Digital Designs and Scientific Hardware - Open-Source Lab: How to Build Your Own Hardware and Reduce Research Costs - page 216

FIGURE 6.59 Screenshot showing the Xoscillo acting as a logic analyzer.

6.4 Environmental Science: Open-Source

Colorimeters and pH Meters
OSH can also be used for environmental science. In this section, we will look at designs for
an Arduino-based colorimeter and pH meter. After detailing the design and fabrication of the
devices, the quality is discussed to provide data for conclusions about future development of
other open-source analytical tools discussed in Chapter 7 .

6.4.1 Open-source colorimeter
Colorimetry is a scientific technique that is used to determine the concentration of colored
compounds in solutions by the application of the Beer-Lambert law, which states that the con-
centration of a solute is proportional to the absorbance. To do colorimetry, you need a col-
orimeter, which starts in the hundreds of dollars for a lab-grade tool. In general, a colorimet-
er is used to measure the absorbance of only a particular color (e.g. wavelength) of light for
a specific solution. A colorimeter is a relatively simple scientific device consisting of a light
source, sample holder (normally a cuvete or test tube), light intensity sensor and means of
controlling the light source and integrating transmited light intensity. Incident light is gener-
ally filtered allowing only a narrow band of wavelengths near the absorbance peak for a given
dissolved species. The method requires a blank solution for calibration (zero) and reports res-
ults in absorbance units, transmitance or if it is calibrated, it can apply the Beer-Lambert law
to report results as a concentration [ 35 ]. Colorimetric methods are used widely in research and
in many industries, including investigating the food we eat—such as during storage of bread
[ 36 ] , chocolate [ 37 ] and milk [ 38 ] . For example, in environmental science, colorimeters are used
to monitor the levels of nitrates, phosphates, metals and other compounds present in elu-
ent entering the natural environment from the manufacturing of paper and other commercial
goods [ 39 , 40 ] . They have also traditionally been used to estimate the population density of