Digital readout circuit with direct microcontroller interface for bridge-connected resistive sensors

Resistive sensors in bridge configuration are common in the field of instrumentation. A digitizer circuit that works on the principle of capacitor charge-discharge is proposed in this paper. A direct digital readout is obtained by measuring the charge and discharge time intervals. The proposed converter is independent of circuit parameters like lead wire resistances, switch resistances and microcontroller pin resistances. The digitizer circuit provides the advantage of direct interface to microcontroller input-output ports and hence reduces the need for additional hardware. Simulation studies have been carried out for the proposed converter and the output is linear with worst case error within 0.005%. Results of hardware implementation of the digitizer circuit with fixed resistors emulating the behavior of bridge-network provided a linear output with worst case error within 0.1 %.