nimum values
The same process has also been measured with the photometer. The sensor gives you two values: a full spectrum value (Full) and a value of a second incorporated sensor which measures only the infrared (IR) part of the spectrum. The values of the visible part of the spectrum (VIS) can be estimated by subtraction of IR from Full values. The dye used here was phenol red, which is yellow in acids, red under neutral and violet under basic conditions. Its pKa is also around 7.0. The light source used here was a green LED, so the increase in "redness" resulted in a diminished amount of green light reaching the sensor.
Step 6: Example #2: Dilution Curve (photometer)
The second example is a dilution curve of a red dye.
As shown in the image, a serial 1:2 dilution was set up, with an additional blank value. The dilutions were measured from the lowest to the highest concentration, using the photometric sensor (TSL2591) and a green LED (Nichia NSPG500DS) as the light source. The measured values were written to a CSV file and analysed using LibreOffice Calc.
The resulting lin-log graph (linear: absorption vs. logarithmic: concentration) gave the typical S-shaped curve seen in such measurements. At low concentrations there is a direct relationship between concentration of the dye and absorption of light, while at higher concentrations it is asymptotically approaching a maximum level (total absorption). Using the curve, the usable detection range can be estimated to cover about two logs (100x) of concentration, which is reasonable for a photometric device.
Step 7: Some Final Remarks
- To make the devices described here available to the public, we are planing to place a optimized, checked and proved layout file for the acrylic parts at Pokono, so you may download it there for a small licence fee. I would like to insert a few changes to the current layout, which may require a few weeks to be evaluated.
For all that want to start right now: A slightly modified version of the last evaluated one is available at Ponoko.
The licence fee for the layout shall be used for this project, as I would like to give a number of the devices for an evaluation to schools or other other educational institutions.
- But as collecting all the required parts from different sources could be a hurdle, we think about setting up a small project to offer DIY kits that would alredy contain all parts, except for the Raspberry Pi, plus some cuvettes and consumables, so you may built your own device within a few minutes and start immediately with your first experiments.
So you might see a kickstarter project on this soon, and if you are interested in such a kit, please check this site again in late May.
- The part that may require the largest improvements is the software. I would appreciate if some skilled programmers would check my Python scripts and improve them. I would like to place links to your improved scripts in here, for public access. Please be aware that the basic scripts are licenced by Adafruit under the MIT licence, so any derivate should be as well.
- In this instructable I have used a few graphs taken from Adafruit and the data sheets of the sensors.
But there are also images I have copied from the web, but have lost the information from which sites. I would like to apologize for this and thank the owners of the images.
- If you like this project, please have a look to my other instructable on a Raspberry Pi-based microscope (Raspberry-pi-microscope ). The project got stucked a bit in the last months, as I have a busy full time job and a family, but may see some new developments soon.
- If you have any hints, suggestions or corrections, please let me know.
Step 8: Materials Required; SVG File
Raspbery Pi or Arduino
Adafruit TSL2591 breakout (for photometer, product ID 1980)
Adafruit TCS34725 breakout (for colorimeter, product no 1334)
You may use other sensors or breakouts, but you may have to modify the position and size of the holes in the sensor holding plate.
The acrylic pieces for the housing:
The current layout was optimized to allow a