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I thought I would do an update in case anyone else wanted to try and do this. My advice would be DON'T - there are much cheaper ways of doing it than using the HSM20.
I initially went down the non-DIY route first and got the HSM20 and a HitecAstro Mount Hub Pro V4 as the advertising states "Feather touch focusers can be used with a current limiting adaptor", I also confirmed by email with them that it would work. Long story short - it doesn't which left me with an expensive paperweight. Apparently it was my fault as the MHP V4 website also states "Compatible with any unipolar stepper motor" and the Feather touch HSM20 is a Bipolar stepper motor. Anyway, enough sour grapes and moving on.
I put together an Arduino based controller (MyFocuserPro 2 by Robert Brown) and it works a treat in testing. I just need to put together a box for it to go in and I'm done. With my 2" draw tube I had to set the max limit to 50,000 (default is 10,000) steps but this gives me a very smooth control over the full range. A 5 Volt supply seems to work best on it.
The pinout on the HSM20 RJ45 is as follows:
Pin 1
Pin 2 - Not Used
Pin 3 - Winding A-
Pin 4
Pin 5
Pin 6 - Winding A+
Pin 7 - Winding B+
Pin 8 - Winding B-
I'm still testing but I believe pins 1, 4 and 5 are the thermocouple - I will update when I work it out.
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