measuring weight using hacked scale + INA128 + firmata --- help!

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hi,

i hope ok post basic 'newbie' question.  i'm food scientist / psychologist , exploring possibility of using arduino uno + sensors in food science & psychology research.  @ mo, i'm trying measure weight via arduino.  end objective post blog fellow 'no electronic skills' scientists others can build such devices.  i'm linking arduino research software writing (www.xperiment.mobi).

after googling, although not find clear guide how build this,  settled on guide http://forums.netduino.com/index.php?/topic/1284-connecting-a-beam-load-sensor-to-netduino/.  post:
quote

this ic have ina128p. @ schematic on first page.
1. connect s- pin 2 of ina128, connect s+ pin 3 of ina128.
2. if have bread board connect netduino +5v , ground pin power rails on bread board.
3. connect e- , e+ breadboards power rails.
4. connect pin 7 on ina128 +5v rail.
5. connect pin 4 , pin 5 of ina128 ground rail.
6. either use resistor gain want or did , use pot variable resistor. use multi meter determine 2 pins of pot show resistance change when turn pot , connect pins 1 , 8 of ina128.
7. connect pin 6 of ina128 analog pin of netduino.


i bought these:
-cheap electronic weighing scales tescos http://www.tesco.com/groceries/product/details/?id=262683786
-ina128 amplifier.  here's info on it: http://www.ti.com/lit/ds/sbos051b/sbos051b.pdf

i dismantled electric scale , soldered 4-wires strain gauge thicker wire (to let me more interface bread board).  luckily, wires appropriately labelled on existing circuit board:


as shown in image (slightly photoshopped make things more clear, such 1 wire interfaces each of pins of amplifier), linked breadboard advised in post (i've used 100ohm resister, tried using variable resister).  running arduino loaded firmata standard, , running firmata test program (http://firmata.org/wiki/main_page), nothing - analog pin fluctuates around '400', , same degree unused analog pins do.  pressing down on sensor nothing :( .  check had not blown strain gauge resoldered weighing scale , still works (rather incredibly).

i appreciate on this, , patience limited knowledge of electronics.  doing silly. 
with many thanks,
andy.

i check wiring:

this ic have ina128p. @ schematic on first page.
1. connect s- pin 2 of ina128, connect s+ pin 3 of ina128. - ok
2. if have bread board connect netduino +5v , ground pin power rails on bread board.- ok
3. connect e- , e+ breadboards power rails.- ok
4. connect pin 7 on ina128 +5v rail.- looks have connected pin 6 +5 me
5. connect pin 4 , pin 5 of ina128 ground rail. - looks me have used 4 & 8
6. either use resistor gain want or did , use pot variable resistor. use multi meter determine 2 pins of pot show resistance change when turn pot , connect pins 1 , 8 of ina128. - looks 1 & 5
7. connect pin 6 of ina128 analog pin of netduino. - looks 7


i think perhaps misunderstanding pin numbering.  in photo, pins number anti-clockwise bottom left top right:

 8 7 6 5
|-------|
d         |
|______|
1 2 3 4


Arduino Forum > Using Arduino > Project Guidance > measuring weight using hacked scale + INA128 + firmata --- help!


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