Repaired Harbor Freight digital caliper

On Nov 25, 12:46 am, Jeff Liebermann <je...@cruzio.com> wrote:

On Thu, 24 Nov 2011 18:13:15 -0800 (PST), dagmargoodb...@yahoo.com
wrote:

I found this, which calculates and measures caliper battery life:
http://www.davehylands.com/Machinist/Caliper-Batteries/

Yes, good site. I linked to it earlier in this thread.

Small, cheap and simple are the main factors here.  The r.c.m. guys
aren't going to be building switching regulators, and switching
regulators generally aren't more efficient at these power levels
anyhow--their quiescent current draw's too high.

True.  However, switching regulators usually have some manner of load
shedding when the supply voltage is insufficient.  Below that
threshold, the current drain is usually in nanoamps.

(I've made a study of designing microwatt switchers, from scratch.
It's possible, but wholly inappropriate here.)

You're ahead of me.  I've never designed anything in that low power
class.  Different world.  Can you point me to a suitable (or close to
suitable) regulator chip?

There aren't any ICs with low enough Iq, at least not that I know of.
I used discrete transistors.

Not so fast...  The advantage of the thin-film PV panels is that
(appropriate) panels excel at producing power even in dim light.
Polycrystalline silicon panels don't.
The array I suggested for experimentation is thin-film for that
reason--so it can work in indoor light levels.

Decisions, decisions, and more decisions.  Polycrystaline has a cost
advantage and is more efficient than single layer thin-film.  Well, if
I wanted to go cheap, I would use amorphous cells and mold them into
the plastic case.  For small solar cells, the cost of monocrystaline
isn't all that much more (i.e. most of the cost is in packaging and
handling) but won't work well with indoor lighting.  So, I guess
thin-film is the least disgusting.
http://en.wikipedia.org/wiki/Solar_powered_calculator
   "Solar calculators may not work well in indoor
   conditions under ambient lighting as sufficient lighting
   is not available."

You can scavenge a PV from a cheap solar calculator, as low as $1. I
also linked to a part from Goldmine-elec.com.

Polycrystalline cells put out lots more in bright light, but AFAIK,
all solar calculators (and calipers, for that matter), use the
amorphous (thin-film) cells for the low-light performance. Cost might
also be a factor.

The next question is for how long will it run?  Assuming the calipers
can handle 3.0VDC without damage, how long will a junk 100UF
electrolytic cap run the calipers?

a) How long will it run?  Not nearly long enough, and b) 3.0VDC is
waayyy too risky for my blood.  20uA will discharge 100uF from 2.0V to
1.35V in 3.25 seconds.

I used 1000uF elsewhere in my calcs, but slipped here and used 100uF
instead.  Sorry.

I think you might be a bit too conservative.  5ua leakage is high.
Most of the spec sheets I've skimmed show 1-2ua for a typical 1F 5.5V
super-cap.

Of the setup I suggested, the most marginal part is the itty bitty PV
panel (its output is on the low side).  Dark leakage on my much-larger
10x55mm calculator panel is about 8uA @ 1.7V bias.

The alternative is to lose approximately 0.3V in a series Schottky
diode.  That's about 20% of the power budget, which is probably too
much.

I believe the panels put out a high enough overvoltage that the diode
loss doesn't matter--it's only going to get wasted in the LED shunt
regulators any how. I'll check.

MEASUREMENTS
Panel: 4-section 10x50mm panel, from a (retired) TI calculator:

Lighting 1: 1.8V (open), 18.5uA (short-circuit)
Lighting 2: 2.5V (open), 300uA (short-circuit)

[1] Modest indoor light (indirect sunlight, filtering through blinds,
measured from the ceiling bounce).
[2] 2' from 20W halogen bulb.

So, a 1n4148 drops too much for comfort. A BAT54 drops about 150mV
forward at these currents, and leaks a fraction of a uA at these
temperatures and reverse biases. Or, you could omit the diode and
just let the thing power down in the shade.

The supercap works wonderfully well.  Charge 0.6F to 1.8V, and you've
got 4 hours' runtime until you reach the 1.35V battery-low display-
starts-blinking level. (Assuming 20uA total draw, to allow for some
leakage.)

Ok.  You've sold me.  I was trying to see what could be done with
commodity electrolytic caps.  Also, super-caps fail to appreciate high
humidity, which may become a problem.



http://www.kpsec.freeuk.com/capacit.htm
From 1.37V is roughly 50% of full 3.0VDC charge.  That's about 80% of
1RC time constant.  1RC is:
   0.8 * 100K * 1000uF = 80 seconds
That's probably enough to make a few measurements.  Any longer and a
super-cap will probably be needed.  Picking 50% of full charge out of
the hat is rather convenient, as it makes the time to charge from zero
to the dropout point the same 80 seconds (yes, I'm lazy).  Whether the
user really wants to wait 1.5 minutes under a desk lamp for the
calipers to be usable is dubious.  Of course, a longer run time, means
a longer charge time.  For example, a 1F 5V 1ua leakage super-cap,
will run the calipers for 80,000 seconds, but will also take 80,000
seconds to charge.

