Application Enhancements
It is always useful to consider how an application design could be improved, even if it is ultimately decided that the design effort or extra hardware costs are not justified by the improved performance. As mentioned above, the PWM module could be used to control the speed of the fan. The display could be upgraded to an alphanumeric LCD, so that more information could be displayed and the operating parameters shown to a greater degree of precision. A serial communication port could send the temperature data to a master controller, and receive new operating parameters. If a PC were acting as the host, an external USART/ USB converter would be needed. The PC could display the operating data, perhaps in graphical form, or as a plot of temperature variation over time. This data could then be saved on disk, and sent via a network to a supervisory system.
Other references on interfacing which cover the range of techniques needed for input and output in more detail include Interfacing PIC Microcontrollers: Embedded Design on Interactive Simulation by the author (Newnes 2006).
Simplified Temperature Controllers
We will now briefly look at using a couple of other chips to create simplified versions of the temperature controller.