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.

Category: Electronics Workbench

Electrical & Electronic gadgets

X10 Controller: End of Life

X10 Controller Circuit Board

After 30-some-odd years, the X10 controller we’ve been using to turn off all the lights at bedtime finally stopped working. For the last few months it had been occasionally jamming ON, even when nobody pushed any keys, and the only way to reset it was pulling the plug.

The big silver can on the white cable is an ultrasonic mic, so perhaps the circuitry around that was getting cranky: the ultrasonic cleaner in the bathroom (which we use for eyeglasses) would reliably jam it. I think the controller was responding to the third harmonic of the 40-ish kHz cleaner power, delivered through the power line.

As you’d expect, all the electrolytic caps were shot; ESR for the big one was “open”, the smaller ones around 5 Ω. The capacitance values were entirely within spec, of course. I replaced all three.

X10 Controller keyboard

While I had the hood up, I cleaned the switch contacts, even though that probably had nothing to do with the problem. Back in the day, they used actual metal deformable domes, stuck under an adhesive layer that did a fine job of keeping the crud and dust out.

Put everything back together, fired it up, and it misbehaved the same way. I’d say we got our money’s worth out of it, though.

A replacement is on the order of $15 from the usual eBay suppliers, so it’s not the end of the world.

The new one probably doesn’t have the ultrasonic receiver, so it shouldn’t respond to the ultrasonic cleaner with the same enthusiasm.

2010-03-17
Ambient Room Light Intensity
The Totally Featureless Clock has been running continuously for the last few months, with a laptop dutifully recording its trace output. Occasionally the USB link will disconnect, but on the whole it works pretty well; the clock continues to run even when the USB link fails.

Here’s about three weeks of light intensity record. The red trace is the max value, green is minimum, and blue the current intensity. The min and max tend toward the middle, one count per hour, so they don’t stick at the extremes.

Light Intensity

The peaks represent daylight hours, zeros are overnight, and the overall scale is roughly logarithmic, more or less, kinda-sorta.

The general idea is that the LED brightness matches the room illumination, with the min & max values tracking the actual ambient light range to get the most benefit out of the TLC5916’s limited dynamic range.

You can spot the data dropouts where the red trace steps abruptly; it should decline smoothly from each peak and the peaks should be evenly spaced about 24 hours (1440 minutes) apart. Each minute generates three lines with the exact time, so it would be possible to futz around and timestamp each record, but …

The clock dumps the ADC values in hexadecimal, which gnuplot can’t handle, so a bit of preprocessing is in order.
```
cat *log > 0.txt
grep Light 0.txt > 1.txt
sed 's/Light: /0x/g;s/Min=/0x/g;s/Max=/0x/g' 1.txt > 2.txt
gnuplot
set key on right center
plot "2.txt" using 1 with lines lt 3 title "Light", (and so forth)
```
All in all, it seems to be working as intended. When I put it inside the case, I’ll probably have to increase the resistor to account for the dark-gray faceplate.
2010-03-12
DVD Player External Li-Ion Pack: A Pleasant Surprise!
A friend mentioned a sale at Overstock.com (likely gone by now) that offered an Initial RB-270 9 V, 5.4 Ah lithium-ion battery pack, with a built-in charger, for $16. The pack was intended to keep a DVD player alive for long enough to avoid back-seat mayhem on long trips (for those toting undisciplined brats, anyway), but I saw it as a plug-in replacement for the NiMH AA-cell packs I’ve been using with the HTs on our bikes.

The NiMH cells have been a major disappointment, as described there and there and there, with barely 1.5 Ah of capacity from nominal 2.4 Ah cells.

Much to my surprise, all three of the Li-Ion packs delivered pretty nearly their advertised ratings. I varied the discharge level, but they’re all quite close…

Initial External Li-Ion packs

It looks like the packs include an internal regulator and over-discharge monitor, as the voltage is bar-flat right up to the point where it drops to zero. I’m mildly surprised at the regulator; I’d expect that they’d just deliver whatever the cells were producing, rather than waste any energy in the regulator.

Notice that the 200 mA rate produced a lower total capacity than the 1 A rate. I’m guessing that’s power lost in the regulator over the protracted run time; 4.9 Ah at 200 mA added up to nearly a day of testing, far over the “up to six hours play per charge” rating.

Let’s see: 5.4 Ah @ 6 hours makes the nominal load about 900 mA. So it delivered maybe 4.8 Ah at 1 A. Not what’s claimed, but much closer than those Tenergy NiMH cells.

Next steps:
1. Butcher the nice coily-cord cables to add Powerpole connectors that will click right into the bike radios
2. Take one apart to see what bypassing the regulator would entail
2010-02-22
Cutting Pin Header Strips

Slitting dual-row connector

I needed a few strips of single-row pin headers, but the parts bin was empty.

