I have received a request to describe the autoguider electronics a bit better so I went back and opened my controller box and drew out the circuit.
Link to a pdf page with circuit diagram: Circuit Diagram of DIY Autoguider Ver 2
There are a few tricky issues with the circuit:
1. Polarities: The RA direction is sometimes confusing to get right but it is easy to do a test and swap two connections around or tweak the Arduino code to correct it.
2. ST-4 connection to laptop parallel port. Many laptops do not have a parallel port anymore. I used an old laptop I had available. You probably do not want to use a new laptop outside in the dew anyway…
3. Stepper motor; I used a stepper motor with microsteps (1/16th steps). This makes the tracker/ guider movements smaller and less jumpy. Similar to a much larger ratio gearbox.
4. The tracking speed can be calculated and programmed in easily. I found that my calculated stepping rate was spot on and well within the autoguider’s range to correct without working too hard.
5. I used a webcam based autoguiding camera that I modified myself. You can probably use any autoguiding camera, or if you want to try, modify your own webcam to fit on a suitable lens.
For more details, look at previous posts with the same title (Parts 1 to 4). A copy of my latest Arduino code is also available.
If you need or want more information, please ask, I will do my best to answer quickly.