The computer controlled telescope can accept autoguider input via two methods:

1. LX200 protocol: scope.exe knows about the guiding commands available in the LX200 communications protocol.  Simply hook up the serial port from the guiding computer via a null modem cable to the serial port being used as the LX200 communications port on the computer running scope.exe.  Martin Niemi's superb quickcam autoguider will do this very inexpensively.

2. Relay box: The autoguider needs to supply a relay for each direction, or, a +5 VDC TTL signal for each direction, or, a serial connection sending LX200 protocol commands.

If using a relay box, wire the interface circuit such that when a relay closes,  a +5VDC TTL signal is supplied as follows:
If using a control signal, tie the control signals so that the control signal going to logical high raises the input voltage to a +5VDC level as follows:

(this scheme mirrors the four direction buttons on the hand paddle)
  up or north: to pin 13 of the parallel port, down or south: to pin 12 of the parallel port, left or counterclockwise: to pin 10 of the parallel port, right or clockwise: to pins 13 and 12 of the parallel port.

Here is how Juan Herrero hooked up his SBIG ST4 autoguider to the hand paddle:

Purchase a 2 female to 1 male phone wire adapter. Plug the male side to the control board.. Plug the hand paddle to one of the females. The other female will be for the ST-4. Purchase a phone wire with a male plug at one end to plug into the 2 to 1
adapter at the control board. At the other end of the wire. Install the correct computer plug to connect to the ST-4. You need to install 2 small signal diodes in two of the wires. Install the 2 diodes inside the computer plug.
The wire assignment is as follows:

ST-4 action   HAND PADDLE    PARALLEL PORT   ST-4 pins
+5v       white              n/a    ----------------------- 11, 5, 14, 8
-Az       yellow             10     ----------------------- 10
+Az       green              12     ---------|<|----------- 4 *
+Az       black              13     ---------|<|----------- 4 *
-Alt       green              12     ----------------------- 7
+Alt      black              13     ----------------------- 13

* -----|<|----- This symbol represents a diode and they are a must for thing to work.

Both the hand paddle and the ST-4 can be operated at the same time although conflicting simultaneous signals can be sent to the PC in this fashion, resulting in unpredictable actions.

To operate: