Figure 1. NTC-thermistor
STK502 includes a two screw-terminal block where a sensor can be connected. The STK502 kit is shipped with a NTC-thermistor attached to this screw-terminal. A NTC-thermistor is characterised by the fact that when the temperature goes down the resistance goes up. Using a voltage divider and reading the voltage over the thermistor through the ADC-channels on ATmega169, the temperature can be calculated. A pplication note "AVR064: STK502 – A Temperature Monitoring System with LCD Output" describes the details of the application.