celkins

Taken early this morning - 5x15s frames, live stacked in SharpCap4, C11+Hyperstar & ZWO183MM

Ok for me...

An absolute position focused can never go negative - what does it mean to be further in than "all the way in" (i.e. at zero) ? You really should start fully wound in, and then track out to focus under software control, so that it knows your real position, not just some arbitrary starting point, as would be the case with a "relative position only" focuser... Clear skies, Carl

I don't have the same setup, but I opted to use a NEMA 17 12v/200 step stepper from the off - over engineering, maybe, but it's been a fun project, and gives very precise control via the fine focus knob, which is good for my Hyperstar setup due to the very narrow CFZ. This certainly doesn't lack torque.

In essence, yes, correct - as long as you accept the same commands from the driver, and return the expected return codes, then it won't see any difference: my implementation uses an Adafruit motor shield to provide micro stepping control. It should *run* okay on an uno (I'm using an uno clone), but a "universal" sketch would be difficult due to the number of possible hardware variations - your motor board is different to mine, are both different to Dave's (IIRC). You should need minimal changes as you outlined above to implement your own clockwise & anti-clockwise routines, using step(1) and step(-1). Ask here if you have any problems...

I think the most significant thing, here, is whether the focuser declares itself to ASCOM as "absolute " - implying that it keeps a notion of an absolute position, or whether it's "relative" - in which case all motion is relative to where you are at the start, wherever that may be... My variant on this uses non-volatile memory to store the stepper position regularly, and declares that it's absolute; it sounds like you support relative motion, at the moment, Dave, which is perfectly valid, and in some ways a more logical thing to do, since then any changes outside of the driver (manual movement, for example) don't matter. This is an excellent thread, a super example of collaboration, and thanks to all.

I2c bus - with a repeater from NXP ...I'm also using i2c for a couple of temp sensors, to control a 40mm fan on the stepper heat sink - without cooling, it gets rather hot when position holding, but it's prone to jump if I de-energise the coils.

I just read the sensor directly, calculate the dew point, and report it on an LCD that I've attached; that will be located in my warn room.

Yet to test how effective automatic temp compensation is, but theory suggests that for my setup (C11/HyperStar), with its tight focus requirement, it's probably worth while. I also chose to use a sensor which reads humidity, so that I can keep an eye on how close I am to the dew point... Good thread, everyone, and thanks, Dave, for inspiring me to build an auto focuser.