It is an off switch to turn the *display* (only) back on. They sometimes make it also turn the display back off to make people feel better. :-)
The auto-turn-off time of the display is usually good enough.
Enjoy, DoN.
--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Actually -- there *are* some "solar powered" ones -- by Mitutoyo IIRC. They would probably be excellent used daily in a well-illuminated shop. In my shop, often dark for days at a time, until a project lures me there, the replaceable batteries are a better choice.
I did recently get an auto-darkening welding hood from Harbor Freight which is solar powered, and based on what I have read about them dying if not used regularly, I've put mine on a folding workstool facing out the window so it sees daylight to maintain the charge. I'll proably eventually have to perform surgery and replace the rechargeable cells in there. There is a temptation to provide a connection for an AC-powered trickle charger so I can store it more conveniently. What would be particularly nice would be an induction coupled charger like those for electric toothbrushes. Just put it on a stand and expect it to be fully charged when I come back.
If the charge is good enough to work on the first strike, it should work fine for the rest of the day, because it will be getting a charge boost from the arc -- close enough to vigorous sunlight. :-)
Enjoy, DoN.
--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
I saw a solar-powered Mitutoyo at a flea market and was intrigued, but resisted. Something about having a glass window on a machine tool close to all that hard steel just didn't sit well--it brought up memories of scratched and broken watch crystals.
OTOH, I paid $10 for most of my HF calipers. Those you can take chances with. Using the 8x25mm solar panel from a $1 calculator, a super capacitor for storage, and an LED as a regulator diode was my notion. $2 in parts, $500 labor ;-).
I fitted one to the lathe carriage--best thing I ever did. Removable. I fitted another to the tailstock ram. With it you can bore to 0.002" depth every time without even trying. Magic.
rbor
y
y
it
Sounds like a LiIon cell. If so, those can't be allowed to go dead, as you've surmised.
Still, there's no benefit to turning off the display, in this case. = Might=20 just as well have it display "OFF".
I bought a high-end headlamp from Coleman a few years ago
formatting link
oduct_id=3D2000000265# and every time I went to use it the batteries (4 AA) were dead. I = measured=20 the current draw when turned off, and it was something like 300 uA, = which=20 should have provided 8000 hours (almost one year) for the 2500 mA-hr=20 batteries. But I was getting only a few weeks before finding them = exhausted.=20 Maybe the current increased as the battery voltage dropped. I usually = used=20 rechargeable NiMH and they might have been old and tired. But, still, = there=20 is no reason for 300 uA standby current on a flashlight. Even if it had = a=20 microcontroller, a typical PIC18F2420 draws only 11 uA while running, = and=20 only 100 nanoamps in sleep mode! So, I just pop out one of the batteries =
while I'm not using it. There's no easy place to install a switch.
I measured some ordinary NiMH cells' self-discharge, 1,600mAH, @ 1.6mA IIRC. The high-capacity rechargeables are wickedly worse. I've got one set that won't hold a charge much over two weeks, no kidding, even brand-new. Self-discharge current on the order of 5-7mA.
There are low-self-discharge NiMH that hold a charge much longer, sometimes up to a year. Highly recommended. Ray-O-Vac Hybrids, Sanyo Eneloop, and Duracell has some too.
I've seen them only new, and decided that in my shop conditions, they would not work very well. :-)
O.K. Do you know the maximum voltage that the solar panel is likely to produce? And the voltage drop on the LED? I know that silicon diodes are typically between 600 mV and 750 mV. Also, any clues as to the maximum voltage that the calipers can tolerate long term?
[ ... ]
And -- they are supposedly not replaceable according to the manual. :-) (You've got to cut the package apart to get to them.) There is a web page describing how someone opened one up and set a holder for two AA cells outside the package. I'm really tempted to go for the induction charger when I finally have to dig into mine. But it is significantly less expensive than auto-darkening ones from MSC -- to the point where three HF ones match the cost of one from MSC. :-)
Enjoy, DoN.
--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
C1 - A capacitor to power the caliper during momentary outages. Optionally a super-cap., e.g.
formatting link
o.asp?number=3DG13133 (Note1: The PV will take HOURS of bright light to charge a super- cap, so you might want to precharge the cap, then let the PV just float it.) (Note2: Super-caps have significant electrical leakage. If your cap is too leaky, it'll never charge, and you'll be disappointed. I haven't measured the above-linked PAS920 to see if this is the case.)
PV -
formatting link
or, stolen from the cheapest solar-powered calculator you can find. Walmart and the dollar stores have some good candidates. LED - shunt-regulates the PV output to a safe voltage. D1 - 1n4148, prevents PV from draining a super-cap C1 when dark, possibly not needed. (Depends on PV panel's dark leakage current.)
To set the voltage you'd choose an LED with a forward voltage of, say
1.6-1.8v. Three ordinary small-signal silicon diodes in series (e.g.
1n4148) wouldn't be a bad choice either. With surface-mount parts, the ckt can be tiny.
If the voltage is too high it's not a matter of "long-term," the caliper will die instantly. I don't know what that voltage is, but I'd easily wager one of *my* $10 calipers that 2v is okay, and I'd wager one of *yours* that 2.5v might be okay too. ;-)
Next time, advise jump on it before someone else does.
I have two of those. They just keep working without any issues. Well, except for turning off in low-light situations. I just charge it up with the flashlight and it works just fine. 'Way better than having to run to the store for a $5 battery! They are fine tools and have my highest recommendation.
I meant the capacitor voltage source. Is its internal resistance a sufficient current limiter? I'm not familiar with super caps, but the common ones that I am familiar with will supply huge currents, momentarily.
Under no circumstances would the voltage across the LED (and capacitor) go above, say 1.8 V because the LED turns any additional voltage into current. In order for C1 to produce a current large enough to endanger the LED or the caliper, it would have to be allowed to charge significantly above the 'zener point' of the LED. It just cannot.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.