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dp
07-22-2009, 12:34 AM
Was blundering through some Google searches for an entirely different topic when I stumbled on to this gem: http://www.robotroom.com/CaliperCapacitor.html

I hate that all my digital stuff is packed away waiting for somebody to discover them in the crawlspace of my attic in the year 2075 because I got fed up feeding them batteries endlessly. I might have to find time to reproduce this fellow's work. The rest of his site is entertaining, too.

And yes, I am deliberately packing stuff away to be found as a surprise someday by some curious young attic crawler of the future!

tattoomike68
07-22-2009, 12:40 AM
LOL LOL LOL oh man this is a great thread. :)

J Tiers
07-22-2009, 12:51 AM
Now, if that guy had found a 'supercapacitor" that would fit a sensible sized capacity in the coin cell form factor, he'd have something.

With a unit having an external power supply capability, it could be possible to charge the thing up in as little as a few seconds and use it for an hour or two at least. That would beat batteries for many folks, you could even charge it from a "D" cell, potentially, as many of those cells are low voltage (a few are higher, but may not be used in any calipers).

I've used some calipers (they were 24" digitals) that ate a battery set in about two weeks. That got expensive in a hurry, not to mention the hassle and annoyance. You don't need 24" calipers every day, but when you do, you want them to work. IIRC, you had to use a small screwdriver to replace the batteries..... the cover was held down. That was 15 or 20 years ago, probably things are better now.

Unfortunately, the little tantalum cap he has in there is too small to work on a charge for more than a few seconds, most likely.

But, hey, what's not to like about a caliper tied down by a wire to a 'wall wart" power supply? :rolleyes:

dp
07-22-2009, 01:00 AM
Right - it was toward uber capacitance that I intended to go. His system is fine as intended, but I think it may be possible to flash charge ultra-high capacity devices to achieve the goal: to get through a day of flinging hot blue curls of expensive metal into my socks without suffering a dead battery in my digital metrology collection, or if I do, to recover with dignity and grace. I think his cable goes to the DRO, ackshually, or at least could.

J Tiers
07-22-2009, 01:05 AM
I think his cable goes to the DRO, ackshually, or at least could.

Or an SPC data collector unit. Which I guess includes power.

Forrest Addy
07-22-2009, 01:35 AM
I have two mitutoyo 6 digimatic calibers. Great tool. Accurate as hell. Never fails. The battery lasts literally for years. Not so with the cheapos. I got an impulse bought chinese digimatic knock-off caliper I bought at HF and it needs new batteries every few months.

Capacitor to bridge abattery change? Maybe on my cell phine where I have a zillion numbers etc but a digital caliper. Well, OK, why not.

dp
07-22-2009, 01:48 AM
I have two mitutoyo 6 digimatic calibers. Great tool. Accurate as hell. Never fails. The battery lasts literally for years. Not so with the cheapos. I got an impulse bought chinese digimatic knock-off caliper I bought at HF and it needs new batteries every few months.

Exactly - that is the problem to attempt to cure. To give life to cheap knock-off digital intruments. And perhaps deny some future dumpster diver a bit of cast off treasure :)

I can hear the lab reports now: "Alive.. It's alive... It's ALIVE!!"

http://www.youtube.com/watch?v=bPmVhyHBRAM

Paul Alciatore
07-22-2009, 01:48 AM
Methinks he went to a lot of un-necessary trouble. I would improvise a connector for the built-in data socket from a piece of PC board and etch a place for the capacitor on that same board. Having the capacitor an extra 0.75 " away from the battery compartment would not greatly change it's noise filtering ability and the whole thing would be a LOT easier to make. The exposed portion of the board could be insulated with a piece of 1/2" or 3/4" HST (heat shrink tubing). And it would still be possible to go back to battery operation.

Actually, I would recommend two capacitors in parallel; an electrolitic (about 100uF or more @ 5Volts) AND a disk ceramic (0.1 or 0.01uF @ 25Volts. Electrolitics have a higher impedance at high frequencies so they are not so good for filtering short (high frequency) pulses. The disc ceramic takes over this responsibility while the electrolitic handles things like 60/120 Hertz power line noise. This configuration is very common in electronic power supplies.

dp
07-22-2009, 01:54 AM
Methinks he went to a lot of un-necessary trouble.

His solution was for a simple problem - get rid of the battery. Getting rid of the battery is easy but leaves behind a problem. Electrical noise. He removed that with his capacitor. I'm betting he's not a card carrying EE so his solution worked but would not please a real card carrying EE. Hence this discussion. But none the less he's one happy camper because he kept his problem set small and solved it. I've expanded just a bit on his problem set by wanting to rid m'self of the batteries and the damn cable except for a jolt during charging. I need to dig into it to see if it is worth denying some poor geek in 2075 his trove in my attic.

