Temperature sensors are very important in many projects especially in temperature logging devices and alarms. In this article we are going to design a digital thermometer using Arduino Uno. This digital thermometer is built around the LM35 which is a precision integrated-circuit temperature sensor whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. Its output changes by 10 mV per °C so there is no need for calibration. It can measure a wide range of temperature from −55 to +150°C