Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
A surplus haul of 24 V / 150 mA white LED panels arrived:
LED Panel – 24 V 150 mA
I wired a pair to a 24 V wall wart and stuck them under the M2’s bridge supporting the X stage:
LED Panel – on M2 Gantry
I thought about epoxying them in place to get better heatsinking to the metal bridge. The ever-trustworthy description said the big copper baseplate meant the panels didn’t need any heatsinking, so I used tapeless sticky and will hope for the best. Should the sticky give out, then I’ll use epoxy.
They’re much better than the previous white LED strip, although it’s tough to tell in the pictures. The chain mail armor appears under the new lights; some older pictures will creep in from time to time.
We’ve been doing a lot of roasting and bought a not-dirt-cheap Taylor 1478 digital kitchen thermometer with a long probe wire to monitor the meat temperature. As soon as I unpacked it, I knew this would eventually happen:
Kitchen thermometer – nicked probe wire
The cable lasted just long enough to ensure the thermometer warranty expired; it’s a deliberate design flaw if I’ve ever seen one.
The thermistor inside the probe seems to be 100 kΩ at ordinary temperatures, although I’d be completely unsurprised to find that Taylor uses a slightly nonstandard resistance. Because nonstandard, of course.
Anyhow, replacement probes (*) are readily available from the usual Amazon suppliers, feature stainless steel braid sheathing and cost about as much as a whole new thermometer (albeit those still have cheap plastic insulation). With a replacement on order, I hauled the failed probe to the shop for an autopsy and possible resurrection…
Although I hoped that hammering out the crimp would release the thermistor, it was not to be. In retrospect, pulling on the probe wire probably killed it, but I didn’t know that at the time.
A spring intended to stabilize tubing while bending worked just fine to un-bend the probe:
Kitchen thermometer – unbending
But, alas, the thermistor still didn’t emerge from the more-or-less straightened probe.
Some deft work with a Dremel cutoff wheel sliced enough off the stainless steel tube that I could splice the wires:
Kitchen thermometer – probe cutting
More cutoff wheel work smoothed the edges of that raw cut end, although the result wasn’t anything to show off.
The spliced and insulated probe definitely don’t win any awards, either:
Kitchen thermometer – probe rebuild
I doubt that the heatshrink tubing or silicone wrap underneath it would be suitable for roasts in the kitchen, but that’s moot: the probe remained intermittent.
If the new probe is also intermittent, then I’ll suspect the crappy 2.5 mm jack in the side of the thermometer…
(*) It’s not clear that a replacement probe for a 1470N thermometer will work with a 1478 thermometer. I’m gambling that Taylor wouldn’t be so stupidannoying deliberately obtuse as to use different probe thermistors, but that’s surely a bad bet. There’s no reason to believe Taylor actually makes any of this stuff, which means different models may come from entirely different designers / factories with entirely different supply chains.
It seems the batch of Energizer CR2032 lithium cells I bought a while ago reached the end of their shelf life:
Energizer CR2032 – short life
In point of fact, I replaced three CR2032 cells this month, all with anomalously short lives: one month counts as a complete failure. The Energizer date code YA isn’t helpful in determining when they were manufactured or what the shelf life might be.
Admittedly, I bought that batch in late 2009, so they might have used up most of their shelf life on somebody else’s shelf. There’s no way to know.
It’s not clear one can buy known-good cells from any supplier these days, as the counterfeiters evidently get genuine holograms from the same factory as the Brand Names.
From a surplus batch, with no provenance, measuring the resistance with current increasing (upper = squares) and then decreasing (lower = diamonds):
NTC 2.5 Resistance vs Current
The resistance at a given current need not lie between those bounds, because it depends strongly on the thermistor’s temperature (duh), which depends on heat loss to the surroundings.
With that in mind, 1 or 2 Ω looks like the right ballpark for these gadgets. Figure around half a watt each at 600 mA; string three in series to get 9 Ω during a cold start and 3 Ω for warm starts. It’s not clear that would solve the transistor killing spike, but it’s a thought.
