Using multiple strain gauges for digital scale

[jBernard]

fcb,
if i do that, i get 2 sensors going from .065V resting to around 1V each when pressed hard, which seems to be working. then the other 2 start off at .065V and go the opposite direction when pressed hard, only down to .059 or so.

[jBernard]

Treat pin 6 as a zero adjustment and stick a pot in there if its not outputting a nice 0V,

yes the 10 and 30K resistors are internal circuitry

as for no detection, you will likely need to fit a gain resistor as per the datasheet, as the signal of you pressing it may be quite small in comparison of the maximum deflection of the strain gauge

not sure if i understand the concept behind the pot on pin6. do you mind explaining?

[fcb]

Lets break it down.
a. Each 3 pin strain-gauge 'module' is actually a pair of gauges setup as potential dividers.
b. As you step on the scales, one half of the potential divider will decrease in resistance and one will increase.
c. You have four of these modules for the scale.
d. You need to configure two of these so that the voltage rises with applied pressure and two of these so it falls.
e. Once you have this working, then you can sum the pairs.
f. Measure the (differential) voltage between the summing points, it should 0V with no weight, and measure something when you step on the scales (say 20mV).
g. You now have a wheatstone bridge.
h. Apply the two summing points to pins 6 & 7 of the INA125
i. Calculate Rg according to the INA125 datasheet.

Other issue(s):
You have the reference set for 5V - you know you will need more than 5V for your supply?

[jBernard]

i had 2 sensors working a bit ago. now i'm not getting a reading due to not knowing how to pair the 2 sets together. if you could explain how/if pairs of wired are tied together for the + and - sides that would help.

and on the supply voltage. i'm using the 3.27v input i have being sent from the arduino. i was under the impression that the strain gauges were like a pot, and didnt need a specific voltage, and that the INA125 would operate fine on that voltage as well. but i may be wrong?

[fcb]

i had 2 sensors working a bit ago. now i'm not getting a reading due to not knowing how to pair the 2 sets together. if you could explain how/if pairs of wired are tied together for the + and - sides that would help.

and on the supply voltage. i'm using the 3.27v input i have being sent from the arduino. i was under the impression that the strain gauges were like a pot, and didn't need a specific voltage, and that the INA125 would operate fine on that voltage as well. but i may be wrong?

I think you should have posted this in the Beginners forum.
1. Read the INA125 datasheet.
2. A single strain-gauge is a variable resistor, it looks like you have two strain-gauges arranged as potential divider at each corner.
3. I've already explained how to wire them together - you're very close with the last drawing.
4. INA125 in your config. is driven from the 3v3 from the arduino, your BG reference is wired for +5V and unused. Why did you do this?
5. It doesn't matter which corners you pair up. Think it through!

[jBernard]

thanks for the reply.

-i've made some changes and paired some of them together, have 2 of the sensors working on the + side, the - side works but not like i had figured.
-took the 4->15 jumper off, and taking ref for the sensors off the 2.50V pin 4 of the amp now.

on the + side i get a decent swing on ouput of the amp, .06V resting to decent press of .5V on each of the + sensors.
on the - side i get .06V resting, pressing hard on each goes down to .048V

heres how i have it wired. 2 sensors sense leads going into - amp input, with their + and ground wires reversed from the + sensors.

[Andy Watson]

on the + side i get a decent swing on ouput of the amp, .06V resting to decent press of .5V on each of the + sensors.
on the - side i get .06V resting, pressing hard on each goes down to .048V

What are you expecting the output to go down (or up)  to?

When you have an answer you might consider pulling up the datasheet and have a good think about what pin 3 does.

[jBernard]

well this sounds beginner, since i am, but on the old sensor having it setup, we didnt try to reach a specific voltage on a specific weight. we just calibrated it for the weight. so if it was .060V unweighted and 1.200V weighted with 5#, the output was linear so we could derive all other weights (as accurate as we needed) from that scale.

[jBernard]

bump. any help/advice appreciated!