Sifuentes E; Cota-Ruiz J; González-Landaeta R

Language: English
References: 20
Page: 91-99
PDF size: 0. Kb.

ABSTRACT

This paper proposes a system that converts a time-modulated signal from a resistive sensor into a digital signalwith the goal to estimate the respiratory rate of a subject. To detect breathing, a known method based on a nasalthermistor, which detects temperature changes near the nostrils, is used. In this work, the thermistor mountedin a Wheatstone bridge, forms a RC circuit which is connected directly to a microcontroller, without using anyanalog circuit or analog-digital converter. Thus, whenever the subject breathes, it causes a fractional change inresistance x( ΔR/R0) on the thermistor, and this produces a time-modulated signal that is directly digitized withthe microcontroller. Measurements were made on 23 volunteers, obtaining changes ofx ›0.01. The temperatureresolution was 0.2^◦C, and the time response was 0.8 s, mainly limited by the thermistor properties; these featureswere enough to obtain a well-defined waveform of the breathing, from which was easy to estimate the respiratoryrate by a compact, low cost and low power consumption system. Unlike interface circuits based on voltage or currentamplitude, with this kind of interface, the self-heating of the sensor is avoided since the thermistor does not requireany voltage or bias current.

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