Described herein is a an optical sensing unit, the optical sensing unit including a one-dimensional array of sensor locations, each sensor location being responsive to an incident optical signal to generate a local analog intensity value representative of the intensity of the optical signal at the sensor location, the sensing unit including a digital interface to deliver a local digital intensity value corresponding to the local analog intensity value, a first microcontroller function in communication with the digital interface for sequentially collecting local digital intensity values to form a group of digital intensity values corresponding to an intensity variation across the array over a predetermined sensing period, a second microcontroller function cooperating with the first microcontroller function to receive the group of digital intensity values for transfer to an output device.