Open Colorimeter Electronics

Open Colorimeter Electronics


The Open Colorimeter uses STEMMA QT connectors. Communication with peripheral devices via I2C using 4-wire cables with JST SH connectors, such as  Sparkfun Qwiic or Adafruit STEMMA QT,  is rapidly becoming a standard on new development boards. This standardized cabling allows multiple sensors to be connected to the development board without any soldering.  By using these standardized connectors our colorimeter compatibile with the large and growing variety of development boards that support this standard.  For example Adafruit Feather RP2o40, FeatherS2, Sparkfun Qwiic ProMicro, Sparkfun RedBoard Qwiic and many others. It will also work with the larger 4-pin STEMMA connectors with a JST PH to JST SH adapter cable  so that development boards such as the PyBadge and PyGamer can be used - both of which are ideal for making standalone instruments. For those wishing to use the Raspberry Pi  a Qwiic HAT adapter is available from Sparkfun.  

LED Boards

We designed a complimentary LED board with approximately the same form factor as the Adafruit light sensor board.  The LED board is connected to the light sensor board via a 4-pin cable and JST SH connectors. The open hardware KiCad design files can be found here:


  • Dimensions: 25.4 mm x 20 mm x 1.6 mm
  • Two 4-pin JST SH connectors
  • Four M2.5 through holes for mounting to the cuvette holder
  • Surface mount LED and resistor. Any 0603 LED can be used here. We currently have the following options available: white, 470nm blue, 520nm green and 632nm red

Colorimeter LED board with STEMMA QT for connecting to the Adafruit STEMMA QT TSL2591 High Dynamic Range Digital Light Sensor board via a 4-pin cable and JST SH connectors.

Additional LED info from manufacturer spec sheets

White LED

  • Luminous intensity: 850 mcd (typ.)
  • Viewing angle: 130°
  • Mfr Part #: NCD0603W3

Blue LED

  • Peak wavelength: 468 nm
  • Dominant wavelength: 465-475 nm
  • Bandwidth: 25 nm
  • Luminous intensity: 28.5 mcd
  • Viewing angle: 120°
  • Mfr Part #: 19-217/BHC-ZL1M2RY/3T


  • Peak wavelength: 630 nm
  • Dominant wavelength: 618-628 nm??
  • Bandwidth: 20 nm
  • Luminous intensity: 100 mcd
  • Viewing angle: 120°
  • Mfr Part #: E6C0603URAC1UDA

Green LED

  • Peak wavelength: 516-525 nm (typ. not reported)
  • Dominant wavelength: 513-528 nm
  • Bandwidth: 15 nm
  • Luminous intensity: 210-430 mcd
  • Viewing angle: 120°
  • Mfr Part #: SZYY0603G

Light Sensor Board


  • We are currently using the Adafruit PyBadge, though the PyBadge LC and EdgeBadge are also supported
  • We decided to use the Adafruit PyBadge as our initial target hardware platform. The PyBadge has a 160x128 color TFT display, Lipo battery connector with recharging capability, a 4-pin I2C connector for connecting the light sensor and on/off switch and buttons for user input.  In addition, the PyBadge can run circuitpython making firmware development quick and easy
  • As we described above, the light sensor and LED are connected to the development board via an I2C connection with a standardized STEMMA-QT/Qwiic connector. Thus no hardware changes are required when switching to boards and only very minor changes are required to the firmware in order to accommodate a different screen size.The I2C devices connected via STEMMA-QT/Qwiic connectors are chainable making it easy to modify by connecting to additional sensors and actuators for even more advanced customization!