A modular position sensing system for sensing the position of a radiation blocking object in a sensing region, the system comprising: - a system controller; - a plurality of system modules coupled to the system controller, wherein the system modules at least partially enclose the sensing region, wherein the system modules include one or more radiation sources and one or more radiation sensors, wherein each radiation source is responsive to an emitter activation signal to emit radiation across at least part of the sensing region; and - a system communication bus configured to allow the system controller to communicate with each of the system modules, wherein: - each system module includes a module controller coupled to the system controller and wherein each module controller controls the operation of the system module in response to a control instruction received from the system controller, and - each radiation source may be activated independently and sequentially to emit radiation across at least part of the sensing region; and - wherein the system modules include at least one corner module including at least one corner radiation sensor and including the module controller, and wherein the corner radiation sensor is configured to report, to the module controller, an intensity level corresponding to the intensity of radiation incident on the corner radiation sensor from a plurality of the radiation sources, while each successive radiation source is independently activated, and characterized in that: - each system module includes one or more connectors (116, 117) for coupling to adjacent system modules, wherein the system communication bus includes the connectors between adjacent system modules; and/or - the system controller is coupled to at least some of the system modules through a wireless communication system. - a system controller; - a plurality of system modules coupled to the system controller, wherein the system modules at least partially enclose the sensing region, wherein the system modules include one or more radiation sources and one or more radiation sensors, wherein each radiation source is responsive to an emitter activation signal to emit radiation across at least part of the sensing region; and - a system communication bus configured to allow the system controller to communicate with each of the system modules, - each system module includes a module controller coupled to the system controller and wherein each module controller controls the operation of the system module in response to a control instruction received from the system controller, and - each radiation source may be activated independently and sequentially to emit radiation across at least part of the sensing region; and - wherein the system modules include at least one corner module including at least one corner radiation sensor and including the module controller, and wherein the corner radiation sensor is configured to report, to the module controller, an intensity level corresponding to the intensity of radiation incident on the corner radiation sensor from a plurality of the radiation sources, while each successive radiation source is independently activated, and characterized in that: - each system module includes one or more connectors (116, 117) for coupling to adjacent system modules, wherein the system communication bus includes the connectors between adjacent system modules; and/or - the system controller is coupled to at least some of the system modules through a wireless communication system. - each system module includes one or more connectors (116, 117) for coupling to adjacent system modules, wherein the system communication bus includes the connectors between adjacent system modules; and/or - the system controller is coupled to at least some of the system modules through a wireless communication system.