Countertop cooking appliances, such as electric ranges and skillets, use an adjustable thermostat to vary the heat output. In traditional appliances, a mechanical thermostat was used in series with the heating element to control the current through the element. While this technique is inexpensive, it is less accurate and less reliable over time because the mechanical components wear out. This application note from Microchip describes a low-cost microcontroller-based design which eliminates these drawbacks. The solution uses the PIC10F204 microcontroller, which gathers user inputs from a potentiometer and control current to the heating element via a triac. The application note also discusses triac theory in brief. Power supply for the PICmicro is derived directly from the AC lines using a zener diode and resistors. The design also implements two additional features: (1) a status LED indicating the range is on or off, and (2) a safety feature that automatically shuts the range after 2 hours if it is left unattended.
Low-cost thermostat solution for electric range
