A controller for a touch-screen sensor is described. The controller comprises a voltage generator for generating a first voltage signal and at least one output for outputting the first voltage signal such that the first voltage is applied across a resistive layer of the sensor in a first direction (e.g. X direction). The controller further comprises an input for receiving a second voltage signal representing the voltage on the resistive layer measured at a touch position by a measuring electrode of the sensor when the sensor is touched. A processor determines the co-ordinate in the first direction (e.g. X co-ordinate) of the touch position using the second voltage signal received during a first measuring period. Specifically, the co-ordinate is determined by determining the attenuation of the first voltage signal in the second voltage signal. The first voltage signal is generated such that the first voltage applied across the resistive layer is a time-varying voltage during the first measuring period, having at least one known characteristic. In one embodiment, voltages are applied across the resistive layer in two directions (e.g. X and Y directions) simultaneously, allowing the processor to determine the X and Y co-ordinates simultaneously.