View Full Version here: : Roll your own autofocuser

21-03-2016, 02:36 PM
I saw some others have had a go at putting together their own arduino driven focusers, so I've had a go with some success. Total price is probably under $100 and is mostly the stepper motor.

This is the one I built: https://sourceforge.net/projects/arduinofocuscontrollerpro/

I used the recommended configuration and had it up and running with almost no problems. Only thing is the stepper motor did get very hot, but I think that means I need to play with the DRV8825 board potentiometer to get the current right.

The actual stepper motor mount is one I modified from another design in Blender and 3D printed in ABS. It's for a Skywatcher 200P with the Nema17-PG27 stepper motor, and the design can be found on thingiverse.

So now I can control the whole setup from inside my house - nice. I'd highly recommend people give it a go if they want to save a bit of cash versus a commercial product, though factor in a reasonable amount of time to collect all the components and to put it together.

22-03-2016, 04:35 PM
Hello Marty.
Nice project, well done. Quite satisfying going the DIY approach I find.

I am finishing a similar project but mine is an Arduino telescope camera rotator. It works well but how do you make it ASCOM compliant? Does that require some specific coding? Would be nice to control it within Astro Photography Tool.
I am going to have a read through your pdf of the project and see where that takes me.

22-03-2016, 05:19 PM
Hi Jeremy,
I followed a project developed by someone else, so they'd written the ASCOM drivers. That's well beyond my abilities. Ultimately a focuser and rotator arent really very different though, so maybe you could repurpose a focuser driver if you programmed the arduino right?

26-03-2016, 09:14 PM
In the documentation it says about being compatible with the Moonlite stepper, does this mean, I can wire it up to suit the Moonlite Hi-res stepper and it would work? If so are there any wiring diagrams for this and has it been tested?

I have a Freetronic "Eleven" board which is 100% Arduino compatible, basically the same as the Uno board. Can the Stepper controller be modified to suit this board? I also use the Easydriver board for stepper control.

Freetronic Eleven website: http://www.freetronics.com.au/products/eleven#.VvZuUeJ97iw

27-03-2016, 09:29 PM
I just took the moonlite thing to mean it could effectively emulate a moonlight focuser. But I've not looked into it as I just run it as an ASCOM device. I don't see why it couldn't use a moonlite stepper motor though. You'd just have to work out which wire is which.

I also don't see why you couldn't use a Uno board instead of a nano. But nanos are only like $10 each. Just make sure you get the one with the right USB driver chip (I got the wrong one first time). It think it needs the CH340G chip?

27-03-2016, 09:35 PM
Okay thanks for the info, may give it a test, when I can.. I haven't got the moonlite motor yet but if the driver works it would be good to match them up. Not sure on the USB driver chip. I have had this thing working on a bipolar stepper with out trouble, but the resolution is way too course for a focuser, thats why my thoughts turned to the Moonlite hires stepper.


27-03-2016, 09:40 PM
The documentation goes through how to work out how many steps you actually need. I'm using the recommended hardware, which provides more than enough resolution for me with full steps. Plus you can use partial steps with the DRV8835 stepper driver to gain more steps if you want. I've had mine stepping on the bench well at 1/8th steps.

I've got the Nema 17 with PG27 gearbox, which provides approx 5400 steps per revolution with full steps. Seems typical to run it at half steps (so over 10000 steps per revolution). Plus as I said I've had it doing 1/8th steps, but I'm not sure how reliable it would be or how much torque.

27-03-2016, 10:06 PM
Well I had planned on getting the Moonlite hi-res stepper anyway, and it looks like the wiring is the same as the robofocus and the windings wont be that difficult to work out. I think they use pins 1, 4, 5 and 9 on the DB9 plug. I just didn't want to mess around with extra brackets etc on the moonlite focuser. Will see how it goes..

29-03-2016, 02:23 PM
I'm using the same arduino focuser project with a Nema17 PG27 stepper motor, however I went with the L298N motor driver. For software control, the ascom driver works well and I have mine integrated into my SGPro setup.

29-03-2016, 05:55 PM
Do you find the Nema17PG27 slow enough for focusing very small amounts? What is the reduction on that, I think I saw several different ratios.

Do you know of an Aussie supplier for the motor? I may give it a try...

29-03-2016, 07:25 PM
i find that it is okay. aussie supplier here: http://www.ebay.com.au/itm/27-1-Planetary-Gearbox-Nema-17-Stepper-Motor-0-4A-for-DIY-CNC-Robot-3D-Printer-/171836706736?hash=item2802440fb0:g: Hb4AAOSwiLdV8oCE

30-03-2016, 08:44 AM
PG27 means planetary gear 27:1 I believe. The actual ratio is ever so slightly less, but close enough.

For the steps you need to work out what is required for your system. It involves measuring how far your focuser moves for a complete revolution and the focal length of your scope. Then you can work out how many steps a particular stepper/setup will spend in the "critical focus zone". This is covered in the myFocuser documentation.

Hence what you need depends on your focuser and scope.

This is where I got mine from too.

26-06-2016, 03:34 PM
A mopnlite stepper motor should be pin compatible - there is a folder there on the site re moonlite compatibility - it has details on how to wire the rs232 connector be be moonlite compatible. And u can also use the moonlte focuser app or moonlite ascom driver


24-08-2016, 11:23 AM
Robert ,

I noticed that you are the author of the DIY focuser project in Source Forge. Its succesfull and represents a big effort on your part. Congratulations.

I am considering having a go at building one myself to mount on my Skywatcher Esprit 150.

A couple of questions ;

1. Why the Nano and not the UNO Ardunio Board ?
2. I cannot find any PC source code in the project downloads. Did you release the PC source code into the public domain ? and if so how can I download it .



26-08-2016, 03:33 PM
Space and cost - a nano + driver board can fit in a real small space, weighs little and can attach straight onto the focuser tube with velcro!

There is a UNO+L293D Motor Shield option.

Source code: This topic comes up from time to time. I use VS 2015 Professional with a number of other tools/plug-ins. Not too many people have that. And its get me into all sorts of bother trying to help others re publishing the .exe which I do NOT want to get into at all.

At the moment I am kept busy just answering some of the hardware issues and maintaining the firmware, there aint time for me to do much more than this. At some stage the source code may become available.