OSX USB to serial connection to telescope mount - settings?

Hello there.
Please forgive me if this seems a stupid question, but I have been struggling with this for a few hours. I’m trying to connect my Skywatcher Synscan AZ GOTO telescope mount which is running the latest firmware to my MacBook Air using your serial to USB adapter configured with up-to-date drivers, and which shows up in preferences/network as USBserial controller D. I have set it to be a null modem with a baud rate of 9600. If I press “connect” I get an error message saying “A connection could not be established to the PPP server. Try reconnecting.”

Starry night software has been configured to run this particular telescope, but when I press “connect” the connection is made for a few moments before disconnecting and throwing up an error message. I don’t think the problem is with the telescope mount, the handset, or starrynight, but rather with the way in which the USB to serial adapter is configured on the MacBook air.

Does anybody have experience with this particular problem or does anybody have any idea where I may be going wrong? Many thanks in advance.


Hi Stephen,

Thank you for posting about your serial adapter. We have had several support tickets where people were able to use the starry night software successfully on a PC,

However, it looks like there may be an issue with Starry Night and PPP on OS X 10.7 and higher, depending on which Starry Night version you have. This page on the Starry Night site explains it:


Thank you,

Plugable Support

Hi David
I’ve seen that particular page, but it doesn’t apply to my situation. I’m running Starrynight Pro 7 and OSX 10.11.5, both the latest versions. I feel that the USB to serial adapter only needs a tweak to get it to “talk” to the telescope mount, but I’ve tried everything my limited knowledge can think up. I’m just looking for some pointers or ideas to try.

FWIW I’m awaiting a reply from Simulation Curriculum on this problem. Thanks again.

Hi Stephen,

Unfortunately, I don’t have a copy of the software or a telescope to test this with, so it’s hard to say conclusively, but if you run the following command in a terminal on the Mac, it will tell you if the adapter is working OK:

ls /dev | grep usbserial

if you see cu.usbserial, that is your port, and the Mac sees the cable and has installed the drivers for it. Beyond that, you may need to change port settings or set the correct port in the software, but Simulation Curriculum would probably be the best to answer these questions.