Timer for controlling a water solenoid to top off an aquarium when the float switch senses low level . The 0 leg is attached to a transistor that switches a relay to tun on the solenoid. There is a fail safe built in to the code that only allows the water to run for 7 seconds. If the float switch has not switched off by the end of 7 seconds the 0 leg output is turned off and "E" (for Error) is displayed. There is a pause after the fill process to allow the float switch to stabilize.