A novel sensor-bridge-to-microcontroller interface

Abstract

-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.

Hardware and Software Implementation Aspects for Low-cost Multi-Channel Interface for Passive Resistive Sensors

“…Generally, the sensor interfaces can be divided in two groups: ones based on AD conversion that utilize analog-todigital converters (ADC) [5], and other based on relaxation oscillators (multivibrators) [6] and time-to-digital (TD) [7] or frequency-to-digital (FD) [8] conversion. The second approach can be sometimes advantageous, especially when the sensors are directly interfaced to a digital programmable device (such as microcontrollers) [9]- [11]. Microcontrollers usually include peripherals for accurate measurement of time events, which can be used for TD or FD sensor interfacing without the need of ADC.…”

Implementation of high-resolution time-to-digital converter in 8-bit microcontrollers

“…II we will present a new time stretching idea that can be implemented in a microcontroller with only a few passive external components. This idea is based on the "direct sensor-to-controller" [12][13][14][15][16][17][18] and "direct analog-to-controller" 19 techniques and therefore these techniques are introduced first.…”