PC, Mac, Tablet and Smartphone Control of NexStar Telescopes
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.
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 communicate with the scope via the port on the bottom of the hand control. Current hand controls (manufactured since April 2016) have a USB port while older hand controls have an RS-232 port (looks like a phone jack). For more information about the various ports and connectors on your scope, visit the Odds and Ends section of this web site.
Wired Connections for USB Hand
At this time, I know of no method of making a wired connection between a table/smartphone and the USB hand control.
Wired Connections for RS-232 Hand Controls
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. 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. Once you connect your USB adapter, a serial port, designated by a number, will be present on your computer. Configure your astronomy software to connect to this port.
Wired connections to a tablet or smartphone are pretty much limited to Simulation Curriculum's SkyWire and their SkySafari application. This adapter is only compatible with specific iPhones, iPods and iPads. See their website for more details.
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 to the RS-232 hand control.
Wireless control takes two basic flavors - Bluetooth and WiFi.
There is one Bluetooth adapter designed specifically for telescope control: 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 first is Celestron's WiFi solution. The NexStar Evolution and the Astro Fi scopes have built-in WiFi. Celestron sells their SkyPortal WiFi Module (part # 93973) which is compatible with many of their other 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 - part number 93973). In fact, I generally use the splitter as an extender on most mounts to allow the WiFi module to hang loose rather than providing a hook for things to get caught on. The Evolution, Astro Fi and SkyPortal WiFi Module are only compatible with the SkySafari and SkyPortal apps on Android and iOS. This is a unique solution as SkyPortal/SkySafari and your smartphone or tablet completely take the place of the physical hand control - you actually perform the alignment and all further operations inside the app itself. The only thing similar is NexRemote (see the link in the top, right of the page) which takes the place of the physical hand control and runs on a Windows PC.
Second, Simulation Curriculum offers SkyFi 3. SkyFi 3 connects to either the RS-232 port on the bottom of the serial hand controls or the USB port on the bottom of the newer hand controls - 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.
Next, Software Bisque supports connections from their software, TheSkyX, with a device named "WiSnap WiFi to RS232 Adapter". Documentation on the use of TheSky is here. The device doesn't seem to be available at their website but can be purchase from the manufacturer - Serial IO. Most other Windows software should be able to connect via the WiSnap using AstroGeeks' (www.AstroGeeks.com) COM2TCP software though configuring the adapter and COM2TCP could be a significant hurdle.
Finally, ScopeCom and ScopeCom-II allow WiFi connections from Android, iOS, Mac and Windows devices to any of the serial port hand controls (not the newer USB hand controls). On Android and iOS, connections may be limited to SkySafari, though other software may work. On Mac and Windows computers, any software that can communicate via a wired serial connection should work fine.
Putting It All Together
With SkySafari using the WiFi connection method, SkyPortal, or NexRemote, you will first perform an alignment in the software/app itself. For all other software, you must first perform a regular alignment with the physical hand control before attempting to control the scope with the external software/app.
Start your astronomy software and the computer should be ready to communicate with your telescope. Some programs have a menu item or toolbar button to establish communication while other programs are ready to talk immediately after starting; refer to the documentation for your program if this is not readily apparent. The software/app may require some configuration settings such as setting the type of scope and the communication port the scope is connected to. A good test for communication is to direct your program to retrieve the telescope's coordinates, or, if it is planetarium software, the crosshairs on the screen should follow the telescope as you slew around. The next test would be to use the program to direct the scope to GoTo an object. If the coordinates match within a few arcminutes, then all is working properly. If the telescope doesn't move at all, check the LCD panel on the hand control for a slew limit warning - the object you requested might be outside your established Slew Limits.
If things don't seem to be working as expected, refer to the 'troubleshooting' articles at the top of the page.