Direct sensor-to-microcontroller is a simple approach for direct interface of passive modulating sensors to a microcontroller without any active components in between the sensor and the microcontroller and without an analog to digital converter. The metrological performances of such interface circuits are limited by certain microcontroller parameters which are predetermined by the manufacturing technology. These limitations can be improved by specific hardware-related techniques and can improve the accuracy, speed and resolution of the measurements. Such hardware solutions as well as proper selection of the electrical components are addressed in this paper. It has been shown that employment of only a few MOSFET transistors can reduce the maximal relative error of single point calibration more than fifteen times and can increase the measuring speed around 30 % in all calibration techniques in the measurement range of PT1000 resistive temperature sensors. Moreover, the effective number of resolution bits increases by more than 1.3 bits when using an external comparator.
In this paper the design and implementation of a plug-and-play analog resistance temperature sensor is presented. The smart temperature sensor consists of an analog sensor element with transducer electronic data sheet (TEDS) memory device and a network- capable application processor (NCAP) connected through a mixedmode interface (MMI). The mixed-mode interface and NCAP front-end electronic support have been implemented by the use of a standard 8-bit microcontroller. NCAP's application processing and network communication functions are implemented based on the concept of virtual instrumentation using a PC. The implemented NCAP can also be used as a plug-and-play stand-alone data acquisition system or as development system for plug-and-play sensors compliant with the IEEE 1451.4 standard. Details of sensor implementation and test results are included in the paper.