After quite a while of wishing I could control my Celestron Nexstar 130SLT by computer I have finally achieved it - at surprisingly low cost. Rather than buying an expensive purpose made cable from Celestron I put together my own and it works very well.
I went to Jaycar Electronics and bought the following parts:
1. A telephone handset cable, the coiled type, that goes from the handset to the telephone - note that a standard RJ12 phone cable does not have the correct RJ11 connector (Jaycar P/No:YT-6048 $9.95 - 8 metres). Be sure it has four colored wires visible at both ends; some cables only have two.
2. An unwired DB-9 to RJ45 adapter (Jaycar Part No A-0906 $4.95), making the correct internal connections between the two sockets as per the following. Pin 2 of the female DB9 socket to Pin 3 of the RJ45 socket (connections at the top and counting from left to right), Pin 3 of the DB9 to Pin 6 of the RJ45, and Pin 5 of the DB9 to Pin 4 of the RJ45. The other 6 pins of the DB9 socket and the other 5 connections of the RJ45 socket aren't used. You may need to cut off the unused connections inside the adapter so make sure you get the right ones.
3. A USB to DB9M RS-232 Adapter (Jaycar Part No:XC-4834 $39.00) if your laptop computer doesn't have an RS232 serial port on it. Otherwise you just use the RS232 port on your laptop instead of the adapter. Use the properties settings dialog box in Control Panel > System > Hardware > Ports > COM Ports to make sure the RS232 port is set to COM2.
You will need to cut off one of the RJ11 plugs from the telephone handset cable and get an RJ45 (CAT5 computer networking) plug fitted in its place. You don't use the two outer connections on each side, only the four inner ones.
Plug the RJ11 connector into the socket in the telescope hand controller base, and the RJ45 connector into the appropriate end of the wired up DB9-RJ45 adapter, plug the DB9 female connector into the USB-RS232 adapter's DB9 connection and finally plug the USB connector into the laptop.
You will need to download a small server applet called "StellariumServer" from http://www.geocities.com/scottpinkham/astro and install it on your computer, then get the latest version of Stellarium at
https://sourceforge.net/project/down...0.exe&84662567
Run the server applet, use the setup feature to make sure it is set up to talk to the correct COM port number on your computer (COM2) and accept the default TCP port number of 10000.
Next, you need to modify the config file for Stellarium so it knows a telescope is connected to the computer. Open it using Notepad to edit it, look for the following lines:
[astro]
flag_telescopes = false (change this to "true")
flag_telescope_name = false (change this to "true")
...
then at the very end of the listing add the following lines:
[telescopes]
1 = My_telescope:TCP:localhost:10000:50 0000
the first big number is the TCP port number which is the default value of 10000 and the second big number is the time lag in microseconds from when the telescope's position is read by the program (about 0.5 seconds) till when it is displayed in the Stellarium screen. The telescope name can be whatever you want to call it and is displayed on the Stellarium screen. To update the telescope's position press the Control key and the "1" key together.
You will need to align your scope first before you can use the computerised controls. Once done, if you then click on an object in Stellarium and press CTRL+1 the scope will slew around to the object. Now that's what I call computer control.
If you have any further questions contact me at robert_smeallie@yahoo.com.au
Clear Skies
Robster
Woy Woy, NSW
