Raspberry Pi ePaper Photometer
This cheap, six-channel colorimeter features an Inky pHAT, a spectrometer breakout, a couple push buttons, LEDs, and cables.
As Dr H explains in his write-up, “A photometer basically measures the amount of light that reaches the sensor. If a beam of light passes through a colored solution or a color filter, a certain fraction of the light gets absorbed or scattered, resulting in a loss of signal compared to a blank reference… By using a multi-channel photometer you can measure the color composition of a solution, filter or surface. In analytical chemistry color reactions often are used to detect specific substances, e.g. metal ions, or the acidity/pH of a solution.”
To create his own colorimeter, Dr H leveraged a Raspberry Pi Zero along with a Inky pHAT ePaper display to facilitate low power usage. This energy conscious design was meant to field applications, where it might need to run for hours under battery power. For sensing, he's using an AS7262 six-channel breakout to measure light intensity in different wavelengths. This provides much more precise readings than an RGB-only sensor.
A pair of buttons are implemented for control: a “B” for blank calibration and “M” for sample measurement. When either is pressed, an LED shines through a pipette to measure the substance (or lack thereof), outputting a nice graph of each value on the high contrast/low power e-ink screen. This data is also stored on the SD card for later analysis.
As of now, the build looks useful, but is still in something of a prototype state, and a proper enclosure will have to wait until the future!