case study page

CEL was contacted by Reventec Ltd, a manufacturer of sensors which are used by the professional motor racing industry, as well as in other applications which demand high reliability at elevated temperatures and under severe vibration.

Reventec was looking to produce a strain gauge with a 0 to 5V output for measuring the torque applied to the steering column of a racing car. Previously they had been buying in an amplifier from a third party, but it was quite expensive, too large, and required adjustment using a screwdriver which meant it could not be fully encapsulated to protect it from vibration.

CEL designed a prototype circuit around the Analog Devices AD8557 digitally programmable amplifier IC. This device can be programmed to adjust its gain and offset without the need for a physical potentiometer. To control this device and allow it to be adjusted easily, CEL developed software for a Microchip PIC which presented a simple command line interface that could be used via terminal software on any laptop.

The CEL software included a self-calibration facility, so the previously time consuming and fiddly process of adjusting out the zero offset was replaced by a single command taking just moments to execute.

The hardware was first prototyped on stripboard, allowing it to be debugged and demonstrated before committing to a PCB. Finally the board was laid out and sent off for manufacture, with the final design being just 18x25mm.

As well as all the CAD data and source code, Reventec was provided with full documentation describing how the board works, how to connect it up, and how to adjust the gain and offset for any given application using the serial interface.

In this case a clear understanding of the needs of the application resulted in a simple, inexpensive PCB which was quicker to assemble into a finished sensor than an off-the-shelf board, as well as being more robust, accurate and versatile.

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.