Open Colorimeter Electronics

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: https://github.com/iorodeo/i2c_led

Features

• 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

Open Colorimeter LED Board

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.

Light Sensor Board

• The Adafruit TSL2591 High Dynamic Range Digital Light Sensor  is a broad range light sensor in a small form factor which works well with our new the cuvette holder. It comes with the standard 4-pin JST SH connectors (also called STEMMA QT or Qwiic).  
• The open hardware design files and lots of other documentation can more can be found here: https://learn.adafruit.com/adafruit-tsl2591

PyBadge

• 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!