Not 80,000s.  Expose the PV to sunlight (or directly to a lamp), and
it'll charge (initially) >50x faster.  You'd only have to do that
once.  Indoors, the PV would keep it topped off, that's the idea.

Yep.  However, I screwed up.  The discharge load is:
   1.5VDC / 15uA = 100K ohms
However, the charging ESR is much less.
   3.0VDC / 2ma = 1.5K
It will certainly be higher a lower illumination levels.  Checking my
junk cell under random room lighting conditions, and again scaling for
size, I get:
   0.333 * 0.55v / 0.02mA = 9.2K
I don't have a small thin film panel to test.  (I have 90watt panel,
but that's a bit much for scaling to caliper size).

Alternatively, an electrolytic works, but gives a caliper that quickly
quits if you accidentally shadow it.

Not if you do exactly like it's done with a calculator.  When the cell
is shaded, it runs on battery.  A silver-oxide battery holds:
   1.5v * 150 mA-Hr = 22.5 milliwatt-Hrs
and will deliver most of that before the voltage drops to unusable
levels.

The super cap will deliver (very roughly):
   1.5v * 15uA * 4Hr = 90 microwatt-Hrs

There are much smaller supercaps--0.02F--used in cellphones.  That's
another option / compromise.  Leakage should be better too.

Overview of CDE super-caps:
http://www.cde.com/catalogs/EDL.pdf
Some interesting notes on charge time and lifetime near the bottom.

In my never humble opinion, what makes more sense is to do it exactly
like the typical solar powered calculator.  They all have one or two
LR44 batteries inside.  However, the solar cell does NOT charge the
battery.  When you turn the calculator on, and there's enough light to
run from the solar cell, the battery is essentially disconnected. When
there's not enough light to run the calculator, it runs off the
battery.  No waiting to charge a capacitor from the solar cell.

That uses the PV as, basically, a battery-extender.  That's fine, but
complex--you need a micro-power switch to disconnect the battery, etc.
(A diode drops waayyy too much voltage.)  That puts it out of the
realm of a simple project that can fit into the existing caliper.

There has to be a chip in the calipers anyway to count pulses, run the
display, and deal with the push buttons.  Adding a power management
feature does not add much real estate or complexity.  However, if
you're thinking of a retrofit, I suspect something could be done with
a separate switcher chip.

If we're designing it from scratch, we just wouldn't use so darn much
power to start with. Then, a PV panel and a capacitor are all you
need.

Switcher chips just don't do well on 20uA power input.

If you're into high tech, there are various energy scavenging devices
that can also power the calipers.
http://en.wikipedia.org/wiki/Energy_harvesting
With only 22.5 microwatts required, it might be possible to power the
device with a wind up key, piezo pressure, body heat, kinetic magnetic
generator, etc.  I kinda like the idea of a wind up caliper.

Windup would be fun--steampunk.

In the late 1960's, I designed and built a paging receiver, that
produced the message output on a 1/4" wide roll of paper tape. Battery
power to the mechanics for such a portable device was impossible.  So,
I went to a wind up coil spring mechanism.  I've been somewhat of a
fan of spring power ever since.

The "real" solution is to design the caliper to draw less current in
the first place, like Mitutoyo and Starrett.  If you've done that,
solar-powering is a snap, but then, if the battery lasts years, you
don't need solar power, do you?

Agreed.  It would be like a digital watch, which typically has a 10
year battery life.  However, the solar cell is still a problem because
of the dark current (reverse leakage).  An isolating Schottky diode
can reduce that, but then the solar cell would need to be about 20%
larger to compensate for the added loss.

Another problem is that it would be no fun.  Windup calipers offer a
far more entertaining problem to solve.

Windup calipers--that's cool!

--
Cheers,
James Arthur

 

On Nov 25, 1:29 am, Jeff Liebermann <je...@cruzio.com> wrote:

On Thu, 24 Nov 2011 21:46:48 -0800, Jeff Liebermann <je...@cruzio.com
wrote:

The next question is for how long will it run?  Assuming the calipers
can handle 3.0VDC without damage, how long will a junk 100UF
electrolytic cap run the calipers?

a) How long will it run?  Not nearly long enough, and b) 3.0VDC is
waayyy too risky for my blood.  20uA will discharge 100uF from 2.0V to
1.35V in 3.25 seconds.

Trying the same calc using the super-cap formula from Pg 6 of:
http://www.cde.com/catalogs/EDL.pdf

   t = C delta V / I
   t = C[V0-(i*R)-V1] / (i+iL)
where:
    t: Back-up time (sec)
    C: Capacitance of Type EDL (Farads)
   V0: Applied voltage (Volts)
   V1: Cut-off voltage (Volts)
    i: Current during back-up (Amps)
   iL: Leakage current (Amps)
    R: Internal resistance (ohms) at 1 kHz

For this example, I'll use a 0.1F (type F) 5.5V 100 ohm cap.
The low end of the tolerance range might drop this to 0.08F.
V0 = 2.0V, V1 = 1.4V, i = 15uA, iL = 2uA

That cap is 14x10mm, pretty humungous. You don't need 5.5v, so the
'EN' type, at 7x2mm and 0.2F might be a better fit.

