A measurement method for lossy capacitive relative humidity sensors based on a direct sensor-to-microcontroller interface circuit

Z. Czaja MEASUREMENT – 2021
A new time-domain measurement method for determining the capacitance and resistance values of lossy relative humidity capacitive sensors is presented. The method is based on a direct sensor-to-microcontroller interface for microcontrollers with internal analog comparators and timers. The interface circuit consists only of four reference resistors (two reference resistors if a microcontroller includes a voltage reference source), a given sensor and a microcontroller. A systematic error correction algorithm based on a correction dictionary and the M-multiple measurement approach are also proposed in the paper. Experimental investigations were carried out using a prototype device based on an 8-bit ATXmega32A4 microcontroller. The experimental research confirmed that the relative errors of measurement of capacitance introduced by the interface circuit are less than 0.71% (for capacitance values 100 – 286 pF), and the relative errors of measurement of resistance are less than 0.74% (for resistance values 1 – 10 MOhm).

A measurement method for capacitive sensors based on a versatile direct sensor-to-microcontroller interface circuit

Z. Czaja MEASUREMENT – 2020
In the paper, there is presented a new time-domain measurement method for determining the capacitance values of capacitive sensors, dedicated, among others, to capacitive relative humidity sensors. The method is based on a versatile direct sensor-to-microcontroller interface for microcontrollers with internal analog comparators (ACs) and with precision voltage reference sources, e.g. digital-to-analog converters (DACs). The reference source can be replaced by a resistive divider attached to the negative input of the AC. The interface circuit consists only of a reference resistor Rr, a given capacitive sensor working as a voltage divider, and a microcontroller (its peripherals: AC, timer, DAC, I/O pins). A prototype of the proposed complete solution of a compact capacitive smart sensor based on an 8-bit ATXmega32A4 microcontroller has been developed and tested. The maximum possible relative inaccuracy of an indirectly measurable capacitance was analysed, and experimental research was also performed. The results confirmed that the relative errors of value determination for a capacitive sensor are less than ±0.06%, which corresponds to a capacitance measurement accuracy of less than 0.1 pF for a range of measured capacity values from 100 pF to 225 pF, which in turn corresponds to at least a 0.5% relative humidity resolution for commercial capacitive RH sensors (e.g. TE Connectivity HS1101LF and Philips H1).

A random signal generation method for microcontrollers with DACs

A new method of noise generation based on software implementation of a 7-bit LFSR based on a common polynomial PRBS7 using microcontrollers equipped with internal ADCs and DACs and a microcontroller noise generator structure are proposed in the paper. Two software applications implementing the method: written in ANSI C and based on the LUT technique and written in AVR Assembler are also proposed. In the method the ADC results are used to reseed the LFSR after its each full work cycle, what improves randomness of generated data, which results in a greater similarity of the generated random signal to white noise, what was confirmed by the results of experimental research. The noise generator uses only the internal devices of the microcontroller, hence the proposed solution does not introduce hardware redundancy to the system.

Time-domain measurement methods for R, L and C sensors based on aversatile direct sensor-to-microcontroller interface circuit

tIn the paper new time-domain measurement methods for determining values of resistive (R), inductive(L) and capacitive (C) sensors based on a versatile direct sensor-to-microcontroller interface for microcon-trollers with internal analog-to-digital converters (ADCs) and analog comparators (ACs) are presented.The interface circuit consists of a reference resistor Rrworking as a voltage divider, a given R, L or C sensorand a microcontroller (its peripherals: an ADC, an AC, a timer, I/O pins buffered by an inverter). A pro-totype of the proposed complete solution of a compact smart sensor based on an 8-bit microcontrollerhas been developed and tested. The maximum possible relative inaccuracy of an indirectly measurableresistance, inductance and capacitance were analysed. Also, experimental researches were made. Thefollowing relative errors of the sensor value determination were achieved: for the R sensor less than 3%,as well as very good results for the L sensor (less than 0.3%) and for the C sensor (less than 0.2%).

A compact smart sensor based on a neural classifier for objects modeled by Beaunier's model

A new solution of a smart microcontroller sensor based on a simple direct sensor-microcontroller interface for technical objects modeled by two-terminal networks and by the Beaunier’s model of anticorrosion coating is proposed. The tested object is stimulated by a square pulse and its time voltage response is sampled four times by the internal ADC of microcontroller. A neural classifier based on measurement data classifies the tested object to a given degradation stage.

A method of measuring RLC components for microcontroller systems

A new method of measuring RLC components for microcontroller systems dedicated to compact smart impedance sensors based on a direct sensor-microcontroller interface is presented. In the method this direct interface composed of a reference resistor connected in series with the tested sensor impedance is stimulated by a square wave generated by the microcontroller, and then its voltage response is sampled by an internal ADC of the microcontroller. The obtained set of voltage samples is used to determine values of the sensor model impedance components.

A method of self-testing of an analog circuit terminated by an ADC in electronic embedded systems controlled by microcontrollers

A new self-testing method of analog parts terminated by an ADC in electronic embedded systems controlled by microcontrollers is presented. It is based on a new fault diagnosis method based on on-line (i.e. during measurement), transformations of voltage samples of the time response of a tested part to a square pulse - onto localization curves placed in the measurement space. The method can be used for fault detection and single soft fault localization.

A testing method of analog parts of mixed-signal electronic systems equipped with the IEEE1149.1 test bus

A new solution of the JTAG BIST for testing analog circuits in mixed-signal electronic microsystems controlled by microcontrollers and equipped with the IEEE1149.1 bus is presented. It is based on a new fault diagnosis method in which an analog circuit is stimulated by a buffered signal from the TMS line, and the time response of the circuit to this signal is sampled by the ADC equipped with the JTAG. The method can be used for fault detection and single soft fault localization in an analog tested circuit (A testing method of analog parts of mixed-signal electronic systems equipped with the IEEE1149.1 test bus).

An Implementation of a Compact Smart Resistive Sensor Based on a Microcontroller with an Internal ADC

In the paper a new implementation of a compact smart resistive sensor based on a microcontroller with internal ADCs is proposed and analysed. The solution is based only on a (already existing in the system) microcontroller and a simple sensor interface circuit working as a voltage divider consisting of a reference resistor and the resistive sensor connected in parallel with an interference suppression capacitor. The measurement method is based on stimulation of the sensor interface circuit by a single square voltage pulse and on sampling the resulting voltage on the resistive sensor. The proposed solution is illustrated by a complete application of the compact smart resistive sensor used for temperature measurements, based on a 8-bit microcontroller ATxmega32A4 with a 12-bit ADC and a Pt100 resistive sensor. The results of experimental research confirm that the compact smart resistive sensor has 1 oC resolution of temperature measurement for the whole range of changes of measured temperatures.

A method of self-testing of analog circuits based on fully differential op-amps with theTCBF classifier

A new approach of self-testing of analog circuits based on fully differential op-amps of mixed-signal systems controlled by microcontrollers is presented. It consists of a measurement procedure and a fault diagnosis procedure. We measure voltage samples of a time response of a tested circuit on a stimulation of a unit step function given at the common-mode reference voltage input of the op-amp. The fault detection and fault localization is carried out by the TCBF neural network classifier.