NexStar Resource Site

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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



Not connected




Move RA Positive


Move Dec Positive


Move Dec Negative


Move RA Negative


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Michael Swanson
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