I have 2 straingauges, mounted on each side of a thin metal plate. I want to connect this to an opamp: http://www.sparkfun.com/commerce/product_info.php?products_id=8704 and then into analog input on the arduino. Can anyone tell me how to do this so the plate only meassures axial force.
In general, strain gauges will require a more complex setup than a simple op-amp. I think you want an “instrumentation amplifier” (which used to be built out of several op-amps, but now you can get as a single chip.) I’m not sure of the details…
The board with LMV358 is not the right one for your aplication (parameters of op-amp plus it is hard-wired). To suggest you something we need to know more details about your setup (number of wires, resistance …) Try to google some typical schematics how to use strain gauges.
its 100 ohm, the problem is that i have lost the datasheet for the strain gauges… So i have no idea of e vs. V, but its a pretty standard strain gauge, with one on each side of the plate so bending moment can be neglected. I guess I need to wire it up together with 2 resistors of 100 ohm to make a half bridge. The problem is that i have no clue which opamp to use and which wire goes where in the halfbridge to get out just the axial force.
Thx for all the help.
Well that SparkFun breakout op amp module you linked to won’t work for your application because it is an AC amplifier using capacitors for input and inter-stage coupling. You will require DC coupling for work with a strain gauge. Goggle on instrumentation op-amps and you should find various application information and circuit examples on interfacing with resistive bridge type sensors. The type of op-amp to use is not as important as the circuit you surround it with for simple DC applications. Simple op-amps can be wired to use differential input.
Be wary of change in strain due to temperature. Consider temperature compensation by mounting another strain gauge on the perpendicular axis as compared to loading. Then take the difference between your measuring strain gauge and the temperature compensating gauge and this is the strain value.
Side Note: First implement a one gauge setup before attempting to correct for temp.