Temperature Sensor Circuit
 

This activity is a very simple example of using LEDs for measurement readouts.  In this circuit, a thermistor is used to measure the surrounding temperature.  If you put your fingers around the thermistor, you will cause the resistance of the thermistor which will in turn change the amount of voltage going to the LED.  That will cause the LED to either brighten or dim (depending on how the voltage is changed).    In this case, the LED is a visual measurement of the temperature. 

Activity (pdf)

Podcast (mp3