The temperature data acquisition systems available commercially present high costs and operational complexity to be applied in environment controlled agricultural buildings. The objective of this work was to propose, calibrate and validate a low cost electronic circuit for measuring temperature based on the frequency of an alternating voltage (0 to 5 V). The sensor connected to the circuit was a thermistor with resistance of 10 komega 25 ºC and negative temperature coefficient. The electronic circuit was connected to a computer using the parallel port and calibration was performed by comparing the thermistor to a standard liquid-in-glass thermometer. Regression analyses were performed on experimental data to obtain equations relating the frequency variation to resistance and resistance to temperature. The coefficients of determination showed excellent correlation among the variables (R² > 0.9999). Comparisons of the measurements obtained with the electronic circuit and two conventional data acquisition systems were carried out. The results demonstrated that the proposed circuit is capable to measure temperatures from 10 to 40 ºC with precision and accuracy.
data acquisition systems; temperature sensors; instrumentation
