Pin Connections in Auto Guide Port
The Auto Guide port found on the NexStar 8/9.25/11 GPS, 5i/8i/8i Special
Edition, CGE, CGE Pro, CGEM and AS-GT
telescopes is the same standard port that has been used by Celestron and
many other telescope manufacturers for years. This port is designed to
be compatible with the SBIG ST-4 standard. The ST-4 operates like four simple
switches, one for each of the four slew directions. Most autoguiders use
electronic switches and require a relay box as an interface between the
autoguider and the telescope. Some have successfully used their autoguider
without a relay box, but I would recommend the relay box. In addition to
providing the required interface, the relay box also electrically isolates
the autoguider/camera from the telescope electronics. The motors in the
scope are a potential source of electrical noise that could spoil images in
some cameras (conservative speculation on my part).
The pins in the Auto Guide port on the base of the telescope are numbered
1 through 6 going left to right as shown below. The function of each pin is
also shown. If pin 3 is electrically connected to pin 2, the telescope moves
positive in RA, pin 4 to pin 2 moves down (negative) in declination, etc.
 |
Auto
Guide
Port Pins |
Function |
|
1 |
|
|
2 |
Ground |
|
3 |
Move RA
Positive |
|
4 |
Move
Dec Positive |
|
5 |
Move
Dec Negative |
|
6 |
Move RA
Negative |
|
