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Thermostat Family Software Architecture

Developed For: RiteTemp

Key Technologies:
Microprocessor: Microchip PIC24FJ128 (high-end product) and Microchip PIC18 (low-end product)
Device Bay: two pluggable BlueTooth Modules
Battery: Two AA batteries for power-backup

The Problem: 
Develop a firmware architecture and master implementation that will allow rapid development of a family of thermostat products. The high-end device has a bit-mapped graphics display and can control several stages of heating and cooling as well as a humidifier, dehumidifier and fresh-air baffle. The low-end device handles one stage of heating and cooling and has a simple multi-segment LCD. The code should require only simple re-compilation to change from any device in the family from low-end to high-end.

The Solution: 
CoAutomation worked with TechEn and acted as an advisor in the creation of the first implementation of the high-end thermostat hardware.

The client strongly desired that one Master Application Source would support the entire family of thermostats from low-end to high-end and still allow for precise control of available hardware resources. The high-end thermostat would support muliple stages of heating and cooling such as a two-stage heat pump with an oil-burner backup. The high-end thermostat could also control both an external humidifier and dehumidifier as well as a "Fresh Air" Vent. Many of the anticipated thermostat models would have pluggable modules for BlueTooth Radios.

The possibility of supporting so many different combinations of hardware resources required a firmware architecture that supported the "insertion" or "removal" of indvidual code modules without the need to modify code. CoAutomation specified and implemented a "software bus" that allowed modules to "post" data instead of using procedure calls or having a large area of global variables. This "bus" supported distribution of the data amoung the code modules that were present in each thermostat model. Because of the range of microcontroller performance in the thermostat family, the "software bus" required few resouces, yet was very flexible.

CoAutomation also assisted TechEn in adopting the Microchip graphics architecture to this project and guided development of the graphics code.

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