The develop4wash team has been working on constructing a self-contained, sealed turbidimeter using off-the-shelf components.
Here’s what it looks like so far:
Internally, the unit is powered by an Arduino Uno microprocesser/development board and two TSL2561 luminosity sensors from Adafruit. Bluetooth connectivity is provided by a Virtuabotix Bluetooth module. The unit is designed to hold a single 1″-diameter sample vial and currently uses a two-point calibration routine to scale the “arbitrary units” sensor readings to the internationally-accepted NTU standard.
The following data was collected using fairly volatile samples being switched between a calibrated commercial turbidimeter and the prototype unit. Although accuracy is not yet up to the .05 NTU standard laid out in our original spec, a linear region does appear to exist in the 0-40 NTU range as outlined in the EPA’s documentation. The blue line is the calibration curve derived by the turbidimeter and used to convert sensor readings to NTU.
As usual, CAD files, images, and manufacturing instructions have been posted to the Launchpad page for the project. Code updates between major releases can be found in the “development” code branch; to-do items (and related discussions) can be found under the “blueprints” tab. Our work is open-source; if you’d like to contribute, join the develop4wash group on launchpad to start pushing updates and reporting bugs.
Goals for the next prototype:
Reduce light scatter through precision control of the light source,
Experiment with the instrumentation to discover the source of the noisy signal,
Use a machined PVC sample holder rather than a 3-D printed one (cheaper and easier to change).
At the same time, we also need to start thinking about building our own circuit board and figuring out power-saving methods for the production model.
Alex & the develop4wash team