On Wed, 15 Apr 2009 01:49:36 +0000, DoN. Nichols wrote:
On 2009-04-15, James Waldby ... wrote:
On Sun, 12 Apr 2009 03:00:06 +0000, DoN. Nichols wrote:
On 2009-04-09, James Waldby ... wrote:
On Thu, 09 Apr 2009 22:31:31 +0000, DoN. Nichols wrote:
[...] B&S 0-6" digital calipers (now not usable because
they need PX-13 mercury cells in a holder which would not
be happy with any modern cell [...]
A WeinCell MRB625 battery is supposed to be a proper $4 substitute
for a PX-13 mercury cell,
But since the B&S caliper needs *four* of them, that is a $16.00
replacement. (It is a "DIGIT-CAL II", FWIW.) [big snip]
[...] "the WeinCell is not activated until the
pull-tab is removed (removing batteries from equipment and replacing
tabs prolongs battery life)." ...
Snapping off the battery holder, removing two small Phillips
screws, removing the four cells, and relacing the tabs -- certainly
sounds convenient. :-) Well ... three of the four cells are held +
side up, visible through apertures in the holder, but (assuming that
is the surface with the holes to be covered) that still leaves one
which requires the same disassembly sequence.
True, putting the tabs back on doesn't sound like an easy fix for
longer battery-life in that caliper. I included that bit in my earlier
post not because it's useful, but because it's amusing that the seller
suggests it. However, it might be practical to store the caliper in a
box purged with nitrogen, argon, or CO2.
Hmm ... if I had a TIG welding setup, the argon would be a good
choice (along with machining up a metal case with an O-ring seal and a
fill and vent valve). I wonder what would happen should I pump it down
to a fairly good vacuum (other than it leaking air back in over time). I
wonder whether the cells are allergic to vacuum.
I thought of vacuum also. A minute or two with google didn't answer
that question, although it gave lots of links to old hearing aids that
used a vacuum-tube rather than transistor, and vacuum-cleaners for
hearing aids, and remarks that putting the tab back on a zinc-air
hearing-aid battery apparently doesn't extend its life. You could see
if a WeinCell survives vacuum ok and let us know
[...]
Depending on what the current draw is and how stable it is, you might
be able to use something like the dual-diode BAV199 in a 0.05"x0.12"
SOT-23 package. [to drop 6V from 2 li cells to 5V]
Hmm ... I've not measured the current draw yet -- but I suspect
that there will be a significant variation from displaying '1's to
displaying '8's, since it is a LED readout, not LCD like most more
recent ones.
I misunderstood that earlier, and thought the LED referred to was used
in position sensing, which would have a more stable current. But with
an LED display, not only could there be large variations in current, it
also might over-tax 2032 coin cells. Perhaps consider using four NiMH
AAA's, for example lined up in a tube attached to the underside of the
caliper. That would deliver about 5V through most of the discharge
curve. Or maybe find a flat rectangular cell-phone battery the right
size to attach on the back of the caliper, and use an LDO regulator
(like TC10145.0VCT713) to get 5V.
[...] Of course if you've got those germanium
diodes already, wouldn't 3 in series be about right?
About, yes.
(Per, eg, (http://baec.tripod.com/articles/crystal.htm) [...]
Hmm ... he is using unfamiliar diode part numbers, except for
the mention of the US 1N34A (which I have used in the past).
The mention of the gold bonded diodes reminded me of my first
employer -- Transitron -- who got their start in the semiconductor
industry by making good quality gold bonded diodes. I *think* that they
actually invented the process. At the time, they were used heavily in
logic circuits by the then growing mainframe computer industry. By the
time I was working for them, they were making lots of silicon diodes and
transistors -- in competition with Texas Instruments. I also remember
interesting variants on the diodes called "stabistors" -- made
specifically for the stability of their forward voltage drop -- and the
temperature coefficient of that forward voltage. They were combined
with a zener diode with the opposite temperature coefficient, and a
selected transistor to make what was sold as a "ref-amp" (reference
amplifier) which had a precise and stable forward voltage drop from the
base out the emitter, and through the zener and the stabistors to
provide a very stable reference, and to amplify any variation applied to
the base to control a voltage regulator. The transistors, zeners, and
stabistors were all tested in large racks under silicone oil at -50C,
50C, and 150C, and it was fed into a very expensive (at the time)
mainframe computer to spit out selections of which ones would give the
most stable results. (Sometimes, some would give poor results at
intermediate temperatures, as I remember having to test some returned
units as they were cycled through the full range from -50 C to +150 C,
and which meant that I had to use a mix of silicone oils, as that used
at -50 C would boil at +150 C, and that used at +150 C would become
rather hard silicone grease at -50 C. :-)
I think that the company name is still around, but that they
don't make semiconductors now.
They also had another device -- a 4-lead device in a TO-5 can
which they called the "binistor". It was a mesa style silicon
transistor with an extra lead bonded wrong -- overlapping two zones, and
it behaved as a bistable device. So -- you could make a flip-flop with
a single device -- before integrated circuits allowed it in a single
chip. :-)
I've heard of Transitron and stabistors, but don't recall binistors, even
though I've got some 4-leaded parts with specs like that, from ca. 1966.
It sounds like Transitron may have been an interesting place to work!
'Til next week -- off to Arches and Canyonlands tomorrow --
--
jiw