Arduino Focuser

I wanted to make a focuser for my Orion Astrograph 8 inch reflector using an existing  Indi Library driver for Kstars/Ekos.  It had to be  simple and I wanted to avoid writing a  new driver for Indi Library.  During my research, I found some documentation for JMI Smart Focuser that explains the command set.  This seemed like an easy solution using an Arduino and a stepper motor.  I then reviewed the Indi Library source code to find out what calls the JMI Smart Focuser driver is  making to the  focuser. Seeing that the Smart Focuser driver was making minimal commands to the JMI Focouser, I decided to create my own simple focuser using the Arduino Nano.

Arduino Focuser

First Version

My first version that I built used  a separate Focuser controller which plugged into the remote stepper motor assembly.  This used an LED display and had a hand controller and powered by a separate 12V power supply.  I found that I never really utilized the display focus buttons, so I simplified the focuser design.

First Version
First Version

Second Version (Simplified Version)

The minimal Arduino  Focuser  uses  a Nano Arduino and  is powered by the USB connection.  There are no other external connections.   It plugs directly into my Indi server’s powered hub. (I have also powered it from my ZWO asi178mmc camera using its  built-in USB hub).

Parts List – for Simplified Version

  • Arduino Nano
  • ELEGOO 5 sets 28BYJ-48 ULN2003 5V Stepper Motor + ULN2003 Driver
  • Protoboard (for mounting the Arduio Nano and Stepper controller)
  • Aluminum GT2 Timing Belt Pulley, 16 Teeth Bore 5mm with 6mm
  • MXL Belt 76MXL/B95MXL 6mm Width 2.032mm Pitch
  • RMP .063 3003 H14 Aluminum Sheet, 12″ x 12″

All above parts  are available online via when this article was published.

Below is the layout of the simplified focuser that includes the electronic parts layout and wiring:

Focuser II – Completed Module
Focuser II – Backside

Bracket Assembly

Below shows the Mounting Bracket for the focuser board and stepper motor.  Note, you will need to add the mounting holes of the stepper assembly and oblong these  holes for adjustment purposes.  The MXL belt is perfect for the Orion Astrograph focuser and will slide on and off the fine adjustment knob.  Here is a pdf file of the assembly:   Focuser.pdf

You should be able to print out the file and make a direct template. All units are in millimeters.


I have included both schematics for the first versions and the simplified version.  

First Version Schematic Diagram
Simplified  Focuser Version Schematic Diagram

Arduino Code

The Arduino code (Version 0.60) is provided in a zip file.  It has been complied using Arduino IDE 1.8.5.  I have included the stepper accelerator library in the zip file that I used for this version.  For more information regarding the stepper accelerator library,  follow this link:   Accel Stepper Library

The code supports both versions and by default the displays are commented out for the simplified version. Here is the zip file:  Arduino Focuser V0.6 zip

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