Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
As you might expect, the cable saws through the side of its ferrule and the brazed-on frame fitting, because it’s been basically impossible (for me, anyhow) to find a replacement derailleur duplicating whatever the good folks at Easy Racers shipped back in 2001.
On the upside, this derailleur’s cable entry has a nicely rounded ramp eliminating the need for my brass cable pulley widget.
Memo to Self: Perhaps running the cable around a bearing anchored to the frame fitting would help?
I’ve obviously forgotten to fix this for several years, so putting it here may serve as a Round Tuit.
When they happened, I knew where to look, because the Kevlar-belted Primo Comet had two conspicuous bulges surrounding debris jammed between the tread and the carcass along the sidewall: the gashes were wide open!
Much to my astonishment, the tire hadn’t gone instantly flat.
Some screwdriver probing in the leftmost gash produced this nasty glass chip:
Primo Comet gash – chip side view
AFAICT, the smooth side slid over the internal Kevlar belt as the edge sliced between the rubber tread and the carcass. I think the top entered first, with the somewhat crushed end hitting the pavement on each revolution:
Primo Comet gash – chip edge view
The other gash emitted a somewhat smaller chip.
I rode over something crunchy, most likely the remains of a beer bottle, in a shaded section along Rt 376, and we stopped a few driveways later to diagnose a once-per-revolution thump from the front tire. The tube still wasn’t losing pressure, even after extracting the glass, so I continued the mission; it was a fine day for a ride!
I later filled those gashes (plus a few others) with silicone rubber to keep grit out. It’s surely a feel-good gesture, but maybe it’ll help the tire reach the end of its tread life.
You can judge our “riding environment” by the tire’s condition …
Poking the Print button on the front of the Siglent SDS2304X scope saves the screen to a BMP file (in the /BMP directory) on a USB flash drive plugged into its front-panel port:
Siglent SDS2304X Front Panel – Print Button – USB port
Which produces files like these:
ll --block-size=1 /path-to-USB-stick/BMP/
total 2318336
drwxr-xr-x 2 ed ed 4096 May 23 13:13 ./
drwxr-xr-x 4 ed ed 4096 Dec 31 1969 ../
-rw-r--r-- 1 ed ed 1152054 May 23 13:13 SDS00001.BMP
-rw-r--r-- 1 ed ed 1152054 May 23 13:13 SDS00002.BMP
The files are 1152054 bytes long, as specified by the BMP header inside the file:
hexdump -C /path-to-USB-stick/BMP/SDS00001.BMP | head
00000000 42 4d 36 94 11 00 00 00 00 00 36 00 00 00 28 00 |BM6.......6...(.|
00000010 00 00 20 03 00 00 e0 01 00 00 01 00 18 00 00 00 |.. .............|
00000020 00 00 00 94 11 00 00 00 00 00 00 00 00 00 00 00 |................|
00000030 00 00 00 00 00 00 01 01 01 01 01 01 01 01 01 01 |................|
00000040 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 |................|
*
00000880 01 01 01 01 01 01 01 01 01 01 01 01 01 01 1e 1e |................|
00000890 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e |................|
*
00000990 1e 1e 1e 1e 1e 1e 01 01 01 01 01 01 01 01 01 01 |................|
The first 14 bytes contain the Bitmap file header, with the file size in Little-Endian order in the four bytes at offset +0x02: 0x00119436 = 1152054.
The four bytes at offset +0x0A give the offset of the pixel data: +0x36. That’s the series of 0x01 bytes in the fourth row. Unlike most images, BMP pixel arrays start at the lower left corner of the image and proceed rightward / upward to the last pixel at the upper right corner.
The data between the Bitmap file header and the start of the pixel data contains at least a Device Independent Bitmap header, identified by its length in the first four bytes at offset +0x0E. In this case, the length of 0x28 = 40 bytes makes it a Windows (no surprise) header.
The two bytes at +1C give the bits-per-pixel value: 0x18 = 24 = 3 bytes/pixel, so parse the pixels in RGB order.
The four bytes at +0x12 give the bitmap width in pixels: 0x320 = 800. Each pixel row must be a multiple of 4 bytes long, which works out fine at 2400 bytes.
The tail end of the file shows one dark pixel at the upper right:
hexdump -C /path-to-USB-stick/BMP/SDS00001.BMP | tail
00118330 00 cc 00 00 cc 00 00 cc 00 00 cc 00 00 cc 00 00 |................|
00118340 cc 00 00 cc 00 00 cc 00 00 cc 00 00 cc 00 00 cc |................|
00118350 00 00 cc 00 00 cc 00 00 cc 0f 0f 75 1e 1e 1e 1e |...........u....|
00118360 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e |................|
*
00118ad0 1e 1e 1e 01 01 01 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e |................|
00118ae0 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e |................|
*
00119430 1e 1e 1e 01 01 01 |......|
Which looks like this, expanded by a factor of eight (clicky for more dots to reveal the situation):
Screenshot – upper right corner – 8x expansion
The scope can also transfer a screenshot over the network:
lxi screenshot -a 192.168.1.42 /tmp/lxi-shot.bmp
Loaded siglent-sds screenshot plugin
Saved screenshot image to /tmp/lxi-shot.bmp
Which has the same header:
hexdump -C /tmp/lxi.bmp | head
00000000 42 4d 36 94 11 00 00 00 00 00 36 00 00 00 28 00 |BM6.......6...(.|
00000010 00 00 20 03 00 00 e0 01 00 00 01 00 18 00 00 00 |.. .............|
00000020 00 00 00 94 11 00 00 00 00 00 00 00 00 00 00 00 |................|
00000030 00 00 00 00 00 00 01 01 01 01 01 01 01 01 01 01 |................|
00000040 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 |................|
*
00000880 01 01 01 01 01 01 01 01 01 01 01 01 01 01 1e 1e |................|
00000890 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e |................|
*
00000990 1e 1e 1e 1e 1e 1e 01 01 01 01 01 01 01 01 01 01 |................|
But the resulting file is three bytes = one pixel (!) too large:
ll --block-size=1 /tmp/lxi.bmp
-rw-rw-r-- 1 ed ed 1152057 May 23 19:09 /tmp/lxi.bmp
The tail end of the file:
hexdump -C /tmp/lxi.bmp | tail
00118330 00 cc 00 00 cc 00 00 cc 00 00 cc 00 00 cc 00 00 |................|
00118340 cc 00 00 cc 00 00 cc 00 00 cc 00 00 cc 00 00 cc |................|
00118350 00 00 cc 00 00 cc 00 00 cc 0f 0f 75 1e 1e 1e 1e |...........u....|
00118360 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e |................|
*
00118ad0 1e 1e 1e 01 01 01 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e |................|
00118ae0 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e 1e |................|
*
00119430 1e 1e 1e 01 01 01 01 01 0a |.........|
Because the file header doesn’t include those three bytes, they don’t go into the image and the resulting screenshot is visually the same.
