Light Sensor Boards

As mentioned in the product overview, the different Open Colorimeter instruments utilize different light sensor boards. On this page we will go into these sensors in more detail.

All of the light sensors used with the Open Colorimeter have the same form factor and standard 4-pin JST SH connectors (also called STEMMA QT or Qwiic). They connect to the LED boards in the same way and so can be easily interchanged.

Open Colorimeter TSL2592 Light Sensor Board

Image shows the TSL2591 connected to an LED board

Adafruit TSL2591 High Dynamic Range Digital Light Sensor is a broad range light sensor. This is a highly sensitive, broad-range visible-IR light sensor. Highly configurable with adjustable gain and integration time.
Instruments: Used in the Open Colorimeter and Open Colorimeter Plus
Learn more: The open hardware design files and lots of other documentation can be found here: https://learn.adafruit.com/adafruit-tsl2591
Firmware: https://github.com/iorodeo/open_colorimeter_firmware

Multichannel AS7341 Light Sensor Board

Image shows the AS7341 connected to an LED board

The AS7341 light sensor is an multichannel light sensor. 8 channels cover the visible light spectrum from 415-680 nm (channels F1-F8). There is also an additional near-IR (NIR) channel and a clear channel (no filter). The visible and NIR channels use filters resulting in the spectal responsivity curves shown in the image below (taken from the datasheet).

Fig 17 in AS7341 datasheet. Normalized Spectral Responsivity

Optical characteristics of the 8-channels in the visible light spectrum. λp = typical center wavelength, FWHM = bandwidth/full-width at half max.

channel 1 (Violet): λp = 415nm, FWHM = 26nm
channel 2 (Violet): λp = 445nm, FWHM = 30nm
channel 3 (Blue): λp = 480nm, FWHM = 36nm
channel 4 (Green): λp = 515nm, FWHM = 39nm
channel 5 (Green): λp = 555nm, FWHM = 39nm
channel 6 (Orange): λp = 590nm, FWHM = 40nm
channel 7 (Red): λp = 630nm, FWHM = 50nm
channel 8 (Red): λp = 680nm, FWHM = 52n

The 8 channels cover the visible spectrum from approx. 400-675 nm with some overlap between channels. The FWHM (bandwidth) for the channels ranges from 26-52 nm.

We plotted the center wavelength for these 8-channels on the visible light spectrum so you can visualize the channels as well:

Image modified from Gringer - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4639774

Instruments: Used in the Multichannel Open Colorimeter
Learn more: The open hardware design files and lots of other documentation can be found here: https://learn.adafruit.com/adafruit-as7341-10-channel-light-color-sensor-breakout/overview
Firmware: In development

UV Colorimeter AS7331 Light Sensor Board

The UV sensor we are using is the ams-OSRAM AS7331 Spectral UVA/B/C Sensor. The AS7331 sensor provides a low noise all in one solution for measuring UV light between 230 and 430nm. It has a huge dynamic range and three separate channels for UVA, UVB and UVC optical radiation.

Some additional features:

The sensor communicates via an I2C interface and has 4 adjustable I2C addresses
The responsivity of the sensor can be set using Gain (12 steps), conversion time (15 steps) and internal clock frequency (4 steps). Each of these values is adjusted by a factor of two for each step
No extra circuitry is required

Left Panel: Image of the AS7331 sensor from the manufacturer's website; Right Panel: Image of UV detector layout from the AS7331 datasheet

Normalized Spectral Responsivity of the AS7331. Image from AS7331 datasheet.

Learn more: Links to the open hardware KiCad design files and other documentation can be found here: https://blog.iorodeo.com/uv-sensor-board-for-the-open-colorimeter/
CircuitPython library: https://github.com/iorodeo/iorodeo-as7331
Firmware: https://github.com/iorodeo/uv_photometer_firmware

Open Colorimeter Product Guide

Documentation site for the Open Colorimeter, Multi-Channel Colorimeter, UV Open Colorimeter & Open Colorimeter Plus

Product Guide Home Page