Ok before this thread is laid to rest, I thought I would pitch out one more option to people who may not be electrically inclined enough to build a relay or a PLC circuit.
Here is a drawing using a DC motor, two limit switches to stop the motor, two bypass diodes, and a Double Pole, Double Throw switch (DPDT)
At the top of this drawing, I show the back side of a DPDT switch. Notice it has 6 terminals.
To the right is the electrical schematic, which is just a lot easier to draw than the "real to life" drawing on the left.
The DPDT switch is really two switches in one (Double pole). It can be switched to connect a pole to the top terminal, or the bottom terminal. (Double throw).
Each pole switches at the same time.
Switch handle up, left center terminal connects to left top, right center to right top.
Switch handle down, left center to left bottom, right center to right bottom.
In the next diagram, I show the DPDT switch "turned on it's side".
(Left of the diagram is top of the switch)
I wire the top left terminal to the bottom right terminal. I wire the top right to the bottom left. (This forms an "X" on the switch's terminals.)
I then wire power supply negative to top right terminal, power supply positive to top left terminal.
The motor wires to the center terminals.
When you flip the switch, it reverses the current flow through the motor.
Switch up, motor turns clockwise (CW), switch down, motor turns counter clockwise (CCW).
Pretty simple huh?
Now we need limit switches to stop the motor from turning when the monitor reaches the correct position.
I have added two limit switches, both are normally closed.
The CWLS switch opens when the monitor reaches the end of clockwise rotation.
The CCWLS switch opens when the monitor reaches the end of the counter clock wise rotation.
You will also notice two diodes.
These diodes provide a reverse path for the current to flow, when the limit switches are open.
Follow the center diagram. I have drawn a red line to denote negative current flow to the motor, and a blue line to denote positive current flow from the motor.
When the switch is turned to the up or clockwise position, Current flows from the negative power supply, through the right side of the switch, through the CWLS switch, through the motor. Now the line turns blue and the current flows through diode D2 (Because the CCWLS is open until the motor starts to turn), through the left side of the switch, back to power supply positive.
The motor turns until CWLS opens, breaking the circuit and stopping the motor.
Now we flip the switch to "down" to turn the motor CCW.
The current now flows from negative through the left side of the switch, down through CCWLS, up through motor, turning it CCW.
The current flows out of the motor through D1 (remember CWLS is open at start, so D1 provides and alternate path), around through the right side of the switch, back to power supply positive.
Motor turns CCW until CCWLS opens.
This is just about as simple and cheap way of reversing a motor that I can think of.
It does have its drawbacks though. It is not nor can it be made automatic. (My goal).
Plus you will have to mount a switch somewhere. It will most likely be a "bat handle" switch and wont match your others, although you could hide it.
Also, the switch, the limit switches, and the diodes must all be rated to handle the current of the motor. Also, motor braking cannot be applied, so mechanical stops become a must have thing. (Although I would use them in any design anyway.)
Ok, I'm getting off my soap box now.