Sensing real world parameters like temperature is always fun. This is why temperature sensing projects keep coming and coming. This is really great as there are tons of different temperature sensors around ant they are different in their connection interface and accuracy. In current project there is a TMP275 digital temperature sensor used that is 0.5 °C accurate and uses Two-Wire interface to connect to microcontroller. It has common range like other semiconductor sensors have – that is from -40°C to 125°C.
The other part is pretty standard solution. There is an ATmega8 microcontroller used that reads sensor data and displays it on 4 digit 7 segment LED indicator. It has a 7805 voltage regulator on board so it can be powered from a standard 9V battery. Project is well documented and commented. I’d say this is pretty nice digital thermometer which does what it supposes to do – it shows ambient temperature.