Smart sensor nodes cut costs in ubiquitous IoT data capture

June 22, 2018 Brandon Lewis

The Internet of Things is about optimizing systems, businesses, and quality of life through data. So, despite the importance of networking, the cloud, security, and many other IoT building blocks, it really comes down to sensors.

The more sensors deployed in a given application – be it building management, patient monitoring, data center leak detection, or even livestock tracking – the more opportunities companies have to identify trends, increase efficiency, and potentially create new revenue generating services.

Of course, sensors also come at a cost. Particularly in high-volume commercial and industrial IoT deployments, the expense of deploying sensors everywhere can quickly equal a negative return on investment. Add in the requisite connectivity, memory, compute, and other components of an IoT sensor node, and what you have is a non-starter for ubiquitous sensing.

However, the cost of IoT sensors is falling (Figure 1). So, too, is the overall cost of IoT sensor nodes.

Figure 1. According to GE, the average cost of IoT sensors is projected to drop to $0.38 by 2020. (Source: GE)

RF-enabled flex sensors bring ubiquitous data capture to IoT

Over the last couple of years, ON Semiconductor has been working on a technology called Smart Passive Sensors (SPS). SPS devices are battery-less, microcontroller-less RF sensor nodes that measure moisture or temperature, and can be manufactured in PCB, flexible PET, or foam-based form factors (Figure 2).

Figure 2. ON Semiconductor’s Smart Passive Sensors (SPS) are battery-less, microcontroller-less RF sensor tags.

Without a battery, SPS sensor tags use existing RF field to generate 30 dBm of power that it harvests for operation. Current-generation SPS tags include a memory block of a few hundred bytes for storing sensor values, and wireless transmit range of 1-2 m to 5-10 m depending on SKU. They operate in the FCC 902-928 MHz and ETSI 866-868 MHz frequency bands, and have a working temperature range of -40º C to +85 ºC.

Most importantly, at volume, select SPS sensor tags are available for around $1.

SPS tags pair with a UHF sensor hub based on a Raspberry Pi, which can be used for local processing or to relay sensor data to cloud databases through Ethernet, USB, and HDMI ports (Figure 3). The hubs support a read rate of 100 tags/second.

Figure 3. The SPS sensor hub is a UHF reader based on the Raspberry Pi with eight antenna ports and Ethernet, HDMI, and USB connectivity.

What’s next for low-cost sensing?

Doug Seitz, Product Marketing Manager for Smart Passive Sensors at ON Semiconductor, has seen SPS devices deployed in a range of applications, from building emergency control using temperature and moisture tags to hospital room monitoring with IV bag level checking and patient fall detection to livestock body temperature monitoring and location tracking.

In fact, the devices have garnered so much interest that ON Semi, who manufactures the SPS packages, plans to add additional capabilities in its next-generation sensor tags scheduled for release in the second half of 2018. These include additional sensor types, such as CO2 detection, water pressure, humidity, and even non-ON Semi-produced sensors, as well as support for connectivity technologies such as Bluetooth, Zibgee, and other sub-GHz communications protocols. Gen 2 SPS tags will also upgrade the on-device memory into the Kb range, and include battery support for applications with inconsistent exposure to an RF field.

Seitz says that new applications for SPS technology are emerging every week.

I say that this is an interesting venture from a component vendor into the “systems” realm.

About the Author

Brandon Lewis

Brandon Lewis, Editor-in-Chief of Embedded Computing Design, is responsible for guiding the property's content strategy, editorial direction, and engineering community engagement, which includes IoT Design, Automotive Embedded Systems, the Power Page, Industrial AI & Machine Learning, and other publications. As an experienced technical journalist, editor, and reporter with an aptitude for identifying key technologies, products, and market trends in the embedded technology sector, he enjoys covering topics that range from development kits and tools to cyber security and technology business models. Brandon received a BA in English Literature from Arizona State University, where he graduated cum laude. He can be reached by email at

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