I was working on a project where I needed a cheap and efficient way to log the changing resistance of a sensor while simultaneously logging the temperature. This project is similar in many respects to the other data loggers on my site. Three prototypes have been built with the third one being a PCB. I have found this design to work extremely well for my needs.
The resistance measurement principle is based on a simple resistive divider. An unknown resistor (the sensor in my case) is attached to the top leg of the divider, while a known resistor (reference resistor) is attached to the bottom leg of the resistor. The voltage between the two resistors (V_out) is then measured and stored on an SD card. The stored voltage data is then manipulated in MATLAB and converted into a resistance value based on the size of the reference resistor. The SD card is able to hold both the collected data from the Arduino and the MATLAB script used for converting the data into resistance. Keeping the MATLAB script on the SD card allows for easy and convenient data processing without having to keep a data processing script in a separate location.
This project is far from finished. However, I would encourage you to look at my pictures, schematics, and codes. Take what you need, and feel free to change or modify them to fit your needs. My goal is simply to make this resource available to anyone who may find it useful.
Three stages of prototypes are shown above.
Feel free to copy and/or change the script as needed. Again this in not a finished project, but a resource for anyone interested in this kind of project.