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January 12, 2008
C, Java, XSLT, assembler
Vacuum tubes, neon, microcontrollers, electronics
Neon, reading, building, making
News - Enginursday: Innovative T…
about 5 days ago
Strapping to connect the level shifter to V1 or V2?
News - Friday Product Post: Lase…
about a week ago
There is an IR interface for X-10 (IR543 or IR7243), I imagine this would work with it.
News - Introducing "Old Mac…
about 2 months ago
There’s a fair amount of interest in old Heathkit gear. They made a bunch of cool TV test stuff, and while analog TV isn’t broadcast much any more, people still find use for it. What do you have? Pattern generator? Vectorscope? VTVM? GDO? Demodulator probe?
I was guessing the other tube was a 6C4, and sure enough, it is. It’s basically half a 12AU7. You can find the manual here: http://tubularelectronics.com/Heath_Manual_Collection/Heath_Manuals_S/SG-8/SG-8.pdf Sure enough, that connector isn’t a PL-259, just a generic microphone connector which was pressed into service for a lot of test gear (VTVMs, oscilloscopes, etc.) back in the day. Everybody made ‘em, but I don’t know of a standard name. It’s probably a 5/8-27 thread, like Amphenol 85-75MC1F, Switchcraft 2501F, or J-30.
News - ATP: Hall Effect and Lore…
about 5 months ago
Oops, I missed a word: aluminized mylar: a very thin layer of aluminum on a mylar substrate. I tried cleaning off the decorations with flux remover, which worked fairly well, then I cut out the sensor shape, which was an amazingly fiddly process, with the very thin material that wanted to curl up. Then I removed the label from a Sparkfun box with a heat gun, which left a sticky surface to which I adhered the aluminized mylar. Then I used 4-40 nylon screws to attach strips of copper foil to the corners and hooked it all up. No dice. While I had measured some pieces of it and got very low resistance (fractions of an ohm), the piece I had made appears to have discontinuities in it, probably scraped the aluminum while scrubbing/cutting/attaching it. It really is thin aluminum, I can see light through it. I think I’ll go shopping for a non-printed aluminized mylar balloon or one of those “space blankets”, which might not be as ready to curl up.
As for the Thomson galvanometer, we do have the advantage these days of small, lightweight lasers, so you don’t have to wait for a sunny day and arrange everything just right to get a beam. That would be a wonderful combination of old and new technology!
I’m still playing with it. I built a transimpedance amplifier out of an LF356 and hooked it to a meter to yield a much more sensitive meter. I’m powering it from a 9V battery for both low noise and so I can float it at whatever voltage is required. Pushing a microamp into it gives good meter deflection. I’m playing with a mylar balloon to get a thin enough foil. I’ve verified that it’s conductive, but I’m having trouble making good contact with it, as this particular balloon is decorated and the ink isn’t conductive. I’ll see if I can remove it with solvents, but I may have to go buy a plain silver one to play with. I’m also thinking I could buy some fake gold leaf from eBay and try that. I figure I can make contacts with either conductive paint, or try lightly clamping copper foil for leads using something like plastic paper clips – I learned my lesson about using anything ferrous anywhere near the big magnet!
News - Enginursday: Sparking Cre…
about 5 months ago
I had a board like that, where I had lifted some of the circuitry from an open-source product. Eagle told me there was an issue there, but it was a working board, so I approved it and sent it off to fab. Sure enough +3.3V was shorted to ground: right in that borrowed layout. It took a little while to narrow it down, cutting traces here and there and using a short tracer. The next revision, I paid more attention to the DRC errors!
I made a go at it. First I tried aluminum foil, but I couldn’t solder to it, so I connected it up with alligator clips. I rounded up my most sensitive ammeter (5µA full scale), hooked it one way, and hooked a bench supply the other (perpendicular) way and ran 1 ampere through it (checking to see if some asymmetry in my setup pushed some current through the meter, but it didn’t) and waved a powerful magnet at it. The powerful magnet yanked all the clips up! I was afraid I’d ram an amp through my sensitive meter and destroy it! Therefore I made another unit of copper foil, soldered wires to it, and set everything up again. I tried waving the magnet, and saw a little deflection! Then I switched off the bench supply and saw the same deflection. It turns out the magnet was affecting the nearby meter. I spaced everything well apart and tried again. No deflection. I realized the light galvanometer Hall used was effectively magnifying the meter deflection, so I tried observing my meter under a microscope, and saw a small deflection! I turned off the bench supply and saw the same deflection: I was observing Henry’s law, I was inducing current in a conductor with a moving magnetic field, not deflecting electron flow with Lorentz force. Cool, but not what I’m looking for. I figure the Hall effect is a pretty low-impedance source (it’s a piece of copper foil), so perhaps I’ll try boosting it with a transimpedance amplifier next. I may also try some different geometries of copper foil (these tests were done with a square piece, with the wires connected to the corners).
“Entirely built of problems”, now that is a beautiful turn of phrase!
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