Temperature Controller Based on AVR

An AT90S2313 and a Dallas DS1621 Digital Thermometer to create a controller where the temperature is displayed on a dual 7-segment display while the parameters are set using the two buttons.

Using an I2C interface, the Dallas DS1621 chip interfaces the 2313. The I2C is a 2-wire bi-directional bus with a speed up to 400kbps. The same I2C bus can connect up to 8 DS1621 devices. The heating element is switched by a high current relay. The use of AVR 2313 is suitable for this task due to the right number of pins and makes things easier because it is programmable in C. the clocking of 2313 uses a 4MHz ceramic resonator.

Common cathode is used for the displays where the segments of both displays are tied together and the software handles the multiplexing. A single or double tap 9V transformer with a rectifier and a 5V regulator are used for the power supply making it straight forward. A drive voltage to the relay is supplied by the rectified input to the regulator.

A standard NPN transistor drives the relay that requires around 40-50mA. The relay should kick in using the two buttons.

Rest of the project