Repaired Harbor Freight digital caliper

On Nov 22, 9:21=A0pm, "DoN. Nichols" <BPdnichol...@d-and-d.com> wrote:
> On 2011-11-22, dagmargoodb...@yahoo.com <dagmargoodb...@yahoo.com> wrote:

> > I saw a solar-powered Mitutoyo at a flea market and was intrigued, but
> > resisted. =A0Something 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.
>
> =A0 =A0 =A0 =A0 I've seen them only new, and decided that in my shop cond=
itions,
> they would not work very well. :-)
>
> > OTOH, I paid $10 for most of my HF calipers. =A0Those you can take
> > chances with. =A0Using 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 ;-).
>
> =A0 =A0 =A0 =A0 O.K. =A0Do you know the maximum voltage that the solar pa=
nel is
> likely to produce? =A0And the voltage drop on the LED? =A0I know that
> silicon diodes are typically between 600 mV and 750 mV. =A0Also, any clue=
s
> as to the maximum voltage that the calipers can tolerate long term?

The max. solar panel voltage doesn't matter--the LED regulator clamps
the solar panel voltage, taking care of that.

Here's a sketch:

         D1
      .--|>|--+-----+----> (+) to caliper
    + |       |     |
  .------.  + |     |
  |      |   ---   ---
  | ---- |   ---   \ / ~~>
  |      |  C1|    ---
  | ---- |    |     | LED (red)
  |      |    |     |
  '------'    |     |
   - | PV     |     |
     '--------+-----+---> (-) to caliper


 C1 - A capacitor to power the caliper during momentary outages.
Optionally a super-cap., e.g. http://www.goldmine-elec-products.com/prodinf=
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 - http://www.goldmine-elec-products.com/prodinfo.asp?number=3DG17448,
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. ;-)

--
Cheers,
James Arthur

dagmargoodboat@yahoo.com wrote:
...
> 
>          D1
>       .--|>|--+-----+----> (+) to caliper
>     + |       |     |
>   .------.  + |     |
>   |      |   ---   ---
>   | ---- |   ---   \ / ~~>
>   |      |  C1|    ---
>   | ---- |    |     | LED (red)
>   |      |    |     |
>   '------'    |     |
>    - | PV     |     |
>      '--------+-----+---> (-) to caliper
> 
...

Doncha' need a current limiter on the LED?

Bob

On 11/23/2011 2:05 PM, Bob Engelhardt wrote:
> dagmargoodboat@yahoo.com wrote:
> ...
>>
>> D1
>> .--|>|--+-----+----> (+) to caliper
>> + | | |
>> .------. + | |
>> | | --- ---
>> | ---- | --- \ / ~~>
>> | | C1| ---
>> | ---- | | | LED (red)
>> | | | |
>> '------' | |
>> - | PV | |
>> '--------+-----+---> (-) to caliper
>>
> ...
>
> Doncha' need a current limiter on the LED?
>
> Bob

Not if the PV cell's rated SC current is less than the max LED current 
rating.

Bob Engelhardt wrote:
> dagmargoodboat@yahoo.com wrote:
> ...
>>
>> D1
>> .--|>|--+-----+----> (+) to caliper
>> + | | |
>> .------. + | |
>> | | --- ---
>> | ---- | --- \ / ~~>
>> | | C1| ---
>> | ---- | | | LED (red)
>> | | | |
>> '------' | |
>> - | PV | |
>> '--------+-----+---> (-) to caliper
>>
> ...
>
> Doncha' need a current limiter on the LED?

Nup.  It's a 'shunt regulator'.
http://en.wikipedia.org/wiki/Linear_regulator#Simple_zener_regulator

--Winston

dagmargoodboat@yahoo.com wrote:

(...)

> I saw a solar-powered Mitutoyo at a flea market and was intrigued, but
> resisted.

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.

--Winston

On Nov 23, 3:05=A0pm, Bob Engelhardt <bobengelha...@comcast.net> wrote:
> dagmargoodb...@yahoo.com wrote:
>
> ...
>
> > =A0 =A0 =A0 =A0 =A0D1
> > =A0 =A0 =A0 .--|>|--+-----+----> (+) to caliper
> > =A0 =A0 + | =A0 =A0 =A0 | =A0 =A0 |
> > =A0 .------. =A0+ | =A0 =A0 |
> > =A0 | =A0 =A0 =A0| =A0 --- =A0 ---
> > =A0 | ---- | =A0 --- =A0 \ / ~~>
> > =A0 | =A0 =A0 =A0| =A0C1| =A0 =A0---
> > =A0 | ---- | =A0 =A0| =A0 =A0 | LED (red)
> > =A0 | =A0 =A0 =A0| =A0 =A0| =A0 =A0 |
> > =A0 '------' =A0 =A0| =A0 =A0 |
> > =A0 =A0- | PV =A0 =A0 | =A0 =A0 |
> > =A0 =A0 =A0'--------+-----+---> (-) to caliper
>
> ...
>
> Doncha' need a current limiter on the LED?
>
> Bob

Nope.  These little PV panels barely manage 1 or 2 mA even in
sunlight, 20uA under fluorescent.  The LED's good for 10x the PV's
max. output.

I dragged an old calculator panel out[*] and connected it to one of
those 0.6F super caps.  It's charging the cap 1mV/8s, with no load.

[*] this panel is 10x55mm--much larger than the one I referenced.  I
have several of the smaller ones, but they're all still working hard
in $1 Walmart calculators.


It's pretty impractical (clunky, delicate), but fun.


--
Cheers,
James Arthur

On Nov 23, 4:03=A0pm, Winston <Wins...@BigBrother.net> wrote:
> dagmargoodb...@yahoo.com wrote:
>
> (...)
>
> > I saw a solar-powered Mitutoyo at a flea market and was intrigued, but
> > resisted.
>
> Next time, advise jump on it before someone else does.
>
> I have two of those. They just keep working without
> any issues. =A0Well, except for turning off in low-light
> situations. =A0I just charge it up with the flashlight
> and it works just fine. =A0'Way better than having to
> run to the store for a $5 battery! =A0They are fine tools
> and have my highest recommendation.

Yes, but I got one of the HF's and hacked it up with a Dremel tool, to
mount to the lathe.

Can't do that with a Mitutoyo!

--
Cheers,
James Arthur

John S wrote:
> On 11/23/2011 2:05 PM, Bob Engelhardt wrote:

>> Doncha' need a current limiter on the LED?

> 
> Not if the PV cell's rated SC current is less than the max LED current 
> rating.

Isn't the capacitor's rated current MUCH more than the LED's?  Bob

Winston wrote:
> Bob Engelhardt wrote:
>> Doncha' need a current limiter on the LED?

> Nup.  It's a 'shunt regulator'.
> http://en.wikipedia.org/wiki/Linear_regulator#Simple_zener_regulator

The wiki ckt has a current-limiting resistor in series with the voltage 
source.  Not so the posted ckt.

Bob

dagmargoodboat@yahoo.com wrote:

(...)

> Yes, but I got one of the HF's and hacked it up with a Dremel tool, to
> mount to the lathe.
>
> Can't do that with a Mitutoyo!

And hold one's head up in public, that is.  :)

--Winston