NexStar Resource Site
Site Map

line.gif (861 bytes)
Home | NexStar User's Guide | NexStar Observer List | Downloads | PC/Mac/Tablet/Smartphone Control
Odds and Ends | Firmware Versions | Equip Reviews | Alignment Guides  | Manuals | Links
line.gif (861 bytes)

PC, Mac, Tablet and Smartphone Control of NexStar Telescopes

It is first important to understand that as the NexStar system evolved, three different control protocols were introduced. 

  1. The first NexStars on the market were the original NexStar 5/8 sold from 1999 to mid 2002.  These scopes had a silver optical tube and no connector ports on the top of the mount.  They also have a control protocol unique to them, so if a software does not state specifically that it is compatible with this mount, it most likely will not communicate. 
  2. Next on the market were the NexStar GTs in 2000.  The original hand control can be identified by a lack of the alignment option named Two Star Align.  The original hand control had a slight change to the control protocol from the NexStar 5/8 and thus introduced the second unique protocol.  There are very few software package compatible with this hand control.
  3. With the advent of the NexStar GPS series in 2001, Celestron introduced what would become their final (up to this time) control protocol.  The NexStar GTs received a hand control update in 2001, identifiable by the addition of the Two Star Align option, which used this same control protocol.  The original NexStar 5/8 were never upgraded but were replaced by the NexStar 5i/8i which also used this new control protocol.  All Celestron computerized mounts introduced since then also use this control protocol.

Additional Info

Software/Apps Compatible with NexStar, CGE, CGE Pro, CGEM and AS-GT Scopes
Problems with PC to Scope Communications
Problems with PDA to Scope Communications
Hand Control RS-232 Port Cable
PC Port Cable
Diagram by Larry McNish Depicting NexStar Cable/Port Connections
NexRemote -  Software to Replace the Hand Control with a PC
Programming for NexStar Controlled Telescopes - Documentation and Examples

So, when configuring your external software/app, if it requires the selection of telescope type, look first for your specific model (NexStar SLT, CPC, etc.).  If your model is not available, try NexStar GPS or CPC.  If Celestron is the only option, select that.  Feel free to experiment, but be ready to press any of the arrow buttons on the hand control if the mount seems to be slewing out of control and it looks like the optical tube might strike the mount.

PC and Mac software generally communicates with the scope via the RS-232 port on the bottom of the hand control.  This is what is known as a 'serial' port connection.  For more information about the various ports and connectors on your scope, visit the Odds and Ends section of this web site.  The correct cable to connect to this port is described in the link "Hand Control RS-232 Port Cable" above.

If your PC/Mac does not have a serial port (serial ports are very rare with today's laptop/notebook computers) you will also need some sort of adapter.  If your laptop has an ExpressCard or PC Card slot (also rare today), your best bet is an RS-232 port ExpressCard/PC Card ($40 to $100).  RS-232 port ExpressCard/PC Card adapters can be hard to find in a local store.  Click here for Google results for RS-232 PC Cards.  Click here for Google results for RS-232 ExpressCards.  The next option, and the one you will most likely use, is a USB to serial adapter ($30 to $40).  Most computer stores stock USB to serial adapters but not all work well with Celestron's scopes.  I recommend you purchase Celestron's own USB to serial adapter (Celestron part number 18775) or an adapter that specifies it uses either a "Prolific" or "FTDI" chipset.

Wired connection to a tablet or smartphone is pretty much limited to Simulation Curriculum SkyWire and their SkySafari application.  This adapter is only compatible with specific iPhones, iPods and iPads.  See their website for more details.

Wireless control takes two basic flavors - Bluetooth and WiFi.  Bluetooth RS-232 serial adapters connected to the RS-232 port on the bottom of the hand control take the place of the standard control cable and can work with a wide variety of software/apps.  There are several generic adapters on the market for $40-$60 dollars though they are not designed specifically for this purpose and some may simply not work.  But, since Bluetooth is supported by Windows, Mac and Android devices, this is a very attractive option.  Essentially, the Bluetooth adapter presents itself to your computer/tablet/smartphone as a serial port.  Thus, any astronomy software or app that can communicate with a serial port (those designed for the standard cable connection) can potentially use this configuration.  I am unaware of any iOS (iPhone/iPad) app that communicates with serial ports, but the WiFi option is available for iOS.  If you decide you would like to experiment with Bluetooth adapters, you will want your Hand Control RS-232 Port Cable to be fairly short.  Also be sure the adapter has a power source that works well for this purpose, such as an internal battery.

There is one Bluetooth adapter designed for telescope control currently on the market: Simulation Curriculum's SkyBT.  SkyBT is an adapter specifically designed for Android which will also work with their software products for the Mac.  This option is tested with their SkySafari software but may work with other software. 

The second method of wireless control uses a WiFi connection similar to your home router or the Internet service at your local coffee shop.  WiFi adapters for your scope are only compatible with a limited selection of software/apps.  There are a few possibilities in this arena.  First, the NexStar Evolution and the Astro Fi scopes have built-in WiFi.  Second, Celestron sells their SkyPortal WiFi Module (part # 93973) which is compatible with many of their scopes - check their website to see if yours is supported.  The SkyPortal WiFi Module plugs into an Aux jack on the scope and may require an "Aux splitter" (also available from Celestron).   The Evolution, Astro Fi and SkyPortal WiFi Module are only compatible with the SkySafari and SkyPortal apps on Android and iOS.    Third, Simulation Curriculum's offers SkyFi 3.  SkyFi 3 connects to the RS-232 port on the bottom of the hand control - again, check their website for telescope compatibility.  SkyFi 3 is compatible with SkySafari and SkyPortal on Android/iOS and SkySafari and Starry Night on Mac/Windows.  Fourth, Software Bisque supports connections from their software, TheSkyX, with a device named "WiSnap WiFi to RS232 Adapter".  Theoretically, most software should be able to connect via the WiSnap using AstroGeeks' (www.AstroGeeks.com) COM2TCP software in the middle though configuring the WiFi to serial adapter could be a significant hurdle.

Before smartphones, many people owned a PDA ('personal digital assistant', Palm Pilot, Pocket PC).  If you have one stuffed in a drawer somewhere and want to try it out, PDAs require a serial "sync" cable or a serial port CF card which is used to connect to the Hand Control RS-232 Port Cable.  When using a CF card, the standard hand control RS-232 port cable is used.  When using a serial "sync" cable, you will need a null modem and gender changer to use the hand control RS-232 port cable or a custom cable.  Details of these cables are explained in the link "Hand Control RS-232 Port Cable" above.

Be sure to check out Larry McNish's diagram linked above for various cable connections.

Most of the information you find here is the result of my work on NexStar Observer List, a PC control program for all models of NexStar scopes.  You can learn more and download your free copy here.


line.gif (861 bytes)
Copyright 2000-2017
Michael Swanson
 
  Contact the webmaster:
swanson.michael@usa.net