Direct microcontroller interface based digital readout circuit for single-element resistive sensors

A direct digitizer circuit suitable for resistive sensors is presented in this paper. The proposed converter works on the principle of time taken for charge-discharge cycles of a capacitor. The converter provides a digital output that is proportional to the measurand quantity of the single element resistive sensor, and is independent of circuit elements like line resistances, switch resistances or 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 0.01%. Results of hardware implementation of the digitizer circuit with fixed resistors emulating the behavior of resistive sensors provided a linear output with worst case error within 0.022%.