How’s the temperature today? Cold, good or hot? Ambient temperature can be easily measured without any special temperature sensor. You just need… a common diode! Well, actually, a diode and a resistor. Diodes change their forward voltage drop at a rate of approximately -2.3 mV per degree Celsius (ºC), so we just need to measure that voltage.
You may want to start by reading Setting up a LED bargraph. Check also our other Free Articles.