An activation assembly for a wellbore tool positionable in a wellbore includes a housing, a wellbore tool coupled to the housing, and a tool activator operatively coupled to the wellbore tool. The tool activator includes first and second fixedly connected circular disks, each of which includes a plurality of radially projecting teeth disposed around an outer circumferential surface of the disk. The disks are rotatably mounted about a longitudinal axis of the housing. The tool activator further includes a key member having a head portion engageable with the teeth of the first and second disks. The key member is located within the housing such that the disks rotate through a limited angular distance in response to movement of the key member.