As a sidebar, to hijack my own thread, what interesting bits o' stuff might any of you mischievously stuff into your attic for some young dumpsternaut to find? It's a bit like a time vault where you pass on to the future the cunning and wit of our generation.

John Stevenson
07-22-2009, 04:46 AM
Dennis,
One house we moved into had a rolled up photo in the attic.
It was one of those long college photo's with the whole lot on.

This one was from Rugby school, a quite top level paid for school in the UK, most pupils from here go on to Oxford and Cambridge

The brilliant thing about these is that there is always someone on there who looks like you at a younger age so I worked the year out and it was about 3 years out for me to have attended but the closest year would have been the first year.

Sure enough some Herbert on the bottom row looked just like me.
I framed it and stuck it up in the office, people used to walk in and say "Didn't know you went to Rugby School, which one are you ?
Just used to say bottom row middle and they would find you and say yes you haven't changed much.

Good for a hoot..................

beanbag
07-22-2009, 05:19 AM
Digital calipers have data ports?!?!?
[pops cover off my caliper]
WHOAAAAAAAA!
I feel like I just discovered something awesome in my attic, like a lady's magazine from the early 80's.

Your Old Dog
07-22-2009, 10:36 AM
I took a small block of acrylic and drilled it the size of a AA battery and used some super fine hook up wire to power the caliper on my mill. So far it's lasted thru the winter and still doing well. The SR44s wouldn't last but a few weeks in the shop that is not heated around the clock.

saltmine
07-22-2009, 11:07 AM
I can attest that the batteries seem to last forever in Mitutoyo calipers. I have been using mine in the shop since I retired (3 years ago) and have yet to need a battery replacement. HF knock-offs, you have to replace the battery every time you turn around.

Funny thing.... I've absent mindedly left my mitutoyo on for days at a time, and the battery still hasn't failed.

Paul Alciatore
07-22-2009, 01:13 PM
His solution was for a simple problem - get rid of the battery. Getting rid of the battery is easy but leaves behind a problem. Electrical noise. He removed that with his capacitor. I'm betting he's not a card carrying EE so his solution worked but would not please a real card carrying EE. Hence this discussion. But none the less he's one happy camper because he kept his problem set small and solved it. I've expanded just a bit on his problem set by wanting to rid m'self of the batteries and the damn cable except for a jolt during charging. I need to dig into it to see if it is worth denying some poor geek in 2075 his trove in my attic.

..........

His solution was very complicated just to use an external battery or AC adaptor at the other end of a cable. I just suggested a way to do the same thing that would be a lot easier and faster to implement. The capacitor(s) would still be at the caliper. I enjoy machining, but I also like to work efficiently.

My idea would also work for using one of the ultra high value capacitors as a rechargable battery. Find one that would mount on the back of the caliper's slide and just use the connector to bring power into the device. A couple of exposed contacts on the PC board used for the connector would also provide a charging connection. I have several Chinese digitals and I may try this.

Oh, and I am not an EE. My degree is in physics. I did have an IEEE card once and am a long time member of the SBE. But my suggestion is based on the easier (lazy) way to do things in a home or small shop, not any real problems with the results. Actually, for a commercial solution, his way may be better.

Forrest Addy
07-22-2009, 01:27 PM
Maybe a nano tokamak.

dp
07-22-2009, 10:03 PM
His solution was very complicated just to use an external battery or AC adaptor at the other end of a cable. I just suggested a way to do the same thing that would be a lot easier and faster to implement. The capacitor(s) would still be at the caliper. I enjoy machining, but I also like to work efficiently.

I still think you're missing what his goal is. It is finally to not have to buy batteries. It is hooked to his machine so it's got power when ever the DRO is used. Doesn't need the battery which, BTW, will run down and need replacing if left in the device when the DRO is shut down. He now has an electrically clean battery-free digital scale. And no battery bills. I'm not a physics major and I didn't even get a good night's sleep, but I know I hate mucking with batteries on my digital devices which is why they're stashed in the attic.

Paul Alciatore
07-23-2009, 01:09 AM
Denis,

I read the other pages referred to and I think I totally understand his purpose. He is using an external power source which is located at a distance from the caliper and he got some noise due to the length and location of the cable between that power source and the caliper. He also found that a filter capacitor at the caliper would eliminate that noise. Nothing could be clearer.

