I have a simple spitter set up using a dropper into a water stream, fed by a hopper from above.

The arrangement is as follows below the hopper

O

SOP

DCB

O = Observer, S=empty space, P=sticky piston, D=dropper, C=comparitor, B=stone block

The observers are facing each other so that when the comparitor detects items in the dropper, it sends a signal into the solid block which powers the piston, pushing the observer in front of the other observer, creating a clock.  Once the dropper is empty the piston pulls the observer back, and the hopper above the dropper locks (for no apparent reason as it is not powered).  There is no other redstone in the area.  Anything placed above the hopper sits and despawns.