NexStar Resource Site

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Hand Control RS-232 Port Cable

To allow an external computer to communicate with your scope, one option is to connect to the RS-232 serial port on the bottom of the NexStar/StarSense hand control.  The same cable works for all NexStar/StarSense models and you can order one from most Celestron dealers (Celestron part number 93920).   (Note that hand controls manufactured after April 2016 have a USB port and require a USB cable - see this page for more information.)

This cable is also used to update the firmware in user-upgradeable versions of the hand control and starting with hand control version 4.13, can be used to update the firmware of the motor control in the mount.

If you decide to build one, here's what you need to know.  Buy a telephone handset cable, the coiled type that goes from the handset to the telephone - a standard phone cable does not have the correct connector.  Be sure it has four colored wires visible at both ends; some cables only have two.  Remove one of the RJ plugs and attach a DB-9 connector matching the drawings below:

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NexStar End of Control Cable
(connects to bottom of NexStar hand control))


DB-9 End of Control Cable
(connects to serial port on the computer)

Note that the top drawing represents the end of the cable that connects to the NexStar hand control (this is an RJ-22) and the bottom drawing represents the end that connects to the serial port on the PC (this is a female DB-9) or on a PDA's serial CF card.  The DB-9 connector will be male rather than female and pins 2 and 3 will be reversed at the DB-9 connector if you are connecting to the "sync" cable for a PDA.  It is best to make the DB-9 end by crimping an RJ-11 connector (a standard phone connector) on one end of the cable and using a DB-9 to RJ-11/12 adapter (shown below), which can be found at (search for "db9 rj11").  If all of this seems complicated, better buy a pre-made cable ;-)

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Michael Swanson
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