This project shows the temperature on a three digit 7-segment display, it measures the temperature from -9.5 to 99 degrees Celcius in 0.5 C steps, or from 0 to 210 degrees Fahrenheit in 1.0 degrees steps. Because of the LED display the temperature is also readable in the dark.
The TCN75 from MicroChip is used to measure the temperature. The TCN75 has a 2 wire serial interface, which is a bidirectional bus with a speed up to 400Kbs. Up to eight devices of the same type can be controlled by the bus. In this case only one device is connected to the ATTiny2313 microcontroller. The 2 wire bus is also called I2C, this name is proprietery to the Philips Electronics company. I2C is a abbreviation for IC Inter Circuit. The TCN75 has also a build in programmable thermostat, which is not used in this circuit.
The ATTiny2313 is used the control the two wire serial interfacing with the TCN75 and to translate the information for showing on the three digit 7-sement display. The reading of the temperature from the DS1621 happens every 3 seconds. A ceramic resonator is used for clocking the microcontroller.