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I have an SEN-10245 sensor for weighing objects (essentially a strain gauge). The goal is to capture data with a Raspberry Pi, so the signal from the weight sensor needs to be amplified and then ran through an Analog to Digital converter. I have the AD620 InAmp paired with a 47 Ohm resistor to set the gain to ~1000, which is then ran through the MCP3008 Analog to Digital Converter. I then hooked the converter up to the Raspberry Pi following this Adafruit tutorial

Question: Where should the red black and white leads of the load sensor be connected; this is the signal that needs to be amplified by the InAmp.

AD620 Data Sheet

MCP3008 Data Sheet

The pictures below illustrate my current setup:

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enter image description here

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You need to use the sensor in one-half of a wheatstone bridge circuit. The other half can be made from two reasonably identical resistors forming a potential divider like the strain gauge does.

+Input of instrumentation amp to centre point on resistors and -Input to centre-point of gauges: -

enter image description here

The two 350 ohm resistors that feed the lower input are the two reasonably identical resistors. Your strain gauge is the two resistors to the left feeding the upper input. In fact the inputs can be reversed. Ensure your power rails are sufficient for the AD620 - remember the common mode range that this amp needs is: -

(-Vs + 1.9V) to (+Vs - 1.2V) so if you operating it from a 5V rail and ground it should be OK because the mid-points of the voltage dividers are at ~2.5V give or take a few tens of milli volts.

Black = lower end of the two left resistors, white = upper end and red goes to the IA input. You'll also need to connect the reference input to (possibly) half rail and note that it is usually reasonable to use the junction of the two reasonably matched resistors and maybe add a 10uF cap to ground but check the IA data sheet on this.

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  • \$\begingroup\$ Thanks Andy! I actually have another sensor, so can that be used for the second half of the wheatstone bridge? I also found this article (jcehle.com/bees/2013/10/16/sensing-weight-with-raspberry-pi) with nearly the same setup, but no wheatstone bridge. Is the bridge absolutely necessary in this case? \$\endgroup\$ – Anconia Mar 26 '14 at 22:42
  • \$\begingroup\$ @Anconia quote from that site "The current setup uses two of these units to form a complete wheatstone bridge". A bridge is advised to reduce offset errors versus temperature but a half bridge is OK (as per your setup). \$\endgroup\$ – Andy aka Mar 26 '14 at 23:01
  • \$\begingroup\$ Ahh, sorry about that! \$\endgroup\$ – Anconia Mar 27 '14 at 1:19
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According to the comments on Sparkfun's page for that strain gauge, the black wire is ground, white is +5, and red goes to the instrumentaion amp input.

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