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Fmilburn

Load Cell and INA125P Instrumentation Amplifier

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Some time back I ordered an INA125P Instrumentation Amplifier in order to fool around with a cheap, broken "postal" scale that I had.  It arrived and I promptly put it away and forgot it about it.  So the other day I was digging through my junk box, saw the scale, and decided to tear it apart.  Since it is getting near Halloween, and I knew my grandchildren would be interested, I wrote a little sketch in Energia to estimate the amount of candy in a bowl.

 

Here is a schematic of the circuit.  It "works" but given my skills it may not be best.

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This being a MSP430 project I hooked up the sleep pin on the INA125P.  I also made it where I could change out Rg, the gain controlling resistor, easily.  Once I had it working I made up a little BoosterPack that goes on the bottom of the LaunchPad. 

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The INA125P sits between the daughter board and the MSP430F5529 LaunchPad - you are looking down on the male pins in the photo above.  I hot glued a piece of cardboard on the bottom so as to reduce the chance of shorts and provide a reminder on how to connect it.  Below is a view from the bottom with it connected up to the LaunchPad and the scale.

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The sketch is here on github.  There is a little calibration routine it goes through when started up where it asks for the empty bowl and then a known quantity of candy to be placed into it.  After that, it displays on a SHARP96 BoosterPack.

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I thought about connecting it up to the IOT, but after due consideration decided I didn't want the neighborhood kids knowing how much candy I have left.

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