goatee-stroking musing, or something

Resurrecting a fine old meter

I picked up a fine-looking ex-Forces Bach-Simpson 635 multimeter from Active Surplus the other week.

Simpson Canada 635After opening it up and cleaning out all the corroded battery gunge, it cleaned up pretty well:

The guts of a Simpson Canada 635

The needle would only go about ⅖ full range, though. Carefully opening up the front showed that the corrosive goo had got into the meter movement itself:

Corrosion inside meter coreSince the meter was pretty much useless as is, I carefully scraped away at the green gunge on the stator. This freed up the moving coil, so the meter now works pretty close to how it should. Clock that dial!

Clock that dial!Simpson 635 Armed Forces Identity PlateI took the HV back off the meter. There’s no way I’m going near 6 kV with this meter. Anything over 12 V makes me worried …

computers suck

X10 for Raspberry Pi on the Cheap [North American Edition]

Now I’ve got my X10 system running and know its limitations, I could have saved a wheen of money not buying stuff I don’t need. Our house appears to have been wired by an, um, spirited amateur, so powerline signalling is of limited use. Thankfully, the tiny and cheap X10 FireCracker CM17A (warning: too many flashing GIFs at this link!) can be driven from heyu [previously]. You can score these on eBay for under $10, and all you need is a serial adapter to drive them.

Leviton X10 controller - cheap!The really cheap bit in my system was discovered in Active Surplus. I found a case of Leviton “Plug-in Frequency Transceiver Modules” for $4/each. One was out of its case, and wouldn’t you know it, it’s the same as a RR501 module, which typically retails for about $30. Sure, these are old stock and are a nasty beige colour, but they provide a way of switching a two-pin appliance. They can also relay remote commands from RF to wired controls.

The only X10 controller I can’t get to work with the Raspberry Pi is the CM19a USB PC Transceiver. I suspect it draws a bit too much power to run from a Raspberry Pi, as it makes the machine unresponsive if it’s plugged it. Running from my bench setup it works fine with the mochad driver, but no dice with the other machine. The CM19a reads wireless RF X10 commands, and it would be useful if I’d added a motion sensor. As is, I’ll stick to the lights going on and off.

(Update: there’s a good chance that my CM19a problems are down to the ancient dwc_otg* fixes I still run on my Raspberry Pi’s kernel. You probably don’t need them, and this device could work fine. One day I will find time to fix ’em …)

(Incidentally, this is the “North American Edition” because X10 RF controls are completely different in Europe, and none of the above is useful to you. Yeah, I know this article is the equivalent of PC Load Letter to you; sorry.)

goatee-stroking musing, or something

yay tiny stepper motor!

Active Surplus Electronics is the best. I was wanting to learn about driving stepper motors from a microcontroller, but didn’t want to spend a lot or rig up a complex power supply. Active Surplus had a bin of tiny 5V stepper motors at under $3 each. The one I bought is marked:

50-03500-    028
 MALAYSIA   7115

I have no data sheet, but I’ve been able to work out that it’s a unipolar stepper motor, 20 steps/revolution (18°/step; quite coarse), wired:

  • Centre tap: Brown
  • Coil A: White, Red
  • Coil B: Orange, Blue

It’s small enough to be driven directly by USB power through an Arduino and the Adafruit Motor Shield. No idea how much torque this thing puts out, but it can’t be much.

(Setting up my motor shield was a pain, as I’d accidentally put non-stacking headers on it. This required an hour of swearing-filled desoldering; lead-free through-hole desoldering is just the worst*. With wick and solder pump, I finally managed to clear everything up well enough to fit the new headers.)