, so this delightful “repair” can’t possibly last very long …
Mitchell 8.6 – Longitude computations of occultations 1872-1875
Here’s what “calculations” looked like in 1872:
Mitchell 8.6 p9 – Occultation of 1253 BAC at 11 hrs – calculation
Yeah, grinding out trigonometry by hand using seven-place logarithms:
Mitchell 8.6 p9 – Occultation of 1253 BAC at 11 hrs – calculation detail 1
Not just by hand, but by hand with pen and ink:
Mitchell 8.6 p9 – Occultation of 1253 BAC at 11 hrs – calculation detail 2
Although you’ll find an occasional ink blot, she was probably using a fountain pen, rather than a dip pen, and made very few mistakes along the way. She often recorded direct instrument observations in pencil.
The next time you start pissing & moaning about how hard solid modeling is, suck it up.
Bonus: a Ginger Snap recipe suggesting it wasn’t all toil & trouble in the observatory:
Mitchell 7.5 – Ginger Snap recipe
The mystery ingredient is saleratus, “aerated salt”, now known as baking soda; they used potassium bicarbonate before today’s sodium bicarbonate.
The quadrature detector, the black block on the left, is oriented with its lens (and, thus, the actual detectors) pointed away from the IR emitter. I thought it might be an assembly screwup, but it’s actually worse: the PCB layout is wrong.
A note from Tristan in NZ explains the situation:
So I have a later model than yours. It has a 2nd PCB chunk between where the legs normally would be. Just a floating piece with two holes for the legs, holding the legs from the board […] to the main board.It is also pointing the correct way (with the lens towards the three leg emitter).
Kensington scroll wheel revision2
The new quad detector has only three pins and no convex lens, but the active area now faces the emitter across the gap.
Because the interposer PCB occupies the space previously devoted to the emitter & detector leads, Kensington apparently soldered the new parts directly to the top surface without any clearance:
It’s like they failed to put through-vias to the rear or didn’t route them to the bottom another way, hence the solder is under the component
Tristan managed to wreck the detector while attempting to re-solder the intermittent joints, a situation I’m painfully familiar with. He replaced it with a quad detector harvested from a mid-90s optical mouse and it’s back in operation.
So I think the correct “fix” for the old-style PCBs (without the new interposer) is to unsolder the detector, rotate it so the lens faces the emitter, then somehow rewire the pins to the original pads. This won’t be easy and definitely won’t be pretty, but as long as it’s pointed in the right general direction it should work:
mine works off axis quite a bit
Should either of my Expert Mouse trackballs fail, now I know what to do
Many thanks to Tristan for reporting his findings!
I’ve always wondered what’s inside a metal-case vacuum tube:
Dual rectifier tube 5T4 – metal case opened
The cutter last saw action on the EMT used in the MPCNC, so it’s intended for use on steel tubes. I thought about parting the case off in the lathe, but a tubing cutter sufficed for a first attempt, even if it couldn’t cut quite as close to the flange as I wanted.
A 5T4 tube is a full-wave rectifier with two sections:
Dual rectifier tube 5T4 – upright
Unsurprisingly, the guts resemble those of glass-envelope rectifier tubes in my collection, like this 5U4GB:
5U4GB Full-wave vacuum rectifier – cyan red phase
The metal case would be far more rugged than a glass bottle and, perhaps, the flange locked the tube into its socket against vibration.
The filaments surely weren’t thoriated, so it’s all good …
In those 29 calendar months (maybe 20 riding months) I’ve ridden 4500-ish miles at perhaps 12 mph, so call it 375 hr = 22.5 k min. The camera fills a 4 GB file every 22.75 min, so it’s recorded 1000 files = 4 TB, which is 62× its capacity. This is better than the defunct Sandisk Extreme Pro card (3 TB & 50×) and much much better than the Sony cards (1 TB & 15×), although I have caught the camera in RCVR mode maybe twice, which means the card or camera occasionally coughs and reformats itself.
The SJCam M20 rear camera also uses a Sandisk 32 GB high-endurance card and has worked fine since early 2018. An external battery eliminated all the hassle of its feeble internal batteries, although the one that’s been in there has faded to the point of just barely keeping the clock ticking over during winter weeks without rides:
SJCAM M20 Mount – Tour Easy side view
All in all, paying the premium for video-rated MicroSD cards has been worthwhile!
The GCMCtypeset() function converts UTF-8 text into a vector list, with Hershey vector fonts sufficing for most CNC projects. The fonts date back to the late 1960s and lack niceties such as superscripts, so the Homage Tektronix Circuit Computer scale legends have a simpler powers-of-ten notation:
Tek CC – Pilot V5 – plain paper – red blue
Techies understand upward-pointing carets, but … ick.
After thinking it over, poking around in the GCMC source code, and sketching alternatives, I ruled out:
Adding superscript glyphs to the font tables
Writing a text parser with various formatting commands
Doing anything smart
Because I don’t need very many superscripts, a trivial approach seemed feasible. Start by defining the size & position of the superscript characters:
SuperScale = 0.75; // superscript text size ratio
SuperOffset = [0mm,0.75 * LegendTextSize.y]; // ... baseline offset
Half-size characters came out barely readable with 0.5 mm Pilot pens:
Tek CC – Superscript test – 0.5x
They’re legible and might be OK with a diamond drag point.
They work better at 3/4 scale:
Tek CC – Superscript test – 0.75x
Because superscripts only occur at the end of the scale legends, a truly nasty hack suffices:
function ArcLegendSuper(Text,Super,Radius,Angle,Orient) {
local tp = scale(typeset(Text,TextFont),LegendTextSize);
tp += scale(typeset(Super,TextFont),LegendTextSize * SuperScale) + SuperOffset + [tp[-1].x,0mm];
local tpa = ArcText(tp,[0mm,0mm],Radius,Angle,TEXT_CENTERED,Orient);
feedrate(TextSpeed);
engrave(tpa,TravelZ,EngraveZ);
}
The SuperScale constant shrinks the superscript vectorlist, SuperOffset shifts it upward, and adding [tp[-1].x,0mm] glues it to the end of the normal-size vectorlist.
Yup, that nasty.
Creating the legends goes about like you’d expect:
The Smell of Molten Projects in the Morning 