Abstract-Error analysis of a resistive sensor-to-microcontroller interface based on pulse-width modulation and time-ratio measurement shows that internal input and output resistances in microcontroller digital ports produce zero, gain and nonlinearity errors. The time-ratio measurement technique cancels these errors when the sensor resistance equals the reference resistor and reduces errors around that point. We propose two simple methods of reducing those errors for sensors with a wide dynamic range. Both methods use time-ratio measurements. The first method uses several reference resistors covering the sensor resistance range; the second method uses two-point calibration. The second method is more efficient and yields errors that can be smaller than 0.5 for a sensor resistance from about 600 to 3550 .Index Terms-Error analysis, error reduction, microcontroller interface, resistive sensor, sensor interface, time-ratio measurement.
No abstract
Abstract-Error analysis of a resistive sensor-to-microcontroller interface based on pulse-width modulation and time-ratio measurement shows that internal input and output resistances in microcontroller digital ports produce zero, gain and nonlinearity errors. The time-ratio measurement technique cancels these errors when the sensor resistance equals the reference resistor and reduces errors around that point. We propose two simple methods of reducing those errors for sensors with a wide dynamic range. Both methods use time-ratio measurements. The first method uses several reference resistors covering the sensor resistance range; the second method uses two-point calibration. The second method is more efficient and yields errors that can be smaller than 0.5 for a sensor resistance from about 600 to 3550 .Index Terms-Error analysis, error reduction, microcontroller interface, resistive sensor, sensor interface, time-ratio measurement.
-Sensor bridges are usually interfaced to microcontrollers by supplying the bridge with a voltage or current and digitizing the resulting voltage or current after being amplified and low-pass filtered. This paper proposes an alternative method to interface a sensor bridge to a microcontroller that does not need any active component between the bridge and the microcontroller. The bridge is considered a network with three inputs and one output. The resistance of each input to the output depends on the measurand. Using each input in turn to charge a capacitor connected to the bridge output yields three different time intervals. For a full bridge (a sensor at each arm), the ratio between the difference between two time intervals and the third time interval yields the fractional resistance change. Two-point calibration reduces zero and gain errors attributable to the electrical parameters of the ports of the microcontroller. The absolute error for a 15 psi (103.4 kPa) pressure sensor with 5000 Ω Ω Ω Ω arms and a full-scale output of 125 mV is below 0.05 % of full scale, which is better than 1 LSB for an 11 bit ADC.
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