Telescope Control in Stellarium Mobile PLUS

Telescope Control

Since version 1.1.0 Stellarium Mobile PLUS allows to control a GOTO telescope directly from the phone, by using NexStar/SynScan or LX200 serial protocols. Most (but not all) of the current GOTO telescope are compatible with one of these protocols.

In order to have your phone talk to the telescope controller, you first need to connect it to your mount or hand controller. The currently supported modes are:

  • Network connection (serial over a TCP socket). This covers Wifi enabled telescopes, LAN connection, or SynScan mounts when using the SynScan app (see below).
  • Bluetooth connection. Currently bluetooth 2.0, using SPP profile. This one works only on Android, because iOS doesn’t allow apps to use Bluetooth SPP.

In many case, the telescope mount hand controller exposes a Serial RS232 port which needs to be plugged into a Serial-to-WIFI or Serial-to-Bluetooth converter so that the phone can access to it. Tested controllers for many type of mounts can be for example found on Astro Gadget .

On Android, for many phones models, it is also possible to connect to the mount using a USB Host adapter cable, and a third party app creating a local TCP socket redirecting ot the USB port. For example the app “BT/USB/TCP Bridge Pro” (3.49€ on Play Store) was reported to work.

Once you define the type of link between the scope and phone, this is basically it! Stellarium Mobile Plus will try hard to automatically recognize the protocol, the type of mount, and mount status and all other available information about the hardware whenever possible.

Using the SynScan app as a bridge between Stellarium Mobile PLUS and the telescope

SynScan-based Wifi mounts such as the SkyWatcher Az-GTi can be controller without hand controller. For this, you need to install the official SynScan android or SynScan iOS apps and use it to connect to the telescope, configure and align it. The SynScan app opens a TCP socket on the phone on port 11882 emulating a regular SynScan hand controller protocol. Once the telescope is setup, start Stellarium Mobile PLUS (keeping SynScan app running in the background) and connect to it using a “Network” connection type, on host, port 11882.

Warning 1: On iOS, it is not possible to have the SynScan app running in the background. The only way to drive your telescope on iOS using the SynScan app is currently to have it running on another device (either iOS or android).

Warning 2: on some android phones, the OS decides to kill SynScan app when it’s running in the background, presumably because it’s using too much resources or battery. This causes the connection to be lost between Stellarium and the telescope. To solve this issue, it is necessary to change the android settings for SynScan app to avoid it being killed too quickly. These settings are OS dependent, but usually it helps to disable the battery saving, set Synscan app to “do not optimise”, or “ignore optimizations”. This is how to change these settings on Huawei .

We have been receiving reports about an issue with Synscan and after contacting the Sky Watcher guys, they acknowledged that there is an issue in the recent SynScan apps version. Here is what they said:

  • The current SynScan Pro app for Android released on Google Play can not work in the background to provide TCP/UDP server communication. We are working on this issue. A temporary solution is to run the SynScan Pro app in a smaller FreeForm window, a floating window, or a splitting window; and run the Stellarium in a larger window; if the user’s Android phone supports these features, as shown in the attached picture.
  • Users can download and install SynScan Pro for Android version 1.19.16 from our website.

Sky-Watcher website

Using a linux computer as a bridge between Stellarium Mobile PLUS and the telescope

It is also possible to use a computer sitting next to the telescope as a bridge. In this case you need to plug the Serial RS232 port of the telescope hand controller to your PC using a (cheap!) Serial to USB cable. You can then tell your PC to forward the telescope data to a local TCP socket on which Stellarium Mobile can connect.

On linux this can be done with the socat command line tool using a single command:

socat TCP-LISTEN:10000,fork,reuseaddr FILE:/dev/ttyUSB0,b9600,raw,echo=0

This command tells your PC to create a new TCP socket on port 10000 on which it should forward the content of /dev/ttyUSB0. The device /dev/ttyUSB0 is the serial port data coming from your telescope. Depending on your configuration you might need to change the name of the device to /dev/ttyUSB1 etc..

In order for this command to work you must also make sure that your current user is allowed to access tty devices. For example on ubuntu it needs to be part of the tty and dialout groups.

To see the groups you are in simply type:


to add yourself to the groups mentioned above type:

sudo usermod -a -G tty [yourname]
sudo usermod -a -G dialout [yourname]

and logout/login to apply the changes.

You can then connect Stellarium Mobile to your PC by connecting your phone to the same WIFI network, and then inside setup Stellarium Mobile so that it connects to it. You need to select a ‘Network’ link type and use the IP adress of your PC (usually 192.168.x.x) as a host, on port 10000.

Controllers compatibility list

In general, all controllers compatible with some forms of the LX200 protocol, or with NexStar protocol should be auto-detected, even if not specified in the table below.

The following controllers are known to work fine with Stellarium Mobile PLUS:

Brand Controller Status Notes
Meade LX200 Classic Tested Require Serial-to-Wifi/Bluetooth/USB Host converter
Meade Autostar #497, Autostar #497EP, Audiostar Tested Require Serial-to-Wifi/Bluetooth/USB Host converter
Meade Autostar II Tested Require Serial-to-Wifi/Bluetooth/USB Host converter
Meade Computer Drive System #1697 Should Work Require Serial-to-Wifi/Bluetooth/USB Host converter
10micron All Should Work Require Serial-to-Wifi/Bluetooth/USB Host converter
Starmate All Should Work Require Serial-to-Wifi/Bluetooth/USB Host converter
Celestron Nexstar Hand Controllers (Nexstar GPS etc..) Tested Require Serial-to-Wifi/Bluetooth/USB Host converter
On-Step On-Step controller Tested Work both on WiFi (port 9998) and Bluetooth
TeenAstro TeenAstro controller Tested Work on WiFi (port 9999) with TeenAstro v1.5.1+
aGotino     aGotino Arduino-based controller             Tested     Work both on WiFi and Bluetooth        
SkyWatcher SynScan Hand Controllers Tested Require Serial-to-Wifi/Bluetooth/USB Host converter
SkyWatcher SynScan Wifi Mounts (Az-GTi etc..) Tested Using the SynScan App as a bridge (see above)
AstroDevices Nexus DSC (likely work on other Nexus) Tested Require the last firmware and Stellarium+ >=1.7.3
GOTOTELESCOPE INC. MX-HD Tested Work both on WiFi and Bluetooth

The following controllers are currently not supported:

Brand Controller Status Notes
iOptron SmartEq etc.. Not working Currently unimplemented serial protocol
Explore Scientific PMC-Eight Not working Currently unimplemented serial protocol
Omegon Push+ Go Not working Currently unimplemented serial protocol

Other resources

One of our users wrote a guide on How to control your USB enabled scope with Stellarium Mobile PLUS