Plugging in:
 t = C[V0-(i*R)-V1] / (i+iL)
 t = 0.08F[2.0V-(15uA*100ohms)-1.4V]/(15uA+2uA)
 t = 2800 sec = 47 minutes.
Not bad.

I calculated the caliper as being a constant-current drain on the
super cap, then applied Q=CV. Actual current drain drops a tad with
falling Vdd, so my approximation is probably slightly conservative.

I guess the protective case that most calipers use will need a clear
plastic window to keep it charged.  Maybe another window on top of my
toolbox.

Yep. Another retro-fit possibility is to fit a supercap in the
caliper, and a lithium-AA (1.65v) in the caliper case that recharges
the supercap when not in use.

That'll last forever (about 10years on the 'AA'), runs for hours per
charge, fits the case easily, and doesn't need a PV or any fancy
circuitry. The PAS920 I linked before costs 5/$1 surplus, from
Goldmine-elec.com.


--
Cheers,
James Arthur

 

[krw@att.bizzzzzzzzzzzz]

On Fri, 25 Nov 2011 07:06:57 -0800 (PST), dagmargoodboat@yahoo.com wrote:

On Nov 25, 12:46 am, Jeff Liebermann <je...@cruzio.com> wrote:
On Thu, 24 Nov 2011 18:13:15 -0800 (PST), dagmargoodb...@yahoo.com
wrote:

I found this, which calculates and measures caliper battery life:
http://www.davehylands.com/Machinist/Caliper-Batteries/

Yes, good site. I linked to it earlier in this thread.

Small, cheap and simple are the main factors here.  The r.c.m. guys
aren't going to be building switching regulators, and switching
regulators generally aren't more efficient at these power levels
anyhow--their quiescent current draw's too high.

True.  However, switching regulators usually have some manner of load
shedding when the supply voltage is insufficient.  Below that
threshold, the current drain is usually in nanoamps.

(I've made a study of designing microwatt switchers, from scratch.
It's possible, but wholly inappropriate here.)

You're ahead of me.  I've never designed anything in that low power
class.  Different world.  Can you point me to a suitable (or close to
suitable) regulator chip?

There aren't any ICs with low enough Iq, at least not that I know of.
I used discrete transistors.

There are some pretty good ones, designed for USB applications, but I don't
thing they're quite good enough for this. The TPS6205x Iq is around 5uA to and
in shutdown less than 2uA. You're looking for something an order of magnitude
better than this?

<...>

 

On Nov 25, 5:31 pm, "k...@att.bizzzzzzzzzzzz"
<k...@att.bizzzzzzzzzzzz> wrote:

On Fri, 25 Nov 2011 07:06:57 -0800 (PST), dagmargoodb...@yahoo.com wrote:
On Nov 25, 12:46 am, Jeff Liebermann <je...@cruzio.com> wrote:
On Thu, 24 Nov 2011 18:13:15 -0800 (PST), dagmargoodb...@yahoo.com
wrote:

I found this, which calculates and measures caliper battery life:
http://www.davehylands.com/Machinist/Caliper-Batteries/

Yes, good site.  I linked to it earlier in this thread.

Small, cheap and simple are the main factors here.  The r.c.m. guys
aren't going to be building switching regulators, and switching
regulators generally aren't more efficient at these power levels
anyhow--their quiescent current draw's too high.

True.  However, switching regulators usually have some manner of load
shedding when the supply voltage is insufficient.  Below that
threshold, the current drain is usually in nanoamps.

(I've made a study of designing microwatt switchers, from scratch.
It's possible, but wholly inappropriate here.)

You're ahead of me.  I've never designed anything in that low power
class.  Different world.  Can you point me to a suitable (or close to
suitable) regulator chip?

There aren't any ICs with low enough Iq, at least not that I know of.
I used discrete transistors.

There are some pretty good ones, designed for USB applications, but I don't
thing they're quite good enough for this. The TPS6205x Iq is around 5uA to and
in shutdown less than 2uA.  You're looking for something an order of magnitude
better than this?

...

http://www.ti.com/lit/ds/symlink/tps62050.pdf

From the graph on the front page, it looks like n = ~35% @ 15uA
output. That's actually very good. Thanks.

My designs were mostly boost topology, so there may be ICs I didn't
consider (plus new ICs I haven't seen). I did some nutty stuff, like
nano-amp oscillators and micro-amp switchers that were roughly 75%
efficient.

--
Cheers,
James Arthur

 

[Jeff Liebermann]

On Fri, 25 Nov 2011 21:28:54 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Nov 25, 5:31 pm, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
(...)
http://www.ti.com/lit/ds/symlink/tps62050.pdf

From the graph on the front page, it looks like n = ~35% @ 15uA
output. That's actually very good. Thanks.

