The ROXI Colorimeter & Fluorimeter. Laboratory Application I. Colorimetric measurements via Beer’s Law.
Required Supplies & Costs: RGB LED; $1.95 Light Sensors; $3.95 ea 3-way switch; $6.54 300 ohm resistor; $0.10 Arduino Uno; $24.95
1. Sensor Description.
The sensor consists of a common cathode RGB light emitting diode (Sparkfun Electronics, https://www.sparkfun.com/products/105 ), and two logarithmic scale analog light sensors (Adafruit Industries, https://www.adafruit.com/products/1384 ). Peak wavelengths for emission by the LED are specified as 467.5, 520, 625 nm by the manufacturer. The light sensors are powered by 2.3-6 VDC, and produce an output voltage (Vout) that is linear with the logarithm of the light intensity incident upon the sensor. The light sensors are glued onto the side of a cuvette holder that was 3D printed. Two light sensors (shown in blue in figure below) are present. The first at 180 deg. to the incident beam is for transmittance / absorbance measurements. The second detector is placed at 90 deg. angle for fluorescence or light scattering measurements. A circuit diagram for the apparatus is shown below. A 3-way switch (NKK Switch, HS13Y) distributes power to the RGB LED with current controlled via a 300-ohm resistor at the common cathode. Each light detector is powered via 5VDC, and ground is common. Two analog input channels of the Arduino are devoted to voltage measurements from the sensors.
light detectors
cuvette holder
Vcc
GND