Often designers build a farm in Minecraft or other designs, which used pistons, dispensers, etc. because of the nature of such structures above mechanisms have to work constantly – gripping mobs, shoot them with snowballs or arrows. Constantly give the signal for the operation of such parts of the mechanism helps to use short circuit. This open-loop system that disables itself with an amplitude of about 2 times per second.
To do this, you'll need three of any unit (for example, brick), four red lights, a switch and a dozen particles of red dust.
Set on a flat surface with two bricks, leaving an empty space between them. Depart from this place another block and put the last brick perpendicular to the previous. The result should be a triangle (if you imagine this design on the bench, the bricks will be placed in the lower cells of the first and last columns, as well as in the upper cell of the middle column). On top of the bricks you need to put on a bit of red stone. Between two bricks at the base must also put the red stone particle, and draw a line to a single unit, combining all in a single chain. On a single block you need to install a switch, to connect the system with the mechanism, you need to draw a line of red stone from the middle of the base to the piston or the distributor.