User`s manual

DemoKit-LG2 User’s Manual
16
internal interrupt is generated. The capture value is read using this interrupt. In the next step, the C18
capacity will be discharged again. The same procedure starts once more with port P03. This time the
capacitor is charged via the unknown resistor R
VAR of the temperature sensor and after the threshold is
reached again the second timer value is read out.
The unknown R
VAR, and consequently the resistor value of the temperature sensor, can be calculated
from the two values obtained using the method described earlier.
R REF : R 6 = V CREF = V DD 1 - e
t REF
R REF x C
-
R
VAR : R 5 + R T = V CREF = V DD 1 - e
t VAR
R VAR x C
-
V
C = V CVAR = V CREF = const
The threshold level of the Schmitt-trigger input does not have any influence on the accuracy of the
measurement, as this will be a constant for both measurements.