Measuring weight

[mike mager]

MysticZ <lt1_z28 at houston-f-body.org> asked about a weighing system:

Alright, well, I have disassembled just about every machine that I could 
ever get access to!;  it's my way . . .

. . . and I found . . .

I found that the low-quality/low-price digital _bathroom_ scale uses a 
spring, and a 'hidden' wheel, - just like the one with the numbers on it for 
an analog-readout mechanical model - with no numbers, but with a series of 
holes, just like a CKP.  The thing 'boots' at zero, and then counts the 
number of holes (quadrature, maybe).  Truly bogus!

I found that the higher-quality/higher-price digital _bathroom_ scales (as I 
own) use a true load-cell - no spring!  With a load-cell, it's just a 
Wheatstone bridge, so, you could buy two of them (~50USD at Fred Meyer - not 
bad for a quantity one load-cell!), install a switch and a jack, and use 
either the internal display, or the jack.  Now, the jack, here's where it 
gets fun!  You know hardware/software, right?, so just rig up a PIC, or any 
minimal analog-input MCU, and the appropriate output device (NS 5051 35-bit 
constant-current serial LED display-driver, HD44780 LCD module?).  You can 
cal the bridge at 'zero' each time, and that will take out your tare (ramps, 
paper to keep it clean, rain, whatever), just like the - oh, yes - mine is a 
Sunbeam.

I needed to read a few messages of this thread before I even understood the 
question (now it makes sense);  sounds fun, easy, useful.

Mike
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