That's because of the 12uA typical quiescent current, where the chip
draws about the same current as the caliper load. For equal currents,
that's 50% maximum efficiency. The TPS62054 shows 50% efficiency at
2.7V in and 1.8V out (See Pg 8 Fig 4).

The chips do have a shutdown pin that cuts the quiescent current to
"less than 2uA". Still high, but much better.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[P E Schoen]

"Jeff Liebermann" wrote in message
news:u482d71le9hutbmkgb1hg24c3hpevbvlop@4ax.com...

That's because of the 12uA typical quiescent current, where the
chip draws about the same current as the caliper load. For equal
currents, that's 50% maximum efficiency. The TPS62054 shows
50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4).

The chips do have a shutdown pin that cuts the quiescent
current to "less than 2uA". Still high, but much better.

A step-down regulator/converter could be made from a Microchip PIC18LF14K22
(http://ww1.microchip.com/downloads/en/DeviceDoc/41365c.pdf) which has a
quiescent current of 34nA and an operating current of about 10 uA at 1.8
VDC.

And it may be even more efficient to use a low power linear regulator such
as the TPS71501 (http://www.ti.com/product/tps71501) which has 3.3 uA
quiescent current. If the input voltage is, say, 2 VDC and the output is 1.6
VDC at 12 uA, the overall efficiency is (1.6*12)/(2*15.3) or almost 63%.
Even at 3 VDC input it is 42%.

Paul

 

[krw@att.bizzzzzzzzzzzz]

On Sun, 27 Nov 2011 07:35:00 -0800 (PST), dagmargoodboat@yahoo.com wrote:

On Nov 26, 12:36 pm, Jeff Liebermann <je...@cruzio.com> wrote:
On Fri, 25 Nov 2011 21:28:54 -0800 (PST), dagmargoodb...@yahoo.com
wrote:



On Nov 25, 5:31 pm, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
(...)
http://www.ti.com/lit/ds/symlink/tps62050.pdf
From the graph on the front page, it looks like n = ~35%  @ 15uA
output.  That's actually very good.  Thanks.

That's because of the 12uA typical quiescent current, where the chip
draws about the same current as the caliper load.  For equal currents,
that's 50% maximum efficiency.  The TPS62054 shows 50% efficiency at
2.7V in and 1.8V out (See Pg 8 Fig 4).

The chips do have a shutdown pin that cuts the quiescent current to
"less than 2uA".  Still high, but much better.

Yes, but, in the caliper context, who's going to turn the switcher
off, how, and when?

When the photocell voltage output too low to power the calipers?

>See the problem?

 

On Nov 26, 12:36 pm, Jeff Liebermann <je...@cruzio.com> wrote:

On Fri, 25 Nov 2011 21:28:54 -0800 (PST), dagmargoodb...@yahoo.com
wrote:



On Nov 25, 5:31 pm, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
(...)
http://www.ti.com/lit/ds/symlink/tps62050.pdf
From the graph on the front page, it looks like n = ~35%  @ 15uA
output.  That's actually very good.  Thanks.

That's because of the 12uA typical quiescent current, where the chip
draws about the same current as the caliper load.  For equal currents,
that's 50% maximum efficiency.  The TPS62054 shows 50% efficiency at
2.7V in and 1.8V out (See Pg 8 Fig 4).

The chips do have a shutdown pin that cuts the quiescent current to
"less than 2uA".  Still high, but much better.

Yes, but, in the caliper context, who's going to turn the switcher
off, how, and when?

See the problem?

--
Cheers,
James Arthur

 

On Nov 26, 5:09 pm, "P E Schoen" <p...@pstech-inc.com> wrote:

"Jeff Liebermann"  wrote in message

news:u482d71le9hutbmkgb1hg24c3hpevbvlop@4ax.com...

That's because of the 12uA typical quiescent current, where the
chip draws about the same current as the caliper load.  For equal
currents, that's 50% maximum efficiency.  The TPS62054 shows
50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4).
The chips do have a shutdown pin that cuts the quiescent
current to "less than 2uA".  Still high, but much better.

A step-down regulator/converter could be made from a Microchip PIC18LF14K22
(http://ww1.microchip.com/downloads/en/DeviceDoc/41365c.pdf) which has a
quiescent current of 34nA and an operating current of about 10 uA at 1.8
VDC.

And it may be even more efficient to use a low power linear regulator such
as the TPS71501 (http://www.ti.com/product/tps71501) which has 3.3 uA
quiescent current. If the input voltage is, say, 2 VDC and the output is 1.6
VDC at 12 uA, the overall efficiency is (1.6*12)/(2*15.3) or almost 63%.
Even at 3 VDC input it is 42%.

Paul

The LED shunt regulator saves the 2uA, so it's simpler, cheaper, and
even more efficient.

--
Cheers,
James Arthur

 

[Jeff Liebermann]

On Sun, 27 Nov 2011 07:35:00 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Nov 26, 12:36 pm, Jeff Liebermann <je...@cruzio.com> wrote:
On Fri, 25 Nov 2011 21:28:54 -0800 (PST), dagmargoodb...@yahoo.com
wrote:



On Nov 25, 5:31 pm, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
(...)
http://www.ti.com/lit/ds/symlink/tps62050.pdf
From the graph on the front page, it looks like n = ~35%  @ 15uA
output.  That's actually very good.  Thanks.

