Temperature controllers a used in many areas. Heating systems, storage facilities, greenhouse and many more use them. Most of them work in similar way – it measures temperature and compares to one or many threshold values. If it exceeds one then alarm is raised or action is taken like window closing motor turned on or heater switched on.
It is best to start building an universal temperature controller which could fit in many areas. Shawon suggests an Atmega32L based temperature controller which gives some flexibility by adjusting some settings to fit your needs. It has an audio alarm. High and low threshold setting, time based settings. Settings are backed up in internal EEPROM. Controller displays status mesasges and current temperature value on standard 20×4 LCD. Temperature values are captured from LM35 sensor using ADC0 channel of AVR MCU. There are four push buttons to navigate menu and four status LEDs to give additional indication which may be useful when inspecting from a distance.