NexStar Resource Site

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Ports and Connectors on CGEM Scopes

Click here for a diagram by Larry McNish depicting NexStar cable/port connections.

  • RS-232 Port - located on the bottom of the hand control.  The primary usage of this port is for controlling your scope with the wide variety of astronomy software available for PCs, Macs and PDAs.  A secondary usage is for updating the motor control firmware in the mount - details are found here.  The connector is a 4 conductor RJ-22 - the slim connector used for most telephone handset cords.  The signaling is standard RS-232 levels.  Click here for details on the cable used to connect this port to a PC.
  • HAND CONTROL Port - located on the control panel on the right ascension motor housing.  This is the port for connecting the hand control to the mount.  The hand control may also be connected to the AUX port.  The connector is a 6 conductor RJ-12.  The signaling is TTL and so a serial port on a PC should not be connected to this port.
  • AUX Port- located on the control panel on the right ascension motor housing.  This port is designated for "smart accessories", for example, the optional CN-16 GPS module - Celestron part number 93963.  Also, as noted above, the hand control can be connected here as well.  The connector is a 6 conductor RJ-12.  The signaling is TTL and so a serial port on a PC should not be connected to this port.
  • AUTO GUIDE Port - located on the control panel on the right ascension motor housing.  This port is designed for connecting a standard autoguider - generally based on a CCD camera.  The connector for this port is an RJ-12 and the pin designations are found here.  Also, you can build or buy a manual hand control that allows manual guiding or fine movement control and connect it to this port - details are found here.
  • POWER CORD Connector - located on the control panel on the right ascension motor housing.  This is the connector for the power source driving the scope - details on this connector are found here.

Also, it should be noted that Celestron offers an Auxiliary Port Accessory Kit (part number 93965) that can be connected to the HAND CONTROL port and then provides the following ports:

  • AUX 1 and AUX 2 Ports.  Two AUX ports with the same function and description noted for the AUX port above.  Most likely you will have no reason to purchase the aux port kit for these additional ports.
  • PC Port.  This port can be used with two software packages from Celestron.  The first is for upgrading the motor control firmware, though with a functioning hand control, motor control firmware can be updated via the RS-232 port on the bottom of the hand control as well.   The second is for a PC-based virtual hand control called NexRemote - details are found here.  NexRemote can also be used by connecting the PC via the RS-232 port on the hand control - the PC port just has the advantage of not requiring the real hand control to even be connected.  The connector for this port is an 8 conductor RJ-45.  The signaling is standard RS-232 levels.  When using NexRemote with the PC port, you need a "programming cable", not the standard RS-232 cable used to connect to the port on the bottom of the hand control.  Click here for details on the cable used to connect this port to a PC.

And finally, Ken Hutchinson has put together a document detailing how to build an adapter that connects to the HAND CONTROL or AUX port and then provides a PC Port that works as described above.  For more on this adapter, click here.


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