Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Although it’s not obvious, the two blue 2431 Ω resistors just above the toroid are a divider that scales the switched battery voltage (from the p-MOSFET on their left) by 50% and sends it to input A0 on the Arduino Pro Mini board:
Figuring the actual battery voltage is straightforward:
get 10 bit ADC value with analogRead()
multiply by actual VCC (measured at 4.96 V for this board)
divide by actual voltage divider ratio (measured at 3.78/7.57)
Which, of course, reported the battery voltage was 4.116 V. Huh?
After spending far too much time poking the code with a sharp stick, I wired the divider to the (previously unused) A6 and A7 inputs and dumped the raw ADC counts for all three. The answer should be somewhere near 763, but the three values came out around 215, 667, and 750. Huh?
The A0 value is totally bogus, so I finally looked at the Arduino Pro Mini board:
Arduino Pro Mini clone – chip overview
Hmmm. It turns out A0 is the second pin back on the left side:
I slathered flux on all the pins, touched each one with a soldering iron, and it’s all good.
This is a knockoff Arduino Pro Mini board from eBay, of course, and the rest of the boards in that lot were OK. Their QC inspection almost certainly boils down to running the Blink sketch: if the LED blinks after the power goes on, ship it!
Blink doesn’t verify the analog inputs, which turn out to be wrapped around that corner of the package.
Shortly after we bought this kitchen scraper spatula (or whatever it’s called), the handle pulled out of the blade and left it sitting in a bowl of batter. That turned out to be unsurprising, given that neither side of the interface has any mechanical locking features. I rinsed the batter off, stuck some urethane glue inside, rammed the handle in place, and hoped for the best. Lacking any mechanical interlock and not bonding to either surface, the adhesive didn’t improve the situation.
So I recently added a pair of stainless 4-40 setscrews standing just proud of the handle’s surface that should dig into the blade and hold it in place:
After rebuilding the front end of the Samsung vacuum’s floor brush, I’d hoped that was the end of it; other than replacing the brush strips every now and again, it’s been cooperative. Recently, however, one of the wheels popped off, which revealed the minimal mechanism holding them in place:
Samsung Quiet Jet – floor brush wheel interior
Those four delicate latches have worn themselves and the hub to the point where they ride over the edge at the slightest provocation. I pulled both wheels off and packed three turns of insulated wire (one turn is visible in the photo, as it was an iterative process) around the outside of the clips, with the intent of restoring enough force to hold the wheels in place until we exhaust the lifetime supply of bags I bought for the thing…
Having just tightened the teeny screws that hold the joints in place for the first time since I glued it to the helmet, I’d say it’s working fine. The 2-56 elevation setscrew has worn a slight dent in the arc and the 3-48 azimuth screw worked slightly loose; the mirror didn’t fall apart, but the position wasn’t as stable as it should be.
If I ever re-do the design, I’ll try adding a recessed metal (brass?) strip along the top of that arc, as that’s the most finicky adjustment. Perhaps a shoe under the setscrew would be better?
Two years of road grit show up clearly against the yellow plastic, though:
Bike helmet mirror mount – two years
For the record, those 2-56 setscrews require 35 mil hex keys; as Eks reminds me, any design requiring those screws is just crazy talk.
Nothing too challenging and, as nobody else ever sees this side of the lid, not very pretty:
Brita Pitcher – reinforced lid screws
I probably should have added a brass reinforcement strip around the cracked plastic mounts, but JB Weld epoxy should be strong enough for this job all by itself. Assuming, that is, it can maintain a grip on the plastic; I’m hoping the various fractures will lock it in place.
The left temple mount of Mary’s five-year-old and staggeringly expensive titanium Silhouette glasses snapped. Here’s the intact right earpiece and the broken piece from the left temple (the lens is upside-down on the paper):
Silhouette frame – broken temple part
They’re just about ideal glasses, with nothing more than two lenses and three metal bits, but that means simple repairs don’t come easily. The Official Repair Price was about $120 to install a whole new earpiece, so, seeing as how she had these customized for computer work and wouldn’t be wearing them when anybody else was around, I got the job…
First off, mask the lenses with Parafilm to avoid scuffs:
Silhouette glasses – lens protection
Then cut out the broken part shown in the first picture. It’s attached to the lens with a U-shaped bit of transparent plastic that fits into the frame holes and captures its two peg legs; I used flush-cutting pliers to carve away the plastic bar on the inside of the lens.
