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Member #134773

Member Since: May 19, 2010

Country: United States


I started playing with electronics in the mid-1960s, and with computers shortly after Neil Armstrong took “one small step”. I got a degree in CS in 1980, and started working then as an engineer.

  • OFF TOPIC I’ve been meaning to mention it here, but haven’t had the time. A few days ago, I saw a news report on TV that the Feds now have dogs trained to sniff out electronics. Although they claim it’s being used for sniffing out child porn (Google electronic sniffing dog), it seems to me that Big Brother could use these puppies (pardon the pun) to go after (and punish [OK, I couldn’t resist such an obvious additional pun at this point]) other non-main-stream uses of electronics, were they so inclined. Despite the puns, it seems to me to be pretty scary.

  • The thought occurred to me on my way to Field Day that these might make good computers for logging ham radio contacts, especially given their low power consumption. However, it would be a good idea to check them for RFI – though some careful application of copper tape to the inside of the case would likely go a fair ways to mitigating RFI problems.

  • How about a link for the datasheet for the “fuel gauge” (the BQ27441-G1) chip on the “Babysitter” page? Some may want to use this with something OTHER than an Arduino. (Can you say “Raspberry Pi” or “Edison”?)

  • When I first saw this, I was worried about a problem we ran into at a company I used to work for, to wit, that the “smart” lithium ion battery charger would completely shut down after being “on” for roughly 24 hours. Our customers would leave their systems plugged in for weeks on end, then decide to “untether” and get a nasty surprise that the battery was dead.

    So I started looking through the datasheet for the chip (the BQ27075) and was pleased to find section which talks about recharge voltages.

    I know that in many of my apps (“IoT” type gadgets) I like to use a LiPo battery for backup, and around here, I’d guess (I haven’t measured it) we average roughly 6 months between power outages. I’ll have to consider this one for future projects!

  • One other thing: at about 4:12 into the video, you are talking “giga ohm resistors” – it seems to me you’ve probably mis-read the code, as that would be higher than the trace-to-trace resistance of the printed circuit board.

    Also, I suspect that the thing over in the corner, at about 2:15 into the video, that you’re guessing is a “wave rectifier”, is likely something along the lines of an SCR that the unit uses to control the power to the actual blanket. After all, the control unit is basically just a glorified light-dimmer.

  • OK, now that I’m back from the eye doctor (still a bit blurry), looking at the DigiKey site mentioned elsewhere (and their datasheet), I’d say that something around 150K to 200K ohms is a good guess. (I’ve seen manufacturing errors where a 150 ohm resistor is substituted for a 150K – which lets the “magic smoke” out of things.)

    Anyway, 120V across a 150K resistor is going to dissipate 0.096 watts, so assuming there’s a zero voltage drop on the lamp (not likely!) a ¼ watt resistor is overkill.

  • In my experience (dating back a half century), ½ watt ballast resistor is plenty at 120V (or even 240V) for a small neon lamp. (Back when neon lamps were common, ½ watt resistors were by far the least expensive. A ¼ watt cost maybe 4x what a ½ watt back in those days, so you’d only use the ¼ watt if you needed the small physical size.) (You might need a 1 watt if it’s powered by 1kV or higher – I have seen that, though usually the neon lamp is there to “bleed” the high voltage down to something safer when power is removed.) I’d be suspicious that either the lamp actually failed (I have seen one or two short), and/or the wrong ballast resistor got put into place. (I’ve got a Dr. appointment to get to so don’t have time to look up the value and, hey, last time I needed that number was about 40 years ago, and I’ve slept since then!)

  • Sarah,

    I think your hair is lovely (and I have a bit of envy – my hair is far too curly to have it that long). However, for safety’s sake, I really think you should do something to “tie it back” when you’re soldering or working with a soldering iron.


  • I agree that it’s a neon lamp. Trace the circuit, though: as with an LED, there should be a “limiting resistor” (also known as a “ballast resistor”) in series with it. If the lamp is the cause of the problem, the resistor is probably blown too. BTW, the neon lamp requires in the neighborhood of 70 V to “fire”, so likely is in parallel with the heating element. Neons will work on DC, but since they can also work directly on AC, they are usually connected to the AC line (though a ballast resistor). I would be inclined to open the control box back up, and after tracking down the ballast resistor and checking it with the controller not plugged into the wall, use a multimeter in AC Volts, probably 200 V range, to see if there’s voltage across the neon lamp, or across the ballast resistor (indicating current is getting through) with the thing plugged in and turned on.

    As for life span, IIRC, they quoted “50,000 hours”, though in reality, the only thing that really kills a neon lamp is “abuse”. When they go bad due to usage, they often do so slowly, starting to “flicker” in the last few thousand hours.

    Oh, yes: Back in the 60s, we had an electric blanket that had quit working, but my mother, being very thrifty, kept it and we used it as a non-electric blanket.

  • Thank you! Now I need to work it into my budget…

No public wish lists :(