Lever 1 turns about fixed axis A and has spring 3 which is bent in the shape of a slotted link sliding along pin d of disk 2. Disk 2 turns about fixed axis B and has pins b and c. In the position shown, one of pins c is against stop a and one of pins b against end e of lever 1. When lever 1 is turned counterclockwise, spring 3 presses against pin d and turns disk 2 since end e of lever 1 turns away and releases pin b. Disk 2 turns through an angle determined by the distance between pins c. After this, lever 1 can be turned back to its initial, position.
$2112$EL,4L$