Apparatus comprising: a host controller for controlling operating functions of the apparatus, a touch panel module comprising a touch panel sensor element providing a surface, defined by an array of electrodes arranged on a substrate, within which the presence of an adjacent object is to be detected; a proximity capacitance measurement circuit for determining the presence of an object approaching the sensor element of the touch panel module, and a power supply circuit for providing power to the host controller, the touch panel module and the proximity capacitance measurement circuit on respective power supply lines; wherein the touch panel module comprises the touch panel sensor element and a touch panel controller configured to measure an indication of a capacitance characteristic associated with an array of sensor electrodes comprising the touch panel sensor element, and to generate corresponding touch panel output signalling in response thereto, and to communicate the touch panel output signalling to the host controller via a touch panel output channel (219; 218); wherein the proximity capacitance measurement circuit comprises a capacitance measurement channel coupled to a ground power supply line connected to the touch panel module and configured to measure an indication of a capacitance characteristic associated with the ground power supply line to which the proximity capacitance measurement circuit is coupled, and to generate corresponding proximity capacitance measurement circuit output signalling in response thereto, and to communicate the proximity capacitance measurement circuit output signalling to the host controller via a proximity capacitance measurement circuit output channel; and wherein the touch panel power supply at the touch panel module is galvanically isolated from the proximity capacitance measurement circuit power supply at the proximity capacitance measurement circuit. a host controller for controlling operating functions of the apparatus, a touch panel module comprising a touch panel sensor element providing a surface, defined by an array of electrodes arranged on a substrate, within which the presence of an adjacent object is to be detected; a proximity capacitance measurement circuit for determining the presence of an object approaching the sensor element of the touch panel module, and a power supply circuit for providing power to the host controller, the touch panel module and the proximity capacitance measurement circuit on respective power supply lines; wherein the touch panel module comprises the touch panel sensor element and a touch panel controller configured to measure an indication of a capacitance characteristic associated with an array of sensor electrodes comprising the touch panel sensor element, and to generate corresponding touch panel output signalling in response thereto, and to communicate the touch panel output signalling to the host controller via a touch panel output channel (219; 218); wherein the proximity capacitance measurement circuit comprises a capacitance measurement channel coupled to a ground power supply line connected to the touch panel module and configured to measure an indication of a capacitance characteristic associated with the ground power supply line to which the proximity capacitance measurement circuit is coupled, and to generate corresponding proximity capacitance measurement circuit output signalling in response thereto, and to communicate the proximity capacitance measurement circuit output signalling to the host controller via a proximity capacitance measurement circuit output channel; and wherein the touch panel power supply at the touch panel module is galvanically isolated from the proximity capacitance measurement circuit power supply at the proximity capacitance measurement circuit.