Folks - I've lifted this 'sidebar' about our Plexus IoT development story from an application note I'm writing about powering IoT devices using solar energy.
We named the product (in the photos above) - after the 'Solar Plexus' in the human body - two puns intended - is a mesh network delivering data from across the farm (where cellular access is not always present or reliable) via 2.4 GHz ZigBee radio.
Hope you enjoy the story
Andrew (at MEA)
‘Plexus’ - an On-farm Internet of Things
Designing and operating an ‘Internet of Things’ on-farm requires a multi-disciplinary approach to product development involving electronics, firmware, software, mechanical engineering and industrial design, web design, communications engineering, manufacturing skills, good field people and a deep understanding of just how tough an environment it really is when trying to keep measurement technology running year-round for a decade despite the hazards of weather, farm machinery and the occasional rogue human. That we came into this business with thirty years of data-logging experience and environmental measurements helped, but we needed to learn new skills on all fronts to pull this off, innovating our business model as we switched from a custom engineering base to that of a manufacturer.
Driving this development was a sense that the old days of storing data in data loggers - then unloading it the farm computer - were at an end, and that modern farmers needed access to their sensor data at any time and from anywhere. This required the power of the Internet to move, store and present this data on PCs, tablets and smart phones without any proprietary software in the mix. It was a new world. Data needed to be collected using energy gathered on-site, ‘hopped’ by cooperative radios across the property to some master controller then automatically fed via a modem to an Internet server that would store data and serve it up to the farmer whenever he logged in. Temporary data storage was needed all along the chain to patch over the usual in-field outages, automatically playing catch-up when network elements were restored.
The IEEE 804.15.4 ‘ZigBee’ standard was the obvious starting place to develop such technology because of the deep underpinning developed by the standards people and implemented by big IC manufacturers who made radio systems-on-chip, including the internal software ‘stacks’ that operate the various layers of networked radios. This created an immediate problem for the development team, as each node on the Plexus on-farm network needed to be a ‘router’ under the design brief, forwarding data across a self-healing mesh network with the minimum of set up fuss. However, ZigBee routers are typically ‘always on’, and the solar-powered energy budget simply did not allow for this. The eventual compromise was to re-fashion the whole network for a solid minute every fifteen minutes, then go into complete power-down mode for the remaining 14 minutes to conserve energy.
Plexus systems guarantee a maximum 1000 m spacing between any field station in flat country. Given a 5-deep parent-child router arrangement, this allows coverage of most on-farm applications up to 1000 hectares. Radios, solar panels and batteries have to be light-weight and streamlined to live safely about two metres above the top of the crop for clean solar and radio access. Over-row machinery in permanent row crops such as grapes means that the whole Plexus field station pod needs to be ‘knock-down-spring-back’ so that on-farm operations are unaffected by the presence of the radio system. All this geometrical confinement forces a limit on the energy budget that is physical; it only becomes possible if the solar panel is small and light enough to fit inside a tough polycarbonate streamlined enclosure. 5V 400mW solar panels measuring 50m x 50mm fitted the bill but limit field station average operating current to a maximum of 8 mA, distributed between radio, sensor and system elements.
Plexus product development took over three years of intensive effort, including seemingly endless returns to the field to be beaten up and humiliated yet again as we tried to understand what was going on – or was not. All this before we even let customers near the data that was being produced. The usual engineering compromises were reached in an effort to meet the deadlines imposed on us by the need to get to market and get a return on investment. Needless to say, we are still unwinding some of these ‘frozen-in-stone’ decisions in an effort to build a more flexible system capable of handling sensors and systems we’ve not even heard of yet. Yet the original concepts proved robust, and more than two years of field data from hundreds of sites across a broad range of crops and climates has vindicated the design decisions made.
Like all new game-changing technologies, the Internet of Things is in danger of being over-hyped. Yet it can be made to work by a highly disciplined and experienced engineering team, given sufficient focus and across-company support. But it’s not a game for the faint-hearted or the weak-of-purse.