Improved Direct Interface Circuit for Resistive Full-and Half-Bridge Sensors

Resistive bridge sensors can be directly connected to a microcontroller by using time-based measurement circuits that yield a digital output proportional to the fractional resistance change. However, internal resistances (R_ini) of microcontroller pins result in systematic errors. We propose an improved measurement circuit and two time-based equations to compensate for R_ini. The proposed circuit and equations have been tested on full- and half-bridge circuits. For both types of bridge, the improved interface circuit and the two novel algorithms reduce the maximal error by a factor greater than two.