Colorimeters are analytical devices commonly used in science labs to measure the amount of light of a specific wavelength that is absorbed by a sample. Absorbance is related to concentration (Beer-Lambert Law) so the greater the concentration (color intensity) of a sample, the greater the absorbance (A) value. Comparison of the absorbance measurements to a calibration curve provides the final concentration in the sample. In this project we have designed an open source colorimeter with an Arduino shield.

The colorimeter e ssentially consists of two electronics boards: i) a red-green-blue (RGB) LED board and a light sensor board. A cuvette holder in the center of the colorimeter properly positions the sample between the LED and the sensor. The sensor board connects to a Arduino programmed with the colorimeter firmware via a simple colorimeter shield. When the colorimeter is operating, the RGB LED illuminates the sample in the cuvette with one of three different wavelengths of light:

A small slit in the colorimeter allows light to pass through the sample to the light sensor. Absorbance (A) of the sample is determined by comparing the intensity of incident light (I₀) to the intensity of light after it has passed through the sample (I) using the following equation: A = log₁₀(I/I₀).