The SMT172 is a ultra-low power, high accuracy temperature sensor. The output signal is pulse width modulated (PWM) and the duty cycle is a function of the measured temperature. For more details see the home page of the manufacturer: http://smartec-sensors.com/ and the documentation. Accuracy can be up to 0.1 degree Celsius for a limited temperature range and the resolution up to 0.001 degree Celsius.
With a 16MHz CPU and a conversion time of 30 ms a resolution of about 0.01 degree Celsius can be reached.
This library uses Timer1, Timer4 or Timer5 and ICP1, ICP4 or ICP5.
The SMT172 needs a clean powersupply (a 100uF capacitor with a 100 nF ceramic capacitor in parallel fed through a small signal diode), a 220 ohm resistor in series and a 100nF ceramic capacitor as close to the sensor as possible. See also the diagram in the extras folder.