A Combination of Astable Multivibrator and Microcontroller for Thermistor-Based Temperature Measurement Over Internet

The paper reports the development of a cost-effective Negative Temperature Coefficient thermistor-based temperature transducer for embedded systems and for the Internet of Things applications. The venture uses a 555 timer-based astable multivibrator as a first-stage linearizer in which the thermistor and a linearizing resistance in series with it modulate the threshold voltages of the internal comparators of the integrated circuit. The output is further processed by a microcontroller which performs a second stage linearization with the help of a look-up table coupled with linear interpolation. Furthermore, the microcontroller uses an Ethernet shield to transmit the temperature information to remote locations. The performance of the proposed setup has been examined for three different thermistors, over 30 °C to 120 °C. The measurement strategy has been found to outperform the competing arrangements reported in recent times, with regard to the measurement accuracy, linearity of transfer, compactness, cost, reliability, and immunity to drift.