SkyFi USB and Serial Interfaces

Connecting SkyFi to a Meade Autostar controller.

Please Note: SkyFi is now owned and supported by Simulation Curriculum Corporation. This page contains legacy information for owners of older versions of the app. For the latest information on SkySafari for Mac OS X, go to

This page contains instructions for connecting your telescope's serial (RS-232) or USB port to SkyFi's serial or USB port.

With USB telescopes, use a standard USB cable to connect SkyFi's USB “A” port to the telescope's USB “B” port. On Meade LS telescopes, the USB “B” port is on the mount base. With iOptron telescopes, the USB “B” port is on the GOTONova hand controller.

With serial telescopes, you'll need a serial cable that connects your telescope's serial port to a standard PC serial port. Different telescopes require different serial cables, so contact your telescope's manufacturer to obtain the correct serial cable for your telescope.

Once you've obtained the correct serial cable for your telescope:

  1. Connect your telescope serial cable to the RS-232 port on your telescope. On most telescopes, the RS-232 port is a 4- or 6-pin modular ("telephone") jack. On Meade LX-200 and LX-400 telescopes, the RS-232 port is located on the mount base. On almost all others (e.g. Meade telescopes with #497 AutoStar controllers, Celestron telescopes with NexStar controllers, Orion and SkyWatcher telescopes with Synta controllers), the RS-232 port is located on the bottom of the hand controller.

  2. Connect the other end of your telescope's serial cable to the DB9 male connector on SkyFi's serial adapter. Insert the other end of the serial adapter into SkyFi's RJ-11 serial connector. Make sure the connector clicks into piace securely.

IMPORTANT: Do not connect SkyFi to the AUX port, handbox port, autoguider port, or any other port on your telescope (or its hand controller) than its RS-232 serial port. Doing so may damage SkyFi and/or your telescope hardware. Make sure you know where the RS-232 serial port on your telescope is located, and only connect SkyFi to that port.

For Meade LX-200 and LX-400 telescopes, the RS-232 port is located on the mount base. For Meade telescopes that use the #497 Autostar controller, like the ETX and LX-90, the serial port is located on the bottom of the Autostar. For all Celestron telescopes using the NexStar hand controller, the serial port is located on the bottom of the NexStar hand controller. For Orion and SkyWatcher telescopes, the serial port is also located on the bottom of the Synta hand controller.

You don't need to use the mini null-modem adapter supplied with SkyFi when connecting it to a telescope. This null-modem adapter is only needed when connecting SkyFi to a PC serial port for firmware updates. Click here for details.

You can attach SkyFi to your telescope's mount or tripod with the supplied strip of Velcro. Make sure SkyFi's serial adapter is not kinked, that there is a decent amount of slack in your telescope serial cable, and that all connectors are fastened securely.

Building Custom Serial Cables

Carbon 12 AstroSystems builds high quality serial cables which can connect directly from SkyFi's serial port to the serial ports on a wide variety of different telescopes. Click here for details.

Alternately, you can build a custom serial cable to connect your telescope to SkyFi, without using SkyFi's RJ-11-to-DB9M adapter.

Like SkyFi, most telescope serial ports also use 4- or 6-wire modular jacks. Unfortunately, telescope manufacturers have not standardized on a common serial port pinout. In other words, pin 1 on the serial jack for a Meade LX-200 may carry a different serial signal than pin 1 on the serial jack for a Celestron NexStar GPS.

If you can obtain the pinout diagram for your telescope's serial port, you can build a simple "telephone" cable to connect SkyFi's serial port directly to your telescope's. The following diagram shows the meaning of the pins on SkyFi's serial adapter cable:

Pinout diagram for SkyFi's RJ-11 to DB9-M serial adapter.

This diagram, combined with your telescope's serial pinout diagram, should allow you to construct a simple telephone-like cable for connecting SkyFi's serial port directly to your telescope's serial port. The following table lists the pinouts for SkyFi's serial adapter, and for several common telescope models. Note that some telescope serial ports use a 6-pin RJ-11 connector similar to SkyFi's; while others use the smaller 4-pin modular "handset" connector. Check your telescope manual for details, and expect some trial and error.

Manufacturer:Southern StarsGenericSouthern StarsCelestronCelestron,
Others (*)
Model:SkyFiPhone CordSkyFiNexStar, CGE,
Others (*)
IntelliscopeSynScanETX, LX-90,
Classic, GPS
ServoCATArgo NavisGeminiSkyTracker

X = do not connect this pin/wire!

(*) The Celestron AstroMaster shares the same pinout as a number of other encoder control boxes based on the Tangent Instruments BBox. In addition to the BBox, such encoder-based systems include the JMI NGC-MAX, Lumicon SkyVector, and Orion SkyWizard.

Pins are numbered 1 to 6 from left to right when facing the connector with the pins down and plastic clip up, as pictured above. Note that the outermost pins (1 and 6) are not used on any 6-pin RJ-11 connector!

For ServoCAT and Argo Navis users, this document contains cable pinout diagrams and setup instructions. For Starmaster Sky Tracker systems, this document contains the equivalent instructions.

Please note that Southern Stars does not provide support for building custom serial cables.

SkyFi's Serial Hardware

SkyFi's serial port supports baud rates from 300 to 230400 bits per second, and includes the transmit data (TD), recieve data (RD), and ground (GND) signals. SkyFi's serial port does not support hardware flow control. However, very few serial devices actually require hardware flow control, so this should not be a problem for most applications.

The pins on the DB9 male end of SkyFi's adapter correspond to exactly the same pins on a real PC serial port. In other words, the DB9 male connector on SkyFi's serial adapter works exactly the same way as a PC serial port.

To connect SkyFi's serial port to a real PC serial port, insert a null-modem adapter between the DB9 connector on SkyFi's adapter cable, and the DB9 connector on the PC. A female-female mini null-modem adapter is included with SkyFi for exactly this purpose. You'll need to use this adapter when connecting SkyFi to a PC serial port for firmware updates.

Configuring SkyFi's Serial Settings

SkyFi serial settings configuration.
Click to enlarge.

You can use a web browser to configure SkyFi's serial port settings. To do this, first join SkyFi's wireless network, then browse to, or to whatever IP address you have assigned to SkyFi.

The baud rate, parity, number of data bits, and number of stop bits, can all be selected from the dropdown menus at the bottom of SkyFi's configuration web page. You can also select the TCP port on which SkyFi will transmit data from its serial port to the wireless TCP/IP network, and vice-versa. By default, that TCP port is 4030, but you can use any other port from 1024 to 65535. Only one network device can be connected to this TCP port at a time.

When you are finished, click the "Save Changes" button. Note that this will interrupt any serial communication already in progress.

Programmers writing custom applications can control SkyFi's serial settings using standard HTTP requests with simple CGI parameters. The HTTP requests should be sent to SkyFi's IP address on port 80. The CGI command is /setserial, and the CGI parameters are as follows:

Serial Setting:Baud Rate
(bits per sec)
Parity Setting
(none, even, or odd)
Data BitsStop BitsTCP Port
CGI Parameter:baudparitydatastoptcp_port
Possible Values:300



The HTTP response code will be 204 (no content) if the request succeeded, or 500 (server error) if the request failed. If the parameters are incorrect, SkyFi will not change the serial settings. Here is an example:

This will set SkyFi's serial port to use 19200 baud, even parity, 5 data bits, and 2 stop bits. Serial data will be relayed to and from the wireless network on TCP port 5678.