My suggestion was that it would be a lot easier and faster to locate the capacitor just outside of the caliper, on the connector instead of inside the caliper in place of the battery. The distance involved in this change would be about 3/4" and I doubt that that would allow any electrical noise to get into the system.

In my second post, I also suggested that the same technique could be used to eliminate the battery in favor of a super capacitor that would hold enough charge to allow the caliper to be used with no cord on it. And with NO BATTERY. But that capacitor would need recharging as it would run down. The up side is that it would probably have a longer life than a rechargable battery and you could recharge it a lot faster. This does diverge from his original idea, but I thought it was worth mentioning.

dp
07-23-2009, 01:21 AM
In my second post, I also suggested that the same technique could be used to eliminate the battery in favor of a super capacitor that would hold enough charge to allow the caliper to be used with no cord on it. And with NO BATTERY. But that capacitor would need recharging as it would run down. The up side is that it would probably have a longer life than a rechargable battery and you could recharge it a lot faster. This does diverge from his original idea, but I thought it was worth mentioning.

Diverges from his, for sure, but falls right in line with mine. I don't mind having a charging station for super cap powered gages - I just don't want to buy anymore batteries. I've not yet had a chance to explore the form factor of those devices to see if really small ones are available. They need power the device for less than 2 minutes for the typical operation I do, so a drop-in charging station would be fine. And far preferable to going off line with it because the damn battery died and I've used my last spare :)

As for stuffing the cap in the device - it does clamp noise that may be induced on the feed line at the closest possible point to the circuitry, is inside so is not unsightly and amateurish looking, and it likely satisfied his inner machinist to have whipped up a handful of them.

Frank Ford
07-23-2009, 02:04 AM
Should you care for a more serious discussion about electronic calipers and battery life, check out:

http://www.fliptronics.com/tip0006.html

dp
07-23-2009, 02:30 AM
Should you care for a more serious discussion about electronic calipers and battery life, check out:

http://www.fliptronics.com/tip0006.html

That was the site that convinced me to pack them up. That and the realization that I was rummaging through all my gages like a heavy smoker looking for a butt when my last good battery died. They may get a second life if this idea bears fruit, if not, back into the attic they go.

Rich Carlstedt
07-23-2009, 02:34 AM
The early Starritt Models has a reputation for short life.
The reason is they never shut off.
I fixed that with a plastic "isolator" that slides between the batteries and the bottom contactor whenever I return the caliper to its case
The only problem with this method, is when you slip out the pastic strip, the calipers need to be re-zeroed, which is something we should do anyway to keep things right
The sketch is self-explanitory
Rich
PS The plastic stock is "Shim" material from MSC

Notice the blank readout when the shim is installed


http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/P5270005.jpg
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/P5270007.jpg
http://i273.photobucket.com/albums/jj220/StationarySteam/Shop%20Tools/P5270008-1.jpg

JRouche
07-23-2009, 03:37 AM
I gotta say. I have the mitutoyo cal too and really, the thing just keeps on going with the original batt. Dunno if its cause it shuts off automatically, cause it seems to stay on for an entire project. And Ill look at it sitting there and want to shut it off to conserve, but I cant turn it off. But it has had the same batt in there for prolly five years now, still working..

Then I have some less expensive cals and I can turn them off. So I do, what I see the display on, and Im frugal, I hate to see an electrical device on when no one is using it. Ask my wife LOL So I do turn the cheapy cals off when Im not actually using it. But sure as not, they eat up a lil disc of batt.

I mostly use the mitutoyo. So it gets alot of use. When will the batt die? Who knows... I love the lil caliper...... JR

JMS6449
07-23-2009, 08:18 AM
Have a Fowler, auto-shutoff, battery is over 10 months old and I use it every day. Also have an old (late 80's) Mitutoyo, battery last forever, if you shut it off.

loose nut
07-23-2009, 12:00 PM
When my cheapo calipers are turned off they lose there memory and have to be zeroed when turned back on, does that mean the shut right off. The batteries last a long time.

dp
07-23-2009, 12:05 PM
When my cheapo calipers are turned off they lose there memory and have to be zeroed when turned back on, does that mean the shut right off. The batteries last a long time.

Could be - none of the ones I have shut off completely and the batteries go flat in less than 60 days. While the batteries are healthy they are accurate, smooth, and repeatable. But I have no doubt I've already spent more on batteries than I have for the instruments.

Peter.
07-23-2009, 04:32 PM
I bought a cheapy set that had auto-off and never had any battery problems. I left them behind in a workshop and haven't been able to replace them with another auto-off set. I just keep swapping the batteries when they have been flashing some time. My wife gets the batteres in pairs at the local superstore and when I have one left she gets me another pair.