On Nov 20, 9:55*pm, "Martin Riddle" wrote:
wrote in message

...



On Nov 20, 8:45 pm, Jeff Liebermann wrote:
On Sun, 20 Nov 2011 16:47:25 -0800 (PST), "Ron D." wrote:

I have a cheap Caliper too and it recently went flakey.

I did my standard trick: *Remove battery. *Short battery contacts:
Insert new battery. *Worked.

My cheap electronic caliper goes nuts when I transmit on UHF anywhere
near it. *However, it doesn't require the battery removal ordeal to
recover. *I just reset to zero and continue.

Mine uses an LR44 and you HAVE TO use an LR44, not a substitute
battery that you can get a Radio Shack.
Mechanically they are not the same.

I beg to differ. *The general package name is LR44 in an 11.6mm dia x
5.4mm thick package alkaline cell. *There are slight variations, but
the IEC LR1154 equivalents (LR44/LR154, A76, 157/303/357) are all the
same size. *Where you can have problems is that the SR44/SR1154
silver
oxide cells come in the same package. *They have about 50% more
capacity and a much flatter discharge curve. *Some of the cheapo
calipers crap out below about 1.4V. *The alkaline battery has plenty
of capacity left at 1.4V, but the caliper doesn't want to run. *If
your caliper cames with a silver-oxide cell, it should probably use
silver oxide batteries. *If it came with alkaline and has a short
battery life, it might be worthwhile trying silver-oxide. *If you're
ambitious, it might be useful to run the caliper off a bench power
supply and check how low a voltage will work.

I just measured a Harbor Freight (Chinese) 8-incher.

Drain: 13.5uA (off), 14.5uA (on)
Battery low threshold (blinking display): 1.37V
Lowest operating voltage: 1.01V

So, it's clearly made for silver-oxide cells. *The battery low
threshold is set appropriately for a silver oxide cell (e.g. SR-44).

It's a lousy threshold for using alkalines--they're barely broken in
at that voltage.

14.5uA means a year from a silver oxide cell--that's not horrible.


Why bother including an on off switch?

It's really not worth it for 1uA.

If I designed these, I'd shoot for 2uA active draw, like the
Mitutoyos, and set the battery low threshold at 1.1V (for alkalines).
The battery consumption is the biggest fault with these. Apart from
that, they're impressive.

I sometimes think about wiring up a "AAA" or solar cell and just
forgetting it, but for $0.50 a year it's not worth the trouble.

--
Cheers,
James Arthur