SkyMap Pro Driver for DSC Project


In order to use the DSC with SkyMap Pro a driver is required to be written. The driver is the part of the program that 'Talks' to the DSC board via the serial port of the PC.

This allows the DSC to be initialised and interrogated about the telescopes current position. This position is then read by SkyMap Pro and shows on the map as a crosshair at the telescopes current position in the sky.

The driver I wrote was written in C++.


Command Set

I modified the original PIC code to add a new command. The complete command set I used was:


R[RA Ticks] [Dec Ticks]           Already existed


Q                                             Already existed


S[RA Pos] [Dec Pos]                 New command

The R command tells the DSC the number of ticks (steps) that the encoders have for a single revolution. In my case both axes had a count of 8192 so the command sent was:

R8192 8192

The Q command is used by the driver to request the current positional information.

The S command will tell the DSC where it is currently pointing and to set the positional information to the data following in the command.


Setup Dialog

Part of my driver includes a setup dialog box that allows the user to enter the tick counts for RA and Dec. It also is used for aligning the telescope by selecting a star from a list, pointing the telescope at it, and then telling the DSC that is where it is looking. This process MUST be carried out at least once before the DSC will start to give positional information.

To get to the dialog box select the Telescope menu option in SkyMap Pro and choose Configure. This will bring up a SkyMap Pro dialog box showing all of the telescope drivers it has access to. Select the required driver from the list and click Configure.


My setup dialog box is shown below.

As can be seen the tick counts may be entered if desired. These values are stored in the Windows registry and therefore only need to be entered once as they are retrieved from the registry each time they are required.


Star Alignment

In order for the star alignment to work correctly the telescope MUST be polar aligned. Other DSC projects tend to use a minimum of a two star alignment process, which means that the telescope does not need to be accurately polar aligned.

This process may work very well but in my case I want to do some long exposure Astro-Photography and I only have an RA motor to track the stars so polar alignment is a requirement. As the scope is polar aligned anyway it is really a two star alignment process, first the pole star and then the star from a list.

Selecting the Star Alignment button of the setup dialog box will take you to the star list dialog box.

Select the star to align to and click OK. A message window will be shown.

The message window displays the star name and the values for RA and Dec positional information that will be sent to the telescope, using the S command, once the alignment process has been completed.

Simply centre the selected star in the eyepiece of the telescope and click OK. The driver will now tell the DSC where it is pointing and the crosshair on SkyMap should be over the same star.



If your telescope has an RA motor to track the stars then the crosshair should remain over the star. If not it will drift, just as it will drift in the eyepiece.

Once the telescope has been aligned in this way it is simply a matter of releasing the RA and Dec clamps, moving the telescope until the crosshair is over the object that you wish to observe, securing the clamps once more and look in the eyepiece.

99% of the time I have the object in the eyepiece. If not it isn't far away.


Driver Download

To download the driver click HERE. The file needs to be placed in the directory 'Drivers' from the main SkyMap Pro directory. Once this is done the Configure Telescope dialog box will display the driver in its list.

Although I have given the driver the name for my particular telescope it will work for any scope using the DSC project discussed elsewhere on the website.


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Copyright 2004 - 2007 Phil Davis


Last updated 2nd December 2009