That's because of the 12uA typical quiescent current, where the chip
draws about the same current as the caliper load.  For equal currents,
that's 50% maximum efficiency.  The TPS62054 shows 50% efficiency at
2.7V in and 1.8V out (See Pg 8 Fig 4).

The chips do have a shutdown pin that cuts the quiescent current to
"less than 2uA".  Still high, but much better.

Yes, but, in the caliper context, who's going to turn the switcher
off, how, and when?

A timer. Caliper runs for 120 seconds and then shuts off. I have a
few small battery operated devices like this that have no OFF switch.
Just punch any button, and it turns on. Wait a while, and it turns
off. My Central Tools "Storm" 3C301 cheapo electronic calipers has
this feature.
<http://www.amazon.com/Storm-6in-Digital-Caliper-Model/dp/B000VZ2ZB6>
The unintelligible owners manual proudly highlights this feature on
the cover. Apparently, previous versions did NOT turn off
automatically. Oddly, it still has an on/off push button, even though
it will turn on if the jaws are moved.

Hmmm... the catalog says that it ships with an SR44/357 silver oxide
battery. Yet, the one I purchased had alkaline LR44 batteries.
<http://www.centraltools.com/pdf/Catalog_Storm.pdf>

See the problem?

Nope.

I still think that wind up power would be more interesting.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

On Nov 27, 12:17 pm, Jeff Liebermann <je...@cruzio.com> wrote:

On Sun, 27 Nov 2011 07:35:00 -0800 (PST), dagmargoodb...@yahoo.com
wrote:



On Nov 26, 12:36 pm, Jeff Liebermann <je...@cruzio.com> wrote:
On Fri, 25 Nov 2011 21:28:54 -0800 (PST), dagmargoodb...@yahoo.com
wrote:

On Nov 25, 5:31 pm, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
(...)
http://www.ti.com/lit/ds/symlink/tps62050.pdf
From the graph on the front page, it looks like n = ~35%  @ 15uA
output.  That's actually very good.  Thanks.

That's because of the 12uA typical quiescent current, where the chip
draws about the same current as the caliper load.  For equal currents,
that's 50% maximum efficiency.  The TPS62054 shows 50% efficiency at
2.7V in and 1.8V out (See Pg 8 Fig 4).

The chips do have a shutdown pin that cuts the quiescent current to
"less than 2uA".  Still high, but much better.
Yes, but, in the caliper context, who's going to turn the switcher
off, how, and when?

A timer.  Caliper runs for 120 seconds and then shuts off.

But then the caliper forgets its "zero" every two minutes. That's
very annoying.

I have a
few small battery operated devices like this that have no OFF switch.
Just punch any button, and it turns on.  Wait a while, and it turns
off.  My Central Tools "Storm" 3C301 cheapo electronic calipers has
this feature.
http://www.amazon.com/Storm-6in-Digital-Caliper-Model/dp/B000VZ2ZB6
The unintelligible owners manual proudly highlights this feature on
the cover.  Apparently, previous versions did NOT turn off
automatically.  Oddly, it still has an on/off push button, even though
it will turn on if the jaws are moved.

Hmmm... the catalog says that it ships with an SR44/357 silver oxide
battery.  Yet, the one I purchased had alkaline LR44 batteries.
http://www.centraltools.com/pdf/Catalog_Storm.pdf

See the problem?

Nope.

The problem is that it's a much more complicated design, much more
than a metalworking hobbyist could reasonably tackle to upgrade his HF
cheapies.

If we're designing calipers from scratch, we'd just design them for
2uA total draw, not add an outboard switcher with Iq=2uA, then add a
timer to turn it off.

I still think that wind up power would be more interesting.

Yep, that's still intriguing. As a practical matter, how do you turn
spring tension into 15uA / 1.55V? A generator, an escapement, a coil
and a magnet I suppose. Time to call a watchmaker.

--
Cheers,
James Arthur

 

[Jeff Liebermann]

On Sun, 27 Nov 2011 10:45:00 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

But then the caliper forgets its "zero" every two minutes. That's
very annoying.

Mine doesn't. The initial position is apparently stored in the
circuitry. I can also set it to any position, turn it off, and it
will read the same value when turned back on. One of the benefits of
having it draw power continuously.

The problem is that it's a much more complicated design, much more
than a metalworking hobbyist could reasonably tackle to upgrade his HF
cheapies.

Retrofits are always more complicated. I tend to think in terms of
new product designs. If this were for a retrofit or modification, the
design philosphy would certainly be different.

If we're designing calipers from scratch, we'd just design them for
2uA total draw, not add an outboard switcher with Iq=2uA, then add a
timer to turn it off.

Agreed. At 2uA, it probably wouldn't need an on/off switch.

I still think that wind up power would be more interesting.

