Accuracy of NTC Thermistor Measurements Using the Sensor to Microcontroller Direct Interface

Portable and wearable sensor systems are usually based on microcontrollers or Field Program-mable Gate Arrays (FPGAs), where the sensors are measured using an analog-to-digital converter (ADC). An alternative solution, with benefits in terms of cost reduction and lower power con-sumption, is the sensor-to-microcontroller direct interface (SMDI), a technique where the sensor is measured using the general purpose input output (GPIO) interface present on any microcon-troller or FPGA. In this paper, the measurement accuracy of a non-linear temperature sensor (NTC 3950) using SMDI was evaluated by means of LTSpice simulations in the temperature range from −10 °C to 80 °C. The temperature was estimated using two different models and the results have shown that the most accurate model (Steinhart-Hart model) achieves an average tempera-ture error of 0.078 °C.