Swapping coins cells for capacitors for noise filtering

Here’s an interesting idea: replace a disposable coin cell battery with a capacitor in order to filter the noise from an external power supply. [David Cook] is taking advantage of the falling costs of digital calipers. He’s mounted one on his milling machine but noticed that with an external power supply the readings would sometimes reset in the middle of his work. The LR44 cell he’s replacing makes for very difficult in-place soldering so instead of permanently replacing it he built an insert that matched the form factor. The outer ring is from a piece of copper tubing and soldered to a PCB that he etched.

If [David's] name sounds familiar it’s because we featured his Happy Meal toy scavenging a while back.

[Thanks Thomas]


  1. Pete says:

    This guy has a lot of great ideas. For me though, My digital caliper batteries last for a really long time, even when I leave them on for extended periods of time.

  2. Deems says:

    Im going to have to try this. Great short article.

    @pete Whats the model of the caliper you have? Cause I’ve had the same problem as Dave.

  3. Pete says:

    @Deems these are the ones http://www.amazon.com/Mitutoyo-500-196-20-Absolute-Digimatic-Caliper/dp/B001QFAQ8E

    I think they have a solar version too but not mine.

  4. h_2_o says:

    neat idea but IMHO the author is having problems because of the caliper, i completely agree with pete. it appears as he is using a cheap harbor freight caliper. if you are using a good set of calipers you won’t have this problem. I’ve not had this problem on any of my mitutoyo, starrett, or brown and sharp calipers. Yeah they are more expensive but with calipers and precision instruments like this you get what you pay for.

    either way it is an interesting article.

  5. Charper says:

    On a similiar note I use a Mitutoyo 500-171. It gets used (on time) for probably 20 hours a month and has been working for over a year.

  6. Deems says:

    @Pete Would you recommend them? I paid about 300 for mine and they have given me hell since the day I bought them.

  7. Pete says:

    @deems, yeah, I love the ones I have. like h_2_0 says you do have to pay a little bit of money for A) accuracy and B) repeatability. But if you are saying you paid $300 for yours and they cause problems clearly price is not the only factor.

    I also do a sanity check (aka calibration) every so often.

  8. Sam says:

    This is very cool. I bought a pair of calipers after playing with a cheap pair in a physics class. I just couldn’t stand the idea of not owning a pair even though I don’t have a use for them.

  9. mrgoogfan says:

    i have a general tools 143 plastic digital caliper, and it works great. batteries last a week (continuously on) i’m not sure why someone would go to all this trouble. its not that hard to change a cell.

  10. jproach says:

    Changing cells every week (or even every few months) would be a pain in the ass and unnecessarily wasteful.

    There is a good write up on caliper power consumption and battery types here: http://www.davehylands.com/Machinist/Caliper-Batteries/. The cheap chinese ones use just as much power when “off” compared to on.

  11. Tommy says:

    @ h_2_o

    I couldn’t disagree more. Quality digital calipers are not a very good value IMHO.

    If you get what you pay for: then a pair of Starrett’s/Mitotoyo’s should be 30X as good as a pair of Cen tech’s.

    This is clearly not the case in my experience.

    If you need better accuracy than a pair of Cen Tech calipers can provide you’re either in Aerospace or you’re blaming your tools.

    $290 is a shitty substitute for a micrometer.

  12. localroger says:

    There is a simple, permanent solution to this: buy a dial or vernier caliper. It won’t need calibration, the battery will never die, and it won’t mysteriously stop working when you need it. On the down side you’ll have to pick metric or english units and use a calculator to convert. Calculators are a lot cheaper than calipers.

  13. Eric says:

    This is really elegant, but a huge amount of effort. If your power supply isn’t putting out clean enough power, crack open the case and put the capaciter in there.

  14. Zaero says:

    I have one of these crappy digital calipers, and tired of running out of batteries when I need to measure something, I added a battery socket for an AA battery. The good point is I always have some AA around… with 1.3V it works perfect.

  15. Pete says:

    The batteries themselves vary wildly in energy density too.

    I found a some cheap LR44 cells,105mAH each; a 2 pack for $0.35 or ~$0.0017/mAH. http://shop.jewelrydisplay.com/browse.cfm/4,2587.html

    And an SR44 Energizer, 200mAH for $2.17ea or ~$0.011/mAh


    About half of the energy density but nearly 1/15th of the cost too.

  16. McGuiver says:

    I have 3 sets of Mitutoyo digital calipers. I only change the batteries once a year. On my solar version, no battery needed. Cheap calipers just won’t last for longevity. I have had my Mitutoyo ones for almost 8 years, and still doing great. I only had the OD faces lapped once to fix the wear & tear. For my non digital I love my Brown & Sharp black face orange indicator ones.

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