Which looks like a picket-fence error, doesn’t it? I’d lay long odds the erroneous loop runs from 0 to NUMPIXELS, rather than 0 to NUMPIXELS-1. Raise your hand if you’ve ever made that exact mistake.
I have no practical way to determine whether the error is inside the scope or the LXI network code, but given Siglent’s overall attention to software fit-and-finish, I suspect the former.
One can convert BMP files to the much more compact PNG format:
convert /tmp/lxi.bmp /tmp/lxi.png
convert: length and filesize do not match `/tmp/lxi.bmp' @ warning/bmp.c/ReadBMPImage/829.
Yes. Yes, there is a mismatch.
The space savings is impressive, particularly in light of PNG being a lossless format:
ll /tmp/lxi.*
-rw-rw-r-- 1 ed ed 1.1M May 23 19:09 /tmp/lxi.bmp
-rw-rw-r-- 1 ed ed 14K May 23 19:17 /tmp/lxi.png
For the record, a 5/8 inch socket works fine. One could surely use a 16 mm socket in a pinch.
Wear leather gloves to prevent a nasty gash from the stamped-steel muffler shroud as you pull the sparkle plug cap to avoid an absolutely impossible engine startup while you’re wrenching under the deck.
Littelfuse Mini Auto Fuse Puller-tester – as opened
Somewhat to my surprise, the other side of the PCB has components:
Littelfuse Mini Auto Fuse Puller-tester – circuitry
It looks like a transistor switch to minimize the current through the fuse and protect the LED from over / reverse voltage, should you apply it to a live circuit.
A pair of new cells had it working just fine, not that I expect to need it in real life.
The first white LED fixture built to illuminate one of Mary’s Kenmore 158 sewing machines has been in regular use for the last four years:
Kenmore 158 Sewing Machine – mixed LED lighting
We never found a good time to rip-and-replace the “prototype” with brighter SMD LEDs and one of the LEDs finally gave up.
They’re 10 mm white LEDs with five chips wired in parallel, which is obvious when you look into the remaining LED running at 1 mA:
10 mm white LED – chips
The center chip is just dimmer than the others, which means their QC doesn’t tightly control the forward voltage spec.
The wire bonds on the anode terminal of the failed LED look a bit sketchy:
10 mm white LED – wire bonds
Fortunately, I hadn’t removed the 120 VAC wiring for the original bulb and I have two OEM bulbs from other machines, so I just removed my LED gimcrackery, installed a good old incandescent bulb, and she’s back to sewing with a pleasantly warm machine.
The fixture holding the LEDs broke apart as I extracted it, but it’ll never be used again:
10 mm white LED – fixture
The LEDs are rated at 3.5 V and 200 mA (!), but were reasonably bright in series from a 6 V unregulated supply. Perhaps a power glitch killed the poor thing? We’ll never know.
LEDs are reputed to have lifetimes in the multiple tens of thousands of hours, but I’ve seen plenty of failed automotive LEDs and fancy new LED streetlights out there, not to mention many dead and dying traffic signals. Seeing as how they’re in (presumably) well-engineered fixtures with good power supplies and are at most only a few years old, there shouldn’t be any failures yet.
The back tire on my bike was flat when I rolled it out for a ride (the day after replacing the front shifter cable), which ought not be possible with a Michelin Protek Max tube inside. On the other paw, we’ve had zero flats in the not quite two years since installing the things, which says they’re doing very well, and I’ll take a flat in the garage over a flat on the road any day.
With the bike up on the stand, I didn’t spot the expected large glass chip or sharp wire, but I did find three smaller gashes:
Bike tire tread gashes – composite – 2017-05-13
… from which I extracted two small glass shards. Perhaps a wee puncture spent four days parked at the top of the wheel, with the ProTek’s internal goop drained away and unable to plug the slow leak.
Having spun the tire a few times while looking for trouble, I pumped it back up to 80 psi. After delaying the ride for half an hour, the tire pressure remained constant, and we enjoyed a fine ride around the block.
Because I’m writing this in the future, I know it’ll hold pressure just fine, which means I can declare victory and move on.
The tube & tire weigh more than some frames, but they’re worth it!
The Smell of Molten Projects in the Morning 