The lens mount fragment is flat-out not reparable, but the broken end of the earpiece lies flush against the lens and is roughly circular. Even better, a 1/16 inch brass tube from the Little Box o’ Cutoffs fit the temple end perfectly: OD = 62 mils, ID = 35 mils.
The Little Box o’ Tiny Screws produced a pair of stainless steel screws (intended for the hinges in ordinary eyeglass temples) that also fit the holes in the lens and were precisely the right length, so the overall plan came together. The screws seem a bit over 1 mm diameter and I don’t have a nut for them, but epoxy is my co-pilot…
Line up and drill a pair of 47 mil clearance holes in that piece of 62 mil OD brass tubing, leaving barely 7 mil behind on each side:
Drilling brass tube
I may have to frame that picture…
Much to my astonishment, drilling those two holes worked on the first try. I’d chamfered the end with a #1 center drill while mulling over how all this would work out.
File off the screw heads to leave a thin plate:
Silhouette frame – temple mount parts
A dry fit shows how everything hangs together:
Silhouette frame – temple trial fit
The intact earpiece holds the lens at the proper angle on a flat surface, so as long as I can keep the repair parts in place on the lens, the temple angle will take care of itself.
I scuffed up the broken end of the earpiece to encourage a good epoxy bond, bent the edges of those flat plates around the tube, and cleaned everything with acetone. Tiny dabs of JB Weld epoxy hold the screws and the temple piece in the tube, with those little machinist’s squares encouraging the lenses to stay put:
Silhouette frame – mount curing
A day later, lay the lenses face down so the screws point straight up and dab on more JB Weld:
Silhouette frame – lens mount curing
Those dots aren’t quite as round as I’d like, but they’re the better part of 2 mm OD and I’m not complaining much. Note the nice fillet around the temple piece at end of the tubing.
Pause another day for curing…
Then file off the rough edges and peel off the Parafilm. It’s a bit on the garish side, but Mary preferred the Steampunk look over a crude paint job, particularly because it’s invisible from her side of the lens:
Three years ago I installed a 1.5 TB WD Elements USB drive as an external backup for the “file server” in the Basement Laboratory. The log files show that the drive started spitting out “short reads” early in October, which means the rust has begun flaking off the platters.
Repeated fsck -fyv /dev/sda1 runs produce repeated failures at various spots, so it’s not in good condition:
e2fsck 1.41.14 (22-Dec-2010)
Backup-1.5TB contains a file system with errors, check forced.
Pass 1: Checking inodes, blocks, and sizes
Error reading block 97649088 (Attempt to read block from filesystem resulted in short read) while getting next inode from scan. Ignore error? yes
... snippage ...
Pass 2: Checking directory structure
Error reading block 104039017 (Attempt to read block from filesystem resulted in short read) while reading directory block. Ignore error? yes
Force rewrite? yes
Directory inode 26009985, block #26, offset 0: directory corrupted
Salvage? yes
... snippage ...
Pass 4: Checking reference counts
Inode 25903223 ref count is 41, should be 40. Fix? yes
... snippage ...
Backup-1.5TB: ***** FILE SYSTEM WAS MODIFIED *****
736471 inodes used (0.80%)
10173 non-contiguous files (1.4%)
9367 non-contiguous directories (1.3%)
# of inodes with ind/dind/tind blocks: 119655/12234/0
142996292 blocks used (39.04%)
0 bad blocks
3 large files
276772 regular files
459614 directories
0 character device files
0 block device files
0 fifos
10377447 links
76 symbolic links (72 fast symbolic links)
0 sockets
--------
11113909 files
Given that rsnapshot lashes the daily backups together with extensive hard links, so that there’s only one copy of a given file version on the drive, I don’t know what 76 symbolic links might mean.
It’s been spinning up once a day, every day, for about 40 months; call it 1200 power cycles and you’ll be close. The usual runtime is about 10 minutes, giving the poor thing barely enough time to warm up.
One data point does not a curve make.
The warranty on new WD Element drives seems to be a year; I have no idea what it was slightly over three years ago, although I’m pretty sure it wasn’t more than three years…
The various desktop boxes around here get powered up once a day, too, but I tend to replace them every few years and have never had a hard drive failure; a few system boards have crapped out, though. The boxes acting as controllers for the 3D printers and the Sherline CNC mill have a much lower duty cycle.
