Circuit design and implementation for digital temperature&humidity measurement and control

This paper describes a mixed signal, low power circuit design for temperature and humidity measurement and control. Temperature and humidity are sensed using a thermistor sensor and a hygrometer sensor. The theory of RC oscillator is used to convert sensor resistance Into a frequency signal. A ROM(Read Only Memory) is used to map the schmitt trigger frequency onto temperature and humidity. The control block can control the outer device to implement some demand according to the value of measurement. This circuit can measure temperature to an accuracy of 1 degreesC in the range of -20degreesC to 60degreesC and measure humidity to an accuracy of 10%R-H in the range of 40%RH to 90%RH.