weight differentiation

[gilardino]

i need to differentiate 3 different weights of the objects. load cell is expensive. I have tried strain gauge but it is not stable. Any solution? thanks.

 

[crutschow]

What are the weights, what type of output do you need, any limitations on the type of parts you can use?

 

[gilardino]

the weight can be for example 10g, 20g, 30g (small objects). The purpose is just to differentiate 3 different weights. So i need a kind of sensor to use. first my robot will grab or lift the object then differentiate what type of the object. I got try strain gauge. The resistance of strain gauge will change if any strain or object applied to it. Then i can measure the voltage. But strain gauge result gave me unstable output.

The output can be resistance changes, voltage changes or anything so that i can connect it to my microcontroller

 

[crutschow]

Strain gauges usually work well. What type of strain gauge is it and what is the circuit you are using to read it's resistance?

 

[gilardino]

aluminium type strain gauge 120ohm. The strain gauge is used as resistance in wheatstone bridge. Any changes in resistance will cause changes in output voltage of the wheatstone bridge.

I test it by attaching the strain gauge to any bend materials. So i bend it, the resistance changes gave me 121, 123, 140, 170 ohm. Sometimes, in the same bending angle, the resistances i got are different.

so i wanna try another method to differentiate the weight...Or do u know, how to implement strain gauge to get accurate resistance changes??
Thanks...