This post is way late:-( First I got stuck trying to find or build a Fritzing part for my TSL235R light sensor. I tried to build the part in FreeCAD but that died a couple of times on me, so I got frustrated:-( I constructed other things with FreeCAD and had no problems, but it did not like that little part:-( Then, I had some problems with my WordPress setup, the backup scripts did not want to work and all the sudden it’s five month later than when I wanted to write this post:-(
My colorimeter is basically four light sources, one RGB LED which I use as three distinct LEDs in one housing and one of the near-UV LEDs and the TSL235R light sensor, all driven by the Arduino. I did play with the light sensor for a different project before, so I had some code already;-)
The TSL235R light to frequency sensor costs about three dollars @ sparkfun. The LEDs are pretty cheap when you buy them in larger quantities;-) I usually have enough of those on hand;-) You want to keep outside light out of your device and you want to limit reflexions around your sample, I just built a Lego box and lined it with mat black construction paper. You want some clear cuvettes for your test solutions and maybe some pipettes. Usually those are only sold in packs of 100+:-( I built a little template out of scrap plywood to get the cuvettes in the same spot for each test.
The Arduino code is pretty straight forward. For each colour requested, it turns on the LED at a specified level (calibrated to the particular setup), waits a bit, counts interrupts from the sensor for one second, turns the LED off and calculates the final value. That’s done ten times in a loop just to get more data points.
I tried this setup with different concentrations of fountain pen ink and it kind of worked. But I did not keep a record:-( and now everything is dried up:-( The sketch is here: Colorimeter.tar
That’s it for the 2015 Science Olympiad posts, sorry that this last one took so long. But maybe it will be useful again at some point.
As always, have fun exploring;-)