I hate it when that happens.

The heap disgorged a handful of double-row strips and, of course, I Have A Machine Shop.

So: no problem.

This is, I admit, not cost-effective, but it took about 15 minutes to slit the aforementioned handful of strips right down the middle and get back to soldering.

The trick is to use an ultra-thin slitting saw, rather than a regular saw. The one here is 4 mils thick and the better part of 7/8″ in diameter; call it 0.1 mm x 22 mm. I think it came with one of the Dremel tool kits a long while ago.

Cut about 1 mm deep on the first pass, then cut through on the return to avoid having the saw deflect too much. Run about 100 mm/min, 1000 rpm, and no coolant. Line it up by eye, type manual CNC commands into EMC2, and it’s all good.

The trick is finding a mandrel that doesn’t collide with the vise; my larger saws have a rather thick screw-and-washer arrangement that doesn’t fit. I think some padding (chopped-up credit cards?) between the longer pins, mounting the vise vertically, and grabbing the longer pins would fix that. The catch might be clearance between the top of the vise and the bottom of the spindle motor.

Better to just buy some single-row strips. Sheesh… but if all you have is a CNC mill, you have plenty of solutions.

Another slitting saw repair is there…

2010-02-13
Digikey Full-Line Catalog

For the first time ever, Digikey sent me a full-line catalog.

Digikey catalog

It’s 2778 pages long, three inches thick, and weight 2 kg.

Some time ago I made the mistake of replacing our large rusted-out mailbox with a much smaller one: the catalog presented a solid wall of paper when I opened the door.

Here’s a closeup…

Digikey catalog vs Arduino Duemilanovae

Now, I’d love to have you believe I’m such a high-rollin’ kind of engineer that Digikey spares no expense on my behalf, but the only explanation for this embarassing situation I can come up with is that their customer service system blew a gasket in my general direction…

What makes it even more ironic is that they’d recently sent me a survey asking how I’d like to get their catalog. I’d emphatically replied that I did not need a paper catalog or a USB stick with the PDFs. Just let me do the on-line searching and occasionally refer to the appropriate PDF pages and I’ll be fine.

The damned thing is basically useless; I hate to just toss it in the recycling, but I can’t think of any reason to keep it around.

I just removed my mailing address from their list, presumably leaving my account info intact; we’ll see if that sticks.

2010-02-12
TLC5916 Minimum LED Current

The TLC5916 datasheet seems to say that the minimum regulated LED current is 5 mA, but that’s painfully bright at, say, 12:08 in the early morning. Indeed, those 3-inch blue LED digits lit up the entire house from the living room… sometimes, a high-efficiency LED isn’t what you need.

This graph from the datasheet suggests that the current can be somewhat lower:

TLC5916 Current vs Rext

With that in mind, I replaced the 1 KΩ resistors with 3.9 KΩ parts.

The graph says the maximum current should be around 5 mA and, indeed, the formulas indicate 4.7 mA. The minimum current is a paltry 0.4 mA: lo and behold, the early morning illumination became bearable. After I put the LEDs behind some dark-gray polycarbonate, it’ll be just about perfect.

If it’s too dark, I can always solder another SMD resistor atop the 3.9 KΩ chips.

I figured out how to compute Rext somewhat more easily than the datasheet would have you believe and documented the process there.

2010-02-10
Tour Easy Recumbent: Amateur Radio HT Mount
Mary sewed up a new seat cover for her Tour Easy, so I dismantled the seat and cleaned things up. This is a good opportunity to show how I mounted an amateur radio HT on the bike…

Bottle holder on seat frame

Clamp mount detail

The general idea is simple: a water bottle holder attached to the lower seat rail with a circumferential clamp made from a chunk of half-inch aluminum plate. An aluminum spreader adapts the wider hole spacing on the bottle holder to the teeny little clamp.

With the bottle holder in place, I put the radio in a wedge seat pack, atop a block of closed-cell foam to more-or-less cushion some of the bumps. The wedge pack seatpost strap secures it to the bottom of the holder and the rail straps wind their way through the holder and lash around the aluminum spreader plate. It doesn’t move very much at all.

The radio is a long-obsolete ICOM IC-Z1A, bought specifically for this purpose: it has a remote head on the end of a coily cord. That puts the power, volume, and channel buttons out where you can actually use them.

Radio in seat wedge pack in bottle holder

The lump behind the seat looks moderately suspicious in this day & age: a black package with wires! The grossly oversized red-and-black pair in the foreground is the power coming from a 6-AA pack attached to the rack with a Velcro strap; it’s a jumper with Anderson PowerPoles on both ends. Coily cord to the HT head, BNC-to-UHF adapter to the mobile antenna mount, one skinny cord to the headset and the other to the PTT button on the handlear.

Other pieces of the puzzle:
2010-02-08