So I'm not sure if it is well known in the electronics/Arduino circuit, but the Arduinos are getting a big following in the home brewing world. I myself am not the most savvy person when it comes to utilizing the power of the Arduino, but I do recognize its ability along with its limitations.
So my goal:
To use a load cell to monitor the weight of an object suspended in a liquid to determine the change in specific gravity over time. This will be used for home brewing where I intend to monitor the fermentation of my beer until it has reached its "terminal gravity" as brewers would call it.
The Set up:
Arduino Uno (hopefully)
http://www.amazon.com/American-Weigh-Scale-Ac-100-Digital/dp/B003O5K3JQ/ref=sr_1_1?ie=UTF8&qid=1394680597&sr=8-1&keywords=ac-100+digital+scale (100 gram scale - capacity in .01 gram increments)
1NA125P Inst. Amplifier
Appropriate extras to accommodate circuit
LCD (For temperature/specific gravity readout)
SD card shield for data logging (Added for future use)
So really this is a multifaceted question, but my first question (and the point of this thread) involves the feasibility of this small project.
First the AC-100. I broke it open and checked out the load cell. It is a four wire load cell that runs at 2.4v excitation, with 10.4mv output at full load. For testing purposes I have left the AC-100 intact.
Planning on running the excitation voltage to the load cell at 5v from the 1NA125P with a gain of roughly 250 to get a full 5v resolution from the sensor circuit to the Arduino. This will be adjusted from a trimmer pot before connecting to the Arduino.
Measuring different objects in air, then pure water, then a solution of sugar water. My observation from doing this is I am seeing roughly a .5 gram change for every 10 points of change in specific gravity from the object I am currently using. The unfortunate thing about this is this leaves the 10 bit resolution of the Arduino Uno just a little lacking in measuring the specific gravity for what I want. It would be able to measure every two points. I would like it to measure every one point of specific gravity, or 1.001.
My resolution is to take the 2.5vref pin from the 1NA125P to the aref pin on the Arduino. My logic says that should double my measured resolution from the load cell if I leave the gain from the 1NA125P the same. If I take an object, who's weight is 100 grams and has a density of 1.5. CPVC for example. Then suspend that object in pure water its weight should be roughly 33.33 grams measured from the load cell. If I were to change the density of the water to 1.001 my expected weight of the object in the water should be 33.2667.
Does this logic makes sense? I would love to hear that it could work, or if there is a better solution I would love to hear it.
Thank you in advance.