Load Cell, INA128, Uno : Counting coins by weight

good evening,

i have been using tutorial:


http://sciencestuff.xperiment.mobi/2012/04/19/measuring-weight-via-usb-with-electronic-kitchen-scales-and-the-arduino/

to use load cell kitchen scales , measure analogue output reading when increase pressure load cell. counting coins weight.

i have wired says , installed firmata software.

however, readings analog5 fluctuate between 18 , 19 without pressure applied. have looked @ similar problems on forum , getting myself confused. (i absolute novice @ this...op amp theory still getting head around).

from gathering, rg should less 10k ohms due gain formula  g=1+{50kohms / rg]. perhaps need higher gain decreasing resistance on pins 1 , 8 of amp?

what reasonable resistance then?
am missing basic tutorial?
could soldering cause of problem?

here data sheet texas instruments: www.ti.com.cn/cn/lit/ds/symlink/ina128.pdf


ultimately want plot data on graph correlates voltage on number of coins, that's few steps ahead now.

any advice appreciated.

james

hi, did load cell have measuring plate fitted on top of cell, have think 0 offset.
do changing readings whent apply mass assembly?
you can offset correction externally potentiometer or sketch.


[soapbox] sorry projects 1 have mentioned worries me when writer cannot supply circuit diagram, connect b, c d, must designer ikea.[/soapbox]

tom.....

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