Firestone manufactures Dragon Bench, a heated outdoor seat intended as an energy-efficient replacement for patio heaters outside bars and restaurants.

CEL had already designed a simple thermostat to regulate the temperature of these heated bench seats, and so was the natural choice when Firestone wanted to upgrade the system to permit centralised monitoring and control of multiple units from a single location. Their requirement was to have a device behind the bar which would be able to set and show the temperatures of all the heaters, turn them on in time for dinner service and off at the closing time, and indicate any faults that required attention.

Working together with software engineers at Firestone, CEL developed a smart thermostat around a Zigbee wireless network. The Zigbee standard was chosen because it forms a ‘mesh’ network, in which any device can communicate with any other by automatically routing traffic via intermediate devices. This would mean that benches could be spread over a large commercial outdoor space with no need to have all of them within the radio range of the bar.

With an eye on ensuring the system remained trouble-free and reliable, features were included to secure it from unwanted radio interference, whether benign, malicious or just a nearby neighbour with the same kit.

For simpler installations with only a few benches, the CEL thermostat also included an LCD display, buttons and a real-time clock, so it could be programmed to switch on and off at different times according to a weekly schedule. The option was provided to omit the wireless module on these units to save manufacturing cost.

The finished product was a true collaboration between Firestone and CEL, with CEL providing electrical design, specifications and firmware, and Firestone taking care of the mechanical design, the central controller and the heated benches themselves.

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