Compared to the SCK055 NTC thermistor, they have about the same resistance at the same current, despite starting at half the initial cold resistance. I think that’s because they’re somewhat larger and thus run cooler at a given current.
The original data and a portrait of the thermistor:
NTC 2.5 Power Thermistor – measurements
Anybody recognize the logo? The symbol in the striped triangle is S+M, if that helps.
A friend reported that three of the four heating blankets he’s bought over the last several years have failed, so he sent the lot to me for teardown and maybe repair.
Looking inside one controller showed some obviously bad solder joints:
Blanket controller – bad joints
Hitting the joints with the soldering iron improved their outlook on life, but the controller remained dead; they weren’t really bad joints, they just looked that way.
If the “lot number” labels on the controllers mean anything, they’ve tried three different triac mounts over the years:
A through-hole triac screwed to the board with no heatsink
An SMD triac using the PCB copper as a heatsink
A through-hole triac with a big aluminum heatsink
That’s in order of ascending lot number, suggesting the triac caused some reliability problems.
I’m still trying to figure out how to probe the circuitry without killing myself. An isolation transformer comes to mind, because the blanket dissipates only 85 W.
With the Sony HDR-AS30V in its skeleton frame atop my bike helmet, the audio track for all my rides consists entirely of horrendous wind noise. You can get an idea of the baseline quality from the sound track of a recent Walkway Over The Hudson crossing.
The camera has two mics, although I’m not sure 15 mm of separation really produces meaningful stereo sound:
Sony HDR-AS30V – front view
Note that two of the five pores on each side are closed flat-bottom pits. As with earbud vents , it must be a stylin’ thing.
I added a rounded pad of the same acoustic foam that forms an effective wind noise buffer for the boom mic:
Sony HDR-AS30V – foam mic cover
That reduced the overall noise load by buffering direct wind impact, but non-radio conversations remained unintelligible; there’s just too much low-frequency energy.
Surprisingly, closing the mic pores with ordinary adhesive tape didn’t impair the audio in a quiet room:
Sony HDR-AS30V – closed mic pores
Out on the road that’s even better than foam over open mic pores; I think it reduces the peak volume enough that the internal compression can regain control. Sticking the foam pad over the tape slightly reduced the noise during high-speed (for me, anyhow) parts of the ride, but didn’t make much difference overall.
The wind noise remains too high for comfort, even if I can now hear cleats clicking into pedals, shifters snapping, and even the horrible background music when I’m stopped next to the Mobil gas station on the corner.
While pondering the dead ET227 transistors, I dug an inrush current limiter (a.k.a. NTC power thermistor) out of the heap and made some measurements:
SCK055 NTC Power Thermistor – measurements
That’s from a bench power supply attached to a meter and the limiter with clip leads, which was entirely too messy for a picture.
Turning those numbers into a spreadsheet to calculate the resistances:
SCK 055 NTC Power Thermistor
5 Ω @ 25 °C
Imax = 5 A
Time constant on the order of 90 seconds
Current mA
Initial mV
Final mV
Initial Ω
Final Ω
36
190
5.3
65
350
5.4
95
500
5.3
124
638
5.1
153
770
5.0
180
880
790
4.9
4.4
210
910
870
4.3
4.1
242
980
4.0
260
1025
944
3.9
3.6
520
1500
1090
2.9
2.1
710
1430
1066
2.0
1.5
1010
1320
1050
1.3
1.0
910
1020
1.1
709
920
1030
1.3
1.5
1010
1480
1040
1.5
1.0
30
52
110
1.7
3.7
The data sheet recommends a minimum current above 30% of the maximum, which would be 1.5 A. That’s above the motor’s 1 A operating current, let alone the low-speed current limited conditions, but in this situation that just means the resistance will remain around 1 to 2 Ω with the motor chugging along.
If I had more of ’em, I could put them in series to build up the resistance, but it’s not clear why that would be better than, say, a 6 Ω aluminum-heatsink resistor dissipating a few watts.
The Smell of Molten Projects in the Morning 