Yep, that's still intriguing. As a practical matter, how do you turn
spring tension into 15uA / 1.55V? A generator, an escapement, a coil
and a magnet I suppose. Time to call a watchmaker.

Pancake PM generator which offers the highest velocity at the edge.
Basically a magnetized disk and a stator coil. Spring loaded spool
parallel to the pancake motor and the same size. Ratchet to control
direction. Inertial clutch and some plastic gears between the spool
and the pancake motor. Much like a generator powered flashlight. Pull
on the string and the spool spins, which causes the generator to run,
charging a super-cap. If a pull string is too crude, a spiral
mainspring mechanism can be added. If the pull string and generator
are too sophisticated, a moving magnet inside a coil, that you shake
back and forth to charge the super-cap, much like in some battery-less
flashlights. Maybe a thumb wheel for spinning the pancake generator
might better. Plenty of options.

I can grind the energy budget numbers (later) if you want. There's
plenty of power available in string pull and wind up. However,
without a backup battery, the stored zero setting will be lost when
the super-cap discharges. Such is the price of entertainment value.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Winston]

Jeff Liebermann wrote:

On Sun, 27 Nov 2011 10:45:00 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

But then the caliper forgets its "zero" every two minutes. That's
very annoying.

Mine doesn't. The initial position is apparently stored in the
circuitry. I can also set it to any position, turn it off, and it
will read the same value when turned back on. One of the benefits of
having it draw power continuously.

The problem is that it's a much more complicated design, much more
than a metalworking hobbyist could reasonably tackle to upgrade his HF
cheapies.

Retrofits are always more complicated. I tend to think in terms of
new product designs. If this were for a retrofit or modification, the
design philosphy would certainly be different.

If we're designing calipers from scratch, we'd just design them for
2uA total draw, not add an outboard switcher with Iq=2uA, then add a
timer to turn it off.

Agreed. At 2uA, it probably wouldn't need an on/off switch.

I still think that wind up power would be more interesting.

Yep, that's still intriguing. As a practical matter, how do you turn
spring tension into 15uA / 1.55V? A generator, an escapement, a coil
and a magnet I suppose. Time to call a watchmaker.

Pancake PM generator which offers the highest velocity at the edge.
Basically a magnetized disk and a stator coil. Spring loaded spool
parallel to the pancake motor and the same size. Ratchet to control
direction. Inertial clutch and some plastic gears between the spool
and the pancake motor. Much like a generator powered flashlight. Pull
on the string and the spool spins, which causes the generator to run,
charging a super-cap. If a pull string is too crude, a spiral
mainspring mechanism can be added. If the pull string and generator
are too sophisticated, a moving magnet inside a coil, that you shake
back and forth to charge the super-cap, much like in some battery-less
flashlights. Maybe a thumb wheel for spinning the pancake generator
might better. Plenty of options.

How about a weighted leaf switch in series with the
cell? It could take the form of a thicker
'battery door'. The bulk bypass caps in the caliper
would hopefully maintain power during vibration
glitches and overhead measurements.

Place the caliper 'display down' and power
is removed.

--Winston<--Cheap! Quick!

 

[Jeff Liebermann]

On Sun, 27 Nov 2011 14:08:41 -0800, Winston <Winston@BigBrother.net>
wrote:

How about a weighted leaf switch in series with the
cell? It could take the form of a thicker
'battery door'. The bulk bypass caps in the caliper
would hopefully maintain power during vibration
glitches and overhead measurements.

Place the caliper 'display down' and power
is removed.

--Winston<--Cheap! Quick!

Retch. A position sensitive on/off mechanism is prone to failure if
the device is parked in an unusual position. For example, if I put it
in it's protective case, and then toss it into my toolbox face up, it
will remain on. It would also prevent me from using in the face down
position.

Please don't suggest an inertial on/off mechanism (shake to operate).
Bouncing around in my car will probably turn it on.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Winston]

Jeff Liebermann wrote:

(...)

Retch. A position sensitive on/off mechanism is prone to failure if
the device is parked in an unusual position. For example, if I put it
in it's protective case, and then toss it into my toolbox face up, it
will remain on.

Even if you stored the caliper 'face up' for a year,
it would cost you no more than if you had no
switch at all. Net net, battery life would increase
because, the caliper would be turned off for a far
longer time than it would be turned on.

It would also prevent me from using in the face down
position.

I was appalled that I can't use my blender
upside down too, until I realized that I never
have a need to do that.

Please don't suggest an inertial on/off mechanism (shake to operate).
Bouncing around in my car will probably turn it on.

If you drive your car 24/365, you have much bigger
efficiency worries than a $1.00 cell!

--Winston

 

[Jeff Liebermann]

On Sun, 27 Nov 2011 22:18:49 -0800, Winston <Winston@BigBrother.net>
wrote:

Jeff Liebermann wrote:

(...)

Retch. A position sensitive on/off mechanism is prone to failure if
the device is parked in an unusual position. For example, if I put it
in it's protective case, and then toss it into my toolbox face up, it
will remain on.

