The Alpaca digital setting circles driver (alpacadsc) allows connecting client software like planetariums to ALT/AZ mounted telescopes like dobsonians with the appropriate hardware. The software supports tracking the position of the telescope as it is moved across the sky, allowing easy acquisition of sky targets.
The basic theory of operation is for the user to locate a sky target such as a bright star and center the telscope on the target. Then using the planetarium software the user send a “Sync” command to the driver with the coordinates of the target. In Cartes du Ciel, for example, the user would right click on the target and select “Sync”. This tells the driver where it is currently pointing in the sky. Using the configured latitude and longitude and the current time alpacadsc can then compute the altitude and azimuth of the target. From this it can then compute the altitude and azimuth of the telescope from the changes in the encoder values.
This simple “1 star” synchronization works well over a small part of the sky (say 30-50 degrees) as long as the telescope is fairly level. If you find the pointing of the scope is poor as you get farther from the original sync target then simply sync on a new target closer to your desired desination target. This should improve the pointing accuracy. Do this as necessary as you move around the sky.
Before using alpacadsc it is necessary to configure a profile for your telescope. This an other usage details are covered in the Usage section.