Abstract: A dose counting system of an injection device or of a module configured to be used with or applied to an injection device is described. The dose counting system includes a sensor arrangement including a first sensor configured to output a first signal and a second sensor configured to output a second signal; and a processor configured to: detect a peak in the first signal when the first signal has increased by at least a predefined up threshold and the first signal exceeds the value of the second signal by more than a predetermined crossover threshold; determine that a unit of medicament has been administered when the first signal drops from the peak by more than a predefined down threshold and the preceding peak occurred in the second signal; and determine a medicament dosage administered by the injection device by counting the administered units of medicament.

Abstract: An optical guiding device configured for application with a drug delivery device is described. The drug delivery device has (i) a movable dosage programming component including a rotary encoder system and (ii) a sensor arrangement including at least one optical sensor. The at least one optical sensor is configured to detect movement of the movable dosage programming component relative to the sensor arrangement during dosing of a drug by emitting radiation and detecting at least one reflections the emitted radiation from the rotary encoder system. The optical guiding device is configured for guiding the radiation and the at least one reflection of the emitted radiation and includes at least one light pipe having the shape of a frustum with a sensor-side surface and a encoder-side surface.