Nuclear Fusion

Checkout our caliper battery hack and a new class on creating basic schematics.

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We're teaching a class on Napking Schematics at the beginning of January. We won't be demonstrating Nuclear Fusion quite like that shown above, but we will be helping people learn the basics. This class is ideal for those who have an idea but are not quite familiar enough with available 'widgets' to be able to actually build their project.
Check my new caliper battery!

I have had the same set of calipers for a couple years now. After awhile the screen started to blink. I couldn't be sure, but I figured this meant the battery was running low. Who reads the manual anyway? It became obvious once the display cut out completely. Why does this always happens when you desperately need to measure something in a hurry?

Popping the small cover off showed a small coin cell battery. Foolishly, I assumed all coin cell batteries were the same 3V output. So I attached a larger CR2032 3V battery, assuming it would simply last longer. The unit turned on but the display was completely black - all segments where on. Hmm.

Probing around google, I discovered Dave Hylands' great page on Caliper Battery Life. It turns out these calipers are quite the battery hog. And, they use 1.5V batteries, not 3V batteries. Ooops.

I decided to create a voltage divider with a couple resistors to take the 3V of the CR2032, cut it in half, and run that 1.5V into the coil cell holder on the caliper. Digging around my tools, I came across the box of AA batteries for the Simon boards. Of course! A fresh AA battery starts at ~1.6V, but I don't really care - anything is better than having to order a silly LR44 over the internet.

I am lucky. Hooking up the 3V CR2032 Coin cell did not ruin my digital calipers. Attaching a 1.5V AA battery with double stick tape, plus two power leads soldered directly to battery and holder inside the caliper, I have a happy, non-blinking caliper readout!

Comments 22 comments

  • cyrozap / about 14 years ago / 3

    Having videos of the classes online would be nice, Going from the east coast to Colorado just to go to an electronics class isn't something I can do. It would be a great help to all of us that can't physically go to the classes.
    Just had an idea: Telepresence. I'll let you use your imaginations.

  • Andy / about 14 years ago / 3

    What are the chances of having these lectures video taped and posted online, downloadable for a reduced cost?
    also, is it still OK to say "video taped" when the media is digital?

    • Ya - working on it. Maybe skype video, maybe online conference. Not sure yet.

  • Bergamot / about 14 years ago / 3

    Can we have a wallpaper-size image of that whiteboard?

  • oren / about 14 years ago / 3

    The voltage divider most likely wouldn't have worked anyway. You typically build voltage dividers with larger resistors so that you don't draw too much current. This is fine if you just need to change the range of a voltage that you're sampling, say with an ADC, since the ADC input is usually a FET that doesn't really draw any current.
    But the whole point of a battery is to have a SMALL series resistance so that you can use it as a power supply, i.e. the voltage stays relatively stable no matter how much current you draw from it. Adding a voltage divider to a battery changes the series resistance from a few ohms to several kilohms (R1 || R2). This means that the voltage will quickly drop to near zero whenever you draw a non-negligible current from the divider tap.
    You could use smaller resistors so that the voltage drop is smaller, but then your divider will be taking a battery voltage to ground through a small resistance, and your battery will be depleted even faster.

  • R0B0T1CS / about 14 years ago / 2

    Ha, been there.
    Next time you find yourself at a job fair/ conference/ fest avoiding collecting a bag full of free toys think ?Yes, I do want a couple calculators and LED key chains. I?ll keep them for my calipers or my Mickey Mouse wrist watch?.
    For a few years I've been keeping a few 1.5v? batt?s taped inside my caliper case. Most are too small, so I smash them in there with some small plastic part. I think it?s a small wheel hub from solarbotics.

  • Chris Osborn / about 14 years ago / 2

    I have several of those kinds of digital calipers. They do not turn off! The off button only turns off the LCD, not the whole thing. The electronics stay alive constantly driving the external "serial" interface. I now always remove the battery whenever I put them away.

  • signal7 / about 14 years ago / 2

    lol. That's what I love about my vernier calipers. Easy to read and no batteries.
    I'd have to check the exact battery number, but there is a 1.5 volt version of the CR2032 that's fairly common also. Shouldn't need to order them over the internet unless you want a lot of them for some purpose....

  • Robban / about 14 years ago / 2

    Cyrozap: Going from the east coast to Colorado just to go to an electronics class isn't something I can do.
    Try flying across the Atlantic :D
    Also, I can't believe I never bothered to check the voltage my calipers use. I ran out of juice a few weeks ago and just didn't want to pay the inflated price for a new battery. Oh well, soldered and sorted now, thanks!

  • gregory / about 14 years ago / 2

    Yeah, the voltage divider is not the right tool for the job. When the caliper is off, the battery would be draining. When the caliper is on, the voltage divider equation would change.

  • Bushman / about 14 years ago / 2

    Here is a tip.
    If you need coin cells in a pinch and can't wait to buy em cheap from china: Just go to the store and buy a cheap device that uses them.
    Yeah, buy a $1 LED key chain and get $5 worth of coin cells, plus a crappy LED key chain.

  • Jassper / about 14 years ago / 2

    I think I would have just got the right battery for the job, ;)
    As for the Voltage divider, it would work. You would just need to calculate so R2 parraled with the Load resistance matched R1 of the divider.

  • Calif / about 14 years ago / 1

    Don't solder rechargeable batteries. Get a coin cell. We pay rent by the square inch in Calif* & can't afford the space for a AA.

  • PhilipH / about 14 years ago / 1

    Hi everyone,
    I have the same calipers and I have the same problem. The AA battery is a great idea but for me it would get in the way of certain measurements I take. I have not hacked these calipers yet. I was wondering if the battery rails are brought out with the data signals under the cover above the battery? If they are then it would be advantageous for me to attach an external power supply, or I could just solder to the battery holder, DUHHH! Anyway, couple of wires few feet long would work out better for me then a battery on the back of the calipers, just an idea.

  • scicior / about 14 years ago / 1

    In desperation, I have been known to "charge" a small coin cell. Yes, I know you are not suppose to, and it is potentially dangerous, but quite often it will make your calipers (or calculator, or stop watch) work for a few more minutes till you can finish what you need to do. I have never had any problems except for the time I burned my finger charging a 1.5V cell using a car battery...
    Another thing I have done, when I needed a set of A76 cells for my HP11C calculator, and only had some smaller cells, I put in a 6-32 nut to take up the space.
    Hmm, thinking about it, I wonder if I was really charging up the cell, or just heating it. Heating the cell will cause the chemical reaction to happen faster, lowering it's impedance, allowing you to wring out the last few breaths of life.
    - Steven Ciciora

  • Jassper / about 14 years ago / 1

    Of course you could have also used 2 diodes in line to get a 1.4volt drop on the 3 volt batt.
    Another trick is to peel open an A23 12v battery, you get 8 button cells for the price of 1!

  • Scienkoptic / about 14 years ago / 1

    I own the exact same caliper and the battery went dead shortly after I bought it. I ended up opening a 12V cigarette lighter battery and taking the cells out of it to use in the caliper. I had to bend the battery tabs to get them to contact the smaller cells, but so far it's working fine.

  • derb / about 14 years ago / 1

    Ha..I did the same thing with my old mp3 player except went from AAA to AA to get more life; plus I had a box full of AA's and no AAA's at the time

    • clever / about 12 years ago / 1

      i did even more with my mp3 player
      4 D's wired up, and it took 2 AAA to begin with

  • Those calipers make me think: "Heat shrink!" We should carry some large diameter heat shrink tubing for a quick enclosure. Make it clear for projects with visual indicators.

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