DOSAGE MEASUREMENT MODULE ON INJECTION PEN

The present disclosure relates to a medication delivery device. In one arrangement, the device comprises a device body. A dose setting member is attached to said device body and rotatable relative to said device body about an axis of rotation during dose delivery. A sensed element is rotationally fixed with said dose setting member, said sensed element including alternating first and second surface features radially-spaced about the axis of rotation of said dose setting member. Said sensed element and said dose setting member rotate relative to said device body during dose delivery in relation to an amount of dose delivered. A rotation sensor includes a light source emitting sensing light in an axial direction during dose delivery, and a light sensor positioned to receive the sensing light during dose delivery. The light source and the light sensor are axially disposed relative to one another, wherein in response to rotation of said sensed element during dose delivery the alternating first and second surface features are positioned directly between the light source and the light sensor in a path of the sensing light to vary light intensities detected by the light sensor. An electronics assembly responsive to the rotation sensor determines the amount of rotation of the sensed element based on detection of the varying light intensities.