Add auto turn-off to a cheap multimeter

in AVR, hacks by Ian | 6 comments

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.

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Comments

  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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