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Add auto turn-off to a cheap multimeter

Posted on Thursday, July 28th, 2011 in AVR, hacks by Ian

Florin was tired of wasting batteries every time he forgot to turn off his multimeter. He hacked together an auto-shutdown:

I bought this multimeter(Minipa ET-870C) a while ago for $17, great value. I got it because its nice to have around multiple meters for when you wanna measure both input and output voltage/current. I believe it was advertised to have an auto-off feature for 15 mins but it didn’t. This eventually lead to many drained batteries because I often forgot to turn it off after using it. So during a boring weekend when the weather outside was bad I decided to add this nice feature to the meter. I knew it had to be a small circuit to be able to fit inside the multimeter so I picked the tiny25 the smallest micro I had around.

This entry was posted on Thursday, July 28th, 2011 at 1:30 pm and is filed under AVR, hacks. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

6 Responses to “Add auto turn-off to a cheap multimeter”

  1. SQKYbeaver says:

    fantastic idea, my meters have the auto shutoff built in, but i can’t disable it.

  2. rsdio says:

    This sounds like another excellent candidate for a 555 timer circuit. My Honda has a super-555 chip-based auto-shutoff for the rear defroster circuit, so I assume that an auto-shutoff for a multimeter would also be workable.

    Nothing wrong with using a tiny25, but a 555 timer would work without programming.

  3. bill hill says:

    Hi guys,
    I have a Extech 410 multi-meter that has the auto-off feature but it can’t be disabled like some of the higher priced one’s. It will shut off after 15 mintues whether your using it or not, what a pain in the a**. Anyone know of a hack that will let me go onto its circuit board and cut a trace or something that will let me disable this feature? Thanks!

  4. bill hill says:

    Anyone have any ideas on how to do this?

    • rsdio says:

      It seems like you would need to start by figuring out how the auto-off works. It’s difficult to know how to defeat something if you don’t know how it works. Once it turns off, there has to be a way to turn it back on, so perhaps you could build a circuit to detect the auto-off and then have it do whatever it takes to turn it back on. Still, that might blank out an important measurement.

      • Campbell says:

        You could cut the trace to the ‘off’ switch and add your ow so it wouldn’t turn off. (That might work, but probably won’t!)

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