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Arduino telescope goto for equatorial and alt/az mounts
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Align.h Enhanced error reporting Oct 20, 2019
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Validate.h Implemented spiral search May 26, 2020

OnStep Telescope Controller

Important Note


  • The RELEASE BRANCHES are well tested and what most should use. Usually the newest (highest revision) RELEASE is recommended. No new features are added and only bug fixes where necessary and safe.
  • Tne BETA BRANCH, if present, is a "snap-shot" of the MASTER where we have reached a point of apparent stability. This provides access to most new features for adventurous users.
  • The MASTER BRANCH is the most up to date OnStep version; where new features are added. It is the least well tested branch and should only be user by experienced users willing to test for and report bugs.

What is OnStep?

OnStep is a computerized telescope goto controller, based on Teensy or Arduino control of stepper motors.

It supports Equatorial Mounts (GEM, Fork, etc.) as well as Alt-Az mounts (including Dobsonians, and the like.)

OnStep was designed, from the beginning, as a more or less general purpose system and provisions were made in the firmware to allow for use on a variety of mounts.


OnStep supports a wide variety of connection options. Either two or three serial "command channels" can be utilized. One of the these is normally devoted to a USB connection and for the other(s) choose from the following:

  • Bluetooth
  • ESP8266 WiFi
  • Arduino M0/Ethernet Shield
  • Even another USB port or RS232 serial isn't very difficult to add.

Other software in the OnStep ecosystem include:

  • an ASCOM driver (with IP and Serial support),
  • an Android App useable over WiFi or Bluetooth equipped Phones/Tablets (version 2.3.3 or later),
  • a "built-in" website (on the Ethernet and/or WiFi device),
  • a full planetarium program that controls all features (Sky Planetarium).

OnStep is compatible with the LX200 protocol. This means it can be controlled from other planetarium software, like: Sky Safari, CdC (even without ASCOM), Stellarium, etc.

There are also INDI drivers so it can be used from Linux, with CdC or KStars.


Detailed documentation, including the full set of features, detailed designs for PCBs, instructions on how to build a controller, how to configure the firmware for your particular mount, can all be found the OnStep Group Wiki.

Change Log

All the changes are tracking in git, and a detailed list can be accessed using the following git command:

git log --date=short --pretty=format:"%h %ad %<(20)%an %<(150,trunc)%s"


Questions and discussion should be on the mailing list (also accessible via the web) at the OnStep Group.


OnStep is open source free software, licensed under the GPL.

See LICENSE.txt file.


Howard Dutton

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