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Developing a Simple Easy to Use Remote Sensor Evaluation Platform

Advances in MEMS technology have resulted in scores of new sensors becoming available for applications ranging from motion control to biometrics and everything in between. Projects incorporating sensors first involves research to identify potential parts. For the research phase, Digi-Key’s Sensors Product Selector is an excellent resource to identify potential sensors. Once a sensor has been identified, a typical next step is testing and evaluation. Let’s face it, testing a sensor at your workbench is just the starting point. One can verify communication and functionality, but it’s preferable to test in the actual environment the sensor will see.

Figure 1. Sensor Evaluation Platform Deployed at Digi-Key Electronics. (image source: Digi-Key Electronics)

The scope of this project was to develop a flexible evaluation platform that could easily adapt to multiple sensors, wirelessly send test data back to the user, and use readily-available off-the-shelf hardware from Digi-Key. Zigbee protocol was chosen for wireless data communication since it allows multiple independent radios on the network and the mesh capability provides increased range and network resiliency. I decided to use an outdoor environmental sensor for a test project deployment of the evaluation platform since our location (northwestern Minnesota) provides a wide variety of weather conditions.

Sensor Evaluation Platform

Digi’s Xbee3 Zigbee module is the intelligent controller for the platform. Reasons for selecting the Xbee3 include the ability to act as a standalone embedded controller, it incorporates Zigbee radio wireless communications, and it supports FOTA (firmware over the air) for remote updates. For ease of set-up, the Xbee3 is plugged into an Xbee Grove development board that brings out the Xbee3 I/O to Grove connectors for easy access.

Figure 2: Sensor Evaluation Platform. (image source: Digi-Key Electronics)

The Zigbee radio hardware was mounted inside an IP65 rated PN-1323-CMB Bud enclosure so the platform could be placed in an outdoor environment. TE Connectivity M8 panel mount connectors were used to provide external interface to an I2C bus and 5 V power. An Amphenol 336320-12-0250 u.FL to RP-SMA panel mount adaptor was used to connect the external antenna.

Deploying the Platform with an Environmental Sensor

The environmental sensor chosen for test deployment was TE Connectivity’s MS8607 which measures pressure, temperature, and humidity. TE has a Grove MS8607 evaluation board which made it very easy to interface to the sensor evaluation platform. Complete project details, including application source code, are documented in the Xbee3 Zigbee Outdoor MS8607 Pressure Temperature Humidity (PTH) Sensor project page located on Digi-Key’s eeWiki site. Figure 3 shows the electrical connections and wiring diagram interface between the sensor and Zigbee radio platform.

Figure 3: Xbee3 Outdoor Zigbee PHT Sensor Project - Electrical Connections and Wiring Diagram. (drawn using Digi-Key Scheme-it®)

The full BOM (Bill of Material) and project details are contained in the below Digi-Key Scheme-it® project.

In this test project, the sensor platform was deployed on the roof of Digi-Key Electronics' headquarters building. Figure 4 shows pressure, temperature and humidity data collected by the PTH Sensor in February 2020.

Figure 4: Pressure, Temperature, Humidity Data. (image source: Digi-Key Electronics)

Real-World Benefits of FOTA

After installing the sensor platform on the roof of our headquarters building I noticed the MS8607 temperature data did not correlate with a different manufacturer’s sensor operating in the same environment. When previously tested at my desk at room temperature both sensors had similar readings but when installed outdoors there was a significant difference at cold temperature. After reviewing the datasheet, I realized I had not implemented the secondary low temp correction formula in the MicroPython application code. Since Digi Zigbee Xbee3 modules support firmware and application file system FOTA, I was able to correct and update my application code remotely over the air from the comfort of my desk. I didn’t have to trudge through the snow to retrieve the sensor platform and bring it back inside for reprogramming. FOTA allows a user to remotely update both the radio firmware and Micropython application from another Zigbee node in the same network. Information on implementing Xbee3 FOTA and a working example is found in the eeWiki project Xbee3 Firmware Over The Air (FOTA) update using XCTU.

Conclusion

Digi’s Xbee3 wireless Zigbee modules performed well as the intelligent controller for the Sensor Evaluation Platform. The platform is flexible and easy to modify for different sensors and update in the field. Zigbee provides a robust wireless network for sensor data that is easily expandable.

About this author

Image of Scott Raeker

Scott Raeker, Technical Marketing Manager at Digi-Key Electronics, has been with the company since 2006. He has over 35 years of experience in the electronics industry and holds an Electrical Engineering degree from the University of Minnesota. In his spare time, Scott enjoys the outdoors of Northwest Minnesota and working on his turn-of-the-century farmhouse.

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