Even if you stored the caliper 'face up' for a year,
it would cost you no more than if you had no
switch at all. Net net, battery life would increase
because, the caliper would be turned off for a far
longer time than it would be turned on.

This is what happens when we lose sight of the original problem that
we're trying to solve. The problem is that the calipers have a short
battery life mostly because they don't really turn off and secondarily
because the dropout voltage is too high to use cheap alkaline
batteries. Turning the calipers off (actually in standby) for a year
won't do much, when the operating current is 14.5uA and the off
current is 13.5uA.

It would also prevent me from using in the face down
position.

I was appalled that I can't use my blender
upside down too, until I realized that I never
have a need to do that.

You need to contact a product liability attorney, and sue for damages
resulting from inverted operation. Be sure to mention that there was
no warning in the user manual about inverted operation.

I've used calipers and other measuring instruments in probably every
orientation possible. If the calipers turned off while I was making
measurements in a contortionists position, I would be rather
irritated.

Please don't suggest an inertial on/off mechanism (shake to operate).
Bouncing around in my car will probably turn it on.

If you drive your car 24/365, you have much bigger
efficiency worries than a $1.00 cell!

True. Also, if I don't drive the car at all, I get an infinitely
large gasoline mileage. Both extremes are worthless. I non-cleverly
installed a "shake to unlock" (iShakeLock) application on my iPhone
3G. The standard method of unlocking the phone requires both hands. I
figured that one handed unlocking would be better. The problem was
that it kept unlocking in my pocket. Battery life deteriorated
rapidly. So, I dumped the app.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Winston]

Jeff Liebermann wrote:

On Sun, 27 Nov 2011 22:18:49 -0800, Winston<Winston@BigBrother.net
wrote:

Jeff Liebermann wrote:

(...)

Retch. A position sensitive on/off mechanism is prone to failure if
the device is parked in an unusual position. For example, if I put it
in it's protective case, and then toss it into my toolbox face up, it
will remain on.

Even if you stored the caliper 'face up' for a year,
it would cost you no more than if you had no
switch at all. Net net, battery life would increase
because, the caliper would be turned off for a far
longer time than it would be turned on.

This is what happens when we lose sight of the original problem that
we're trying to solve. The problem is that the calipers have a short
battery life mostly because they don't really turn off and secondarily
because the dropout voltage is too high to use cheap alkaline
batteries. Turning the calipers off (actually in standby) for a year
won't do much, when the operating current is 14.5uA and the off
current is 13.5uA.

Er. Jeff?

I was talking about the open circuit represented
by a 'position' switch. Off current would be
*far* lower than 13.5 uA.

It would also prevent me from using in the face down
position.

I was appalled that I can't use my blender
upside down too, until I realized that I never
have a need to do that.

You need to contact a product liability attorney, and sue for damages
resulting from inverted operation. Be sure to mention that there was
no warning in the user manual about inverted operation.

I've used calipers and other measuring instruments in probably every
orientation possible. If the calipers turned off while I was making
measurements in a contortionists position, I would be rather
irritated.

What proportion of the time do you measure
with the display facing down?
For me it is a very tiny amount
of time. Like seconds-per-decade.

I own seven pairs of calipers, two of which are dial,
two of which are solar, two of which are very
cheap digitals and one is a vernier.
Of them, only the cheap digitals would benefit
from this conversion. I would select
the proper measuring tool for the job.

You do as well, I trust.

Please don't suggest an inertial on/off mechanism (shake to operate).
Bouncing around in my car will probably turn it on.

If you drive your car 24/365, you have much bigger
efficiency worries than a $1.00 cell!

True. Also, if I don't drive the car at all, I get an infinitely
large gasoline mileage. Both extremes are worthless.

I dunno. The 24/365 commute places an upper limit
on the amount of time that the calipers would remain
powered up. It probably would cost you say $1.20 a year
to leave them 'rightside up' in your toolbox.
I don't think of this as a huge toll, somehow.

Perspective!

I non-cleverly
installed a "shake to unlock" (iShakeLock) application on my iPhone
3G. The standard method of unlocking the phone requires both hands. I
figured that one handed unlocking would be better. The problem was
that it kept unlocking in my pocket. Battery life deteriorated
rapidly. So, I dumped the app.

You keep your iPhone next to your calipers in your pocket?

Don't the pointy 'inside' anvils smart a bit?



--Winston<--Tell me about your pocket lint.

 

On Nov 27, 5:08 pm, Winston <Wins...@BigBrother.net> wrote:

Jeff Liebermann wrote:
On Sun, 27 Nov 2011 10:45:00 -0800 (PST), dagmargoodb...@yahoo.com
wrote:

But then the caliper forgets its "zero" every two minutes.  That's
very annoying.

Mine doesn't.  The initial position is apparently stored in the
circuitry.  I can also set it to any position, turn it off, and it
will read the same value when turned back on.  One of the benefits of
having it draw power continuously.

The problem is that it's a much more complicated design, much more
than a metalworking hobbyist could reasonably tackle to upgrade his HF
cheapies.

