Loading-effects reduction using a voltmeter in series and an ammeter in parallel

This article proposes a method for reducing the loading effects when a dc voltage or current is measured in a linear circuit with a digital multimeter (DMM). In the proposed method, the voltmeter is placed in series to estimate the current, and the ammeter is placed in parallel to estimate the voltage, which is the opposite of the conventional approach. Its application is particularly of interest when the equivalent resistance between the nodes of the dc voltage (current) under measurement is high (low). In comparison with the conventional method, the relative error is up to a factor of 10 4 lower if the equivalent resistance equals the shunt (input) resistance of the DMM when a dc current (voltage) is measuredPostprint (author's final draft

Toward non-CPU activity in low-power MCU-Based measurement systems

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksThis article evaluates the benefits of having peripheral-triggered peripherals in a microcontroller unit (MCU) intended for low-power sensor applications. In such an architecture, the functionality is moved from the central processing unit (CPU) to the peripherals so that a peripheral is able to trigger another peripheral with non-CPU intervention. For the sensor data logging application under study, both energy consumption and measuring time are reduced by a factor of 2 with respect to the case of applying an interrupt-based approach that requires the CPU intervention.Peer ReviewedPostprint (author's final draft

A tutorial on thermal sensors in the 200th anniversary of the seebeck effect

Two noteworthy events associated to the physics of thermal sensors were demonstrated and announced in 1821, exactly two hundred years ago. The first event was the Seebeck effect, which led to the development of thermocouples. The second was the study of the thermal dependence of the resistivity of pure metals, which led to the design of resistance temperature detectors (RTD).Postprint (updated version

A microcontroller-based interface circuit for non-linear resistive sensors

This article proposes a circuit based on a microcontroller unit (MCU) for the direct measurement and linearization of non-linear resistive sensors, such as thermistors. The measurement relies on an embedded digital timer and does not require (either embedded or external) operational amplifiers or an analog-to-digital converter, thus resulting in a low-cost, low-power design solution. The circuit includes a known resistor with a twofold function: it is a reference for circuit auto-calibration purposes, and it is in parallel with the non-linear resistive sensor for linearization purposes.Postprint (updated version

Rail-to-Rail Timer-Based Demodulator for AM Sensor Signals

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper proposes a novel timer-based demodulator for low-frequency amplitude-modulated (AM) sensor signals with a rail-to-rail operating range. The demodulator extracts the amplitude of the AM signal by measuring the period of a reference signal that is altered by the AM signal itself, as already suggested in a previous paper. The rail-to-rail operation, which is the main contribution of the novel circuit, is achieved by simply but cleverly incorporating a multiplexer that enables the comparison between the two signals (reference and AM) just at the beginning and at the end of the period measurement. This new topology offers an operating range that is up to more than four times wider than that reported in the literature. The input-output characteristic in such a wider operating range is not linear, but it can be accurately modeled by a second-degree polynomial.Peer ReviewedPostprint (author's final draft

Nodal and mesh analysis simplification by introducing a theorem-based preliminary step

This brief proposes a new and simplified method for the analysis of linear circuits that combines the classical mesh-current or node-voltage method with a recently-stated theorem. The beforehand application of such a theorem, which involves the insertion of an open or short circuit, in a circuit with N meshes or nodes results in a system of N- 1 linear equations for N- 1 unknowns, instead of N equations for N unknowns obtained using the conventional approach. Therefore, if the circuit is analyzed in matrix form, the resulting coefficient matrix is square of order N- 1, instead of N , thus facilitating the hand calculations. Examples of circuit analysis are provided to demonstrate the applicability and advantages of the proposed analysis method in comparison with the conventional approach.Peer ReviewedPostprint (published version

A microcontroller-based interface circuit for three-wire connected resistive sensors

This article proposes and experimentally characterizes a novel microcontroller-based interface circuit to read three-wire connected resistive sensors, which are quite common in industrial applications to measure, for instance, temperature. The circuit relies on measuring, via an embedded digital timer, four discharging times corresponding to four different RC circuits, which include the sensor resistance and the parasitic resistance of the wires. A prototype has been built with a commercial microcontroller measuring resistances that correspond to a Pt100 thermal sensor and with different values of wire resistance. According to the experimental results, the error, with respect to the case with null wire resistances, is lower than 25 mO for a 5-m interconnecting cable. In addition, the non-linearity error (NLE) is lower than 0.02%–0.03% full-scale span (FSS), regardless of the wire resistances and also of any potential mismatch between them.Peer ReviewedPostprint (published version

Improving the efficiency of PV low-power processing circuits by selecting an optimal inductor current of the DC/DC converter

In the context of autonomous sensors powered by small-size photovoltaic (PV) panels, this work analyses how the efficiency of DC/DC-converter-based power processing circuits can be improved by an appropriate selection of the inductor current that transfers the energy from the PV panel to a storage unit. Each component of power losses (fixed, conduction and switching losses) involved in the DC/DC converter specifically depends on the average inductor current so that there is an optimal value of this current that causes minimal losses and, hence, maximum efficiency. Such an idea has been tested experimentally using two commercial DC/DC converters whose average inductor current is adjustable. Experimental results show that the efficiency can be improved up to 12% by selecting an optimal value of that current, which is around 300-350 mA for such DC/DC converters.Peer ReviewedPostprint (published version

Demodulating AM square signals via a digital timer for sensor applications

This paper evaluates theoretically and experimentally the performance of a timer-based demodulator applied to low-frequency amplitude-modulated (AM) square signals coming from sensor circuits. The demodulator extracts the amplitude of the AM square signal by measuring the period of a reference triangular signal that is altered by the AM signal itself, as already suggested in a previous paper but for AM sinusoidal signals.Postprint (published version

Experimental study on the power consumption of timers embedded into microcontrollers

An experimental study on the current consumption of timers embedded into microcontrollers is presented in this work. The study is carried out in two commercial microcontrollers (MSP430FR5969 and ATtiny2313) and the experimental results are co mpared with the scarce data provided in their datasheets. The sensitivity (expressed in ¿A/MHz) reported in the datasheet seems to be only applicable if the frequency divider of the timer equals one. Otherwise, such a sensitivity is lower but there is a significant offset component, leading to a higher power consumption at the same operating frequency. The knowledge extracted from this work is expected to provide guidelines to better use embedded timers in low-power sensor applicationsPostprint (updated version