New PCB design: UV sensor board for the Open Colorimeter

Joanne Long -

In this post we are sharing a new UV light sensor board design for the Open Colorimeter. The UV sensor we are using in this design 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
  • It has a compatible form factor for our Open Colorimeter
  • No extra circuitry is required
  • The sensor is in the right price-range ($11 per sensor) and is available at online electronics vendors such as Digikey and Mouser

All of these features were taken into consideration in our selection of the AS7331 sensor as a UV sensor board for the Open Colorimeter.

Left Panel: Image of the AS7331 sensor from the manufacturer's website; Right Panel: Image of UV detector layout from the AS7331 datasheet
Figure 8: Normalized Spectral Responsivity of the AS7331. Image from AS7331 datasheet.
AS7331 - spectral UV-A/B/C sensor IC - ams
The AS7331 is an integrated circuit for spectral UV-A/B/C sensing. The sensor is optimized for reflective, transmissive and emissive measurements of artificial or natural UV radiations.
ams

Applications of UV Spectroscopy

When paired with a UV LED, the UV sensor can be used in UV spectroscopy to quantify or monitor compounds that absorb in the UV range. For example DNA Quantitation by absorbance at 260nm or nitrate and nitrite measurements in water. UV spectroscopy requires using a quartz cuvette or UV-transparent disposable cuvettes.

The principle of Ultra Violet (UV) Spectrophotometer
Ultraviolet-visible spectroscopy is considered an important tool in analytical chemistry. In fact, this is one of the most commonly used…
MediumAnkur Choudhary

PCB Design

The PCB was designed in KiCad and the design files are available under open source licenses in out Github repository. An image and link to download the schematic are below:

Link to Schematic

PCB Layout

We designed the PCB to be compatible with the Open Colorimeter so it can be easily swapped out to replace the current Adafruit TSL2591 visible light sensor with the UV version. We used the same 1.0 x 0.7 inch PCB dimensions, same mounting holes, STEMMA QT connectors and light sensor location. The board can be operated from 3.3-5V and contains an on-board 3.3V regulator. The device IC2 address can be adjusted via 2 jumper pads located on the back side of the PCB (in case of address conflict).

IO Rodeo AS7331 UV ABC Sensor: Front of board
IO Rodeo AS7331 UV ABC Sensor: Back of board
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Next Steps: Alongside testing of the AS7311 UV board we are also developing compatible UV LED boards. Stay tuned for updates! We would also be interested to hear from community members interested in using UV measurements in work and projects. Email info@iorodeo.com or comment below!