Retrofits are always more complicated.  I tend to think in terms of
new product designs.  If this were for a retrofit or modification, the
design philosphy would certainly be different.

If we're designing calipers from scratch, we'd just design them for
2uA total draw, not add an outboard switcher with Iq=2uA, then add a
timer to turn it off.

Agreed.  At 2uA, it probably wouldn't need an on/off switch.

I still think that wind up power would be more interesting.

Yep, that's still intriguing.  As a practical matter, how do you turn
spring tension into 15uA / 1.55V?  A generator, an escapement, a coil
and a magnet I suppose.  Time to call a watchmaker.

Pancake PM generator which offers the highest velocity at the edge.
Basically a magnetized disk and a stator coil.  Spring loaded spool
parallel to the pancake motor and the same size.   Ratchet to control
direction.  Inertial clutch and some plastic gears between the spool
and the pancake motor.  Much like a generator powered flashlight. Pull
on the string and the spool spins, which causes the generator to run,
charging a super-cap.  If a pull string is too crude, a spiral
mainspring mechanism can be added.  If the pull string and generator
are too sophisticated, a moving magnet inside a coil, that you shake
back and forth to charge the super-cap, much like in some battery-less
flashlights.  Maybe a thumb wheel for spinning the pancake generator
might better.  Plenty of options.

How about a weighted leaf switch in series with the
cell?   It could take the form of a thicker
'battery door'. The bulk bypass caps in the caliper
would hopefully maintain power during vibration
glitches and overhead measurements.

Place the caliper 'display down' and power
is removed.

--Winston<--Cheap! Quick!

Decent! How about this as a retrofit to the Harbor Freight cheapies:

push a pushbutton switch, which charges a supercap when you need it,
giving an hour or so runtime per press?

Iq = 0uA.
Battery life: Same as shelf life.
Parts list: homemade switch, supercap. $0.20.

Caliper starts blinking? Press the button again to keep it going.

--
Cheers,
James Arthur

 

[Winston]

dagmargoodboat@yahoo.com wrote:

(...)

Decent! How about this as a retrofit to the Harbor Freight cheapies:

push a pushbutton switch, which charges a supercap when you need it,
giving an hour or so runtime per press?

Iq = 0uA.
Battery life: Same as shelf life.
Parts list: homemade switch, supercap. $0.20.

Caliper starts blinking? Press the button again to keep it going.

I like that! But I can reduce the BOM size.
Just a (rotary?) switch in the battery cover.

If you leave it on, you get 10 months
out of the battery. If you use the power
switch religiously, you get 'shelf life'.

* A switch handling ~40 uA does not have to
be nearly as stout as one handling 'short circuit'
current into the super cap.

* Most super caps don't tolerate high current well.

* This mod is dead simple, reversible and does not
require access to a ground connection.

--Winston

 

On Nov 28, 2:43 pm, Winston <Wins...@BigBrother.net> wrote:

dagmargoodb...@yahoo.com wrote:

(...)

Decent!  How about this as a retrofit to the Harbor Freight cheapies:

push a pushbutton switch, which charges a supercap when you need it,
giving an hour or so runtime per press?

   Iq = 0uA.
   Battery life: Same as shelf life.
   Parts list: homemade switch, supercap.  $0.20.

Caliper starts blinking?  Press the button again to keep it going.

I like that!  But I can reduce the BOM size.
Just a (rotary?) switch in the battery cover.

If you leave it on, you get 10 months
out of the battery. If you use the power
switch religiously, you get 'shelf life'.

* A switch handling ~40 uA does not have to
   be nearly as stout as one handling 'short circuit'
   current into the super cap.

Low-current switches can be a bear--the contacts oxidize. Gold fixes
that generally, IIRC.

* Most super caps don't tolerate high current well.

No problem here. The low battery voltage and high internal resistance
of these tiny cell-phone super caps limits the current nicely.

* This mod is dead simple, reversible and does not
   require access to a ground connection.

I like some sort of dead-man timer better. It could be just a low
threshold mosfet with a gate cap which you charge, and a *large*
discharge resistor(*) so it times out. That guarantees the battery-
saving feature even if you forget.

(*) (From the jellybean / junkbox standpoint, the discharge "resistor"
might be a reverse-biased rectifier's leakage.)

But yes, just adding a real switch is a huge improvement over not
having it.

A real switch also lets you hold the zero setting over night if you
want to. I sometimes do that with the lathe, if, for example, I'm in
the middle of something when it's time to turn in.

You *do* need access to the underside of the cell, since that's where
the (-) contact is. Insert a very thin piece of double-sided printed
circuit mat'l, wire a tiny slide switch to both sides of that, and
Bob's yer uncle.

That's reversible, and if you're a brute, you can even hang the switch
outboard by the wires. That way there's no modification of the
caliper needed at all.

That's good enough and simple enough that I'll put 'er on the list.
I've got maybe a dozen of these (two on the lathe alone), and it'd be
nice not pulling the batteries (as I do now).

--
Cheers,
James Arthur