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.
Things around the home & hearth
A giant envelope containing one of those “political surveys” that’s actually a thinly disguised fundraiser arrived, with this confidence-inspiring ID in the upper-right corner:
The questions were all examples of false dichotomies.
A pox on their backsides, sez I.
Got a call from a friend who was having trouble getting BitDefender to accept its new license key, so I drove over; she’s at the top of a killer hill and I’d already biked my two dozen miles for the day. Solving that problem was straightforward, if you happen to know that they use “authorization” and “license” as synonyms and that you access the key entry dialog by clicking on a text field that doesn’t look at all clickable.
I should have declared victory and returned to the Basement Laboratory, but, no, I had to be a nice guy.
BitDefender kvetched that it had been 777 days since its last scan, so I set up some regularly scheduled scans and automagic updates for everything in sight; we agreed she’d just let the thing run overnight on Mondays to get all that done.
BitDefender also suggested a handful of critical Windows XP updates, plus the usual Adobe Flash and Reader updates, plus some nonsense about Windows Live Messenger that seemed to require downloading and installing a metric shitload of Microsoft Bloatware. Rather than leave all that for next Monday’s unattended update, I unleashed the critical ones, did the Flash and Reader updates, and stuffed the Messenger update back under the rug.
Then AOL recommended an urgent update to AOL Desktop 9.7. She has a couple of AOL email addresses, mostly for historic reasons, and I asked if she ever used the AOL Desktop. She wasn’t sure, so I lit up the installed AOL Desktop 9.6: “Oh, that’s how I get all my email!” OK, so we’ll update that, too.
After all the thrashing was done, the system rebooted and presented us with the single most unhelpful error message I’ve ever seen:
No, you chowderheads, that is not OK…
Searching on the obvious terms indicated this had something to do with Internet Explorer 8 (remember IE 8?) and produced a number of irrelevant suggestions. The least awful seemed to involve running the Microsoft System File Checker utility:
sfc /scannow
Which I did.
It ran for the better part of an hour, then suggested a reboot. During the shutdown, it replaced 29 files at an average of about 5 minutes per file.
After which, Windows restarted and displayed exactly the same error message. Actually, a series of them; various programs couldn’t locate a fairly wide selection of ordinals in several DLLs.
OK. I give up.
We located a tech who does this sort of thing for a living. I’ve offered to split the cost of getting the box up and running again, with the understanding that it may be easier to start with a fresh off-lease Dell box running Windows 7 than to exhume an aging Windows XP installation.
I stopped caring about Windows toward the end of the last millennium and now keep a Token Windows Box only for hardware like the HOBOWare dataloggers and software like TurboTax.
Other than that, well…
I. Don’t. Care.
A bit of rummaging in the Big Box o’ Weatherstripping produced the stub end of a spool bearing 1/4 x 1/8 foam tape that exactly fills the gap between the Basement Safe’s door and liner:
The hinge side of the door has tape between the door liner and the safe wall, because that closes in compression rather than shear:
There should be a big bump in the humidity record marking that installation, but I don’t expect any immediate difference. If the silica gel lasts more than two months, I’ll consider it a win.
So I picked up a lot of 20 p-channel MOSFETs from the usual eBay supplier in China, which arrived in good order. As is often the case, the SOIC chips are in snippets of tape-and-reel carrier, but this tape looked decidedly odd:
Peeling back the tape shows that the crud is just on (or perhaps inside) the tape, not on the ICs or inside the carrier pockets:
Some of those specks are dirt, some seem to be bubbles, other are just, well, I don’t know what they might be. Maybe they were having a bad day in the tape factory?
One might reasonably conclude the chips aren’t in their original carrier…
I must gimmick up a quick test to verify that the chips behave like p-channel MOSFETs, instead of, oh, solid plastic; that Fairchild logo looks a bit grotty, doesn’t it?
The discussion following that post on getting feature coordinates from an existing part reminded me of an old project that I’d written up for Digital Machinist: making repair parts for the half-century old storm doors on our house. Here’s the whole latch, with a replacement drawbar and cam:
The other side of the drawbar and cam:
An early version of the drawbar that engages the latch strike and gets pulled by cam:
Three iterations on a cam; the messed-up one in the center, IIRC, helped track down an EMC2 bug:
Now that I look at it again, there’s nowhere near enough meat around that square hole for a 3D printed plastic part… so the notion of printing the complex part of the cam and adding wear bars along those ears just isn’t going to work.
I made a fixture for the Sherline CNC mill to hold the drawbar for inside milling:
Then a block screwed down in the middle clamps the drawbar in the same place for outside milling:
The square post in the left rear corner holds the cam:
Note that I had to file the square hole before milling the cam shape, which meant that if the CNC process screwed up, all that handwork went into the show-n-tell bin… which I’m not going to show you.
I used an early version of the grid-overlay technique to map out the drawbar coordinates; this was an illustration for the column:
A pack of humidity indicator cards arrived from far-off Pennsylvania and work just about like you’d expect.
The silica gel really does pull the interior of the Basement Safe down below 15%:
The dehumidifier struggles mightily to keep the rest of the basement around 50%:
They’re not dataloggers, but I can now keep an eye on more locations…
A bag of 50 cheap Hall effect sensors arrived from the usual eBay vendor, who was different from all previous eBay vendors (if in name only). Passing 124 mA through the armored FT50 toroid with 25 turns of 26 AWG wire, we find this distribution of bias points, measured as the offset from the actual VCC/2:
The bias point is actually referenced to the negative terminal (usually ground) with a ±0.25 V variation around the nominal. SS49 sensors run about 0.5 V below VCC/2 (2.25 V with a 5 V supply), SS49E sensors at 2.5 V with a tighter VCC limit that suggests you better stay pretty close to 5.0 V.
Allowing for the fact that I really don’t have good control over the actual magnetic field, the gain distribution seems tight:
You’ll recall the Genuine Honeywell sensor specs:
The gain is roughly half that of the previous “49E” sensors, confirmed by sticking one of them this field. I don’t know which is more accurate, but these have a much prettier distribution.
So this lot resembles 49E sensors in both bias and gain.
Given the bias variation, though, it’s obvious that a DC application must measure the zero-field output and apply an analog offset to the amplifier, because a twiddlepot setting won’t suffice. Most likely, you’d want to update the offset every now and again to compensate for temperature variation, too.
Tossing the outliers gives an average gain of 1.17, which would give results within 10% over the lot. Given that you don’t care about the actual magnetic field, you could calibrate the output voltage for a known input current and get really nice results.
If you were doing position sensing from a known magnet, you’d want better control of the magnetic field gradient.
The Smell of Molten Projects in the Morning 