I did some searches on cuvettes, photometers, and optical setup ideas. The next phase is to depart from the Yang et.al. approach and the 100ml sample cell and try for a 3ml cuvette as the optical cell. Second, I want to run the photometer directly from linux on an rPi3 and use a 16 bit ADS1115 AD integrated circuit to read the TS257 light sensor. That will put an entire operating system at the disposal of the photometry package and free up an Arduino UNO for prototyping. If I go back to arduino, I’ll use a Nano from Xina.
Below – cuvette cell prototype design- you can see the “port” for the light path here… V2.1
v2.1 of the 3ml cuvette and optics electronics.
Below: this design has design elements along the lines I’m looking for – http://www.instructables.com/id/An-Inexpensive-Photometer-and-Colorimeter/
I can see this working for the mini-photometer but using the blue and green leds.
Below, a flow-thru cuvette – the sample is injected into the cuvette for the blank shot. The water is released, mcp dye is mixed in and then the dyed sample is re-injected back into the cuvette to obtain the absorption numbers. Flush.
Below – http://nznano.blogspot.com/2011/12/homemade-spectrometerspectrophotometer.html — the cuvette holder/breadboard prototype …
OceanOptics https://oceanoptics.com/product/trans-ph-kit-series/ produces a kit for measuring pH using spectrometry, measuring the color change of a disposable “patch”. They do not rely on an absorption method or mcp dye. The method requires calibration – a lot of calibration.
Other hardware they manufacture provides some ideas for the physical setup. .
Nice looking optical cell components from oceanoptics below, and a schematic diagrams showing the use of fiberoptics. The main challenge will be to get the light intensity values in the LED’s right with the short ( 10mm ) light path.
Another cuvette holder cell
… Below- v2.1 cuvette holder. built today 4/27/17 and painted black to contain the light path. Also inserted some spacers to hold the cuvette tight. It has to be very tight. Remounted the LEDs and TSL257 light to voltage unit somewhat better than the original shown here.
The v 2.1 arrangement provided proof of concept so a second v 2.2 holder was built and tested in the lab. The results are good enough to validate the overall design and also showed that the cuvette holder design is critical to getting to a +- 0.01 pH photometer. This one has too much wiggle room, literally, to get to +- 0.01.