Injection device comprising an optical sensor

An arrangement for determining the position of a dose setting member adapted to set a dose of a medicament to be injected from an injection device, the arrangement comprising:

• a rotatably mounted member having a plurality of optically coded tracks arranged on an outer surface thereof adapted to set a dose of medicament to be injected from an injection device,
• a plurality of light generators each for generating a beam of light towards the rotatably mounted member,
• structure for guiding light beams from the plurality of light generators to the rotatably mounted member and structure for guiding light beams from the rotatably mounted member to a plurality of light sensitive elements or areas,
• a control circuit coupled to the plurality of light sensitive elements or areas to determine the position of the rotatably mounted member relative to the plurality of light sensitive elements or areas, and
• whereby the arrangement is structured to determine the position of a dose setting member relative to the plurality of light sensitive elements or areas.