Aaron Turner built his own digital setting circles (DSCs) to add to his 12″ Dobsonian telescope after finding the commercial options were pricey and lacking in a good user interface.

DCSs show you where to point your telescope to locate your astronomical target.  They are particularly useful in areas of high light pollution.  You can read more about them here.

Powered by a Teensy 3.1, Aaron’s digital setting circles allow connecting
your computer, iPad or Android device to your telescope via WiFi to
more easily find any object in the night sky.

More information on the project can be found on the Teensy-DSC Wiki.  The code for the project can be at TeensyDSC on GitHub.