English: This is an illustration of a machine to demonstrate working principles of limit switches. Electric motor (1) turns drive pulley (2), which pulls string (3). The string(3) rides on idler pulleys (4), and attach to actuating block (5) by being tied to eye screws (6) Tension compenasator spring (7) takes up slack in string(3), though spring (6)woulc desirably be placed in the center of the drive pulley so as to not interfere with the idler pulleys(4). At extremes of motion, block (5) hits tip of household light switches(8). As shown, house switches (8) have been modified by drilling holes(9) transversely through the tips of their operating levers, and elastic devices (10) such as springs or rubber bands attached thereto, the opposite ends of which are secured to nails or screws (12) driven into switch mnounting blocks (11). The elastic or spring return elements (10) convert ordinary household switches (8) into momentary switches of either type desired (N.O. or N.C.) Switches (8) are wired into motor drive circuitry in such a way that they prevent further motion in the direction which activated the switches, but allow the motor to run in the oppposite direction.