I need help designing a circuit to reverse polarity on a 12v actuator. The circuit will be started with a limit switch and from there needs to extend then retract automatically. I intend on having a timer on the circuit where I can control the time that its extended. I have looked at SGT Wookies H bridge design but don't think this is what I need. I am new at the design of circuits and not sure of what relays, diodes, 555, 556, etc. that I may need.