OnStep Controller

Convert older non-GOTO telescope mount to a modern GOTO with wireless communications and android application

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Telescopes consist of a telescope tube and a mount. In the old days the mount consisted of a knob by which you could adjust the scope to keep track with the stellar object's movement, or if you could afford it, a synchronous motor to drive the telescope east to west following the track of the star (call Right Ascension, RA for short). More recently, almost all serious mounts have stepper motors and microprocessors to control the RA movement ( and the north south movement called declination).
This hardware project is an Arduino shield board designed to mate to the Arduino MEGA 2560

The hardware provides the

  1. motor drivers (using TI 8825 ICs, two)
  2. connections to the motors, (separate RA and DEC stepper motors) 4 conductor Phoenix connectors
  3. Bluetooth communications (Microchip RN42 serial module),
  4. connections to the motor power supply (12-50 VDC)
  5. over current protection (Blade style automotive fuse)
  6. HAL effect sensor connector for periodic error correction detection (3 pin connector)
  7. limit switch input connection.

The software utilized by the hardware was developed by HD (the real hero of this project)

HD has written several software which are utilized.

  1. The Arduino MEGA 2560 runs the OnStep Software Git hub repository for the MEGA 2560 (written by HD a very talented individual )
  2. An ASCOM driver to make the mount compatible with any ASCOM supported software package (ASCOM page) and here is the driver HD's ASCOM driver page (including some great documentation)
  3. An android application for wireless control of the mount.

The controller can be controlled by a number of GOTO software packages such as Stellarium, and SkySafari. OnStep can use Serial0 and Serial1 on the the Mega2560. Serial0 is tied to the USB and Serial1 is tied to the Bluetooth module. The software supports the LX200 compatible protocol.

The BOM can be found on the Github repository.

  • simple events log

    steven.sagerian04/21/2015 at 18:31 1 comment

    10/14/2014 HD and I begin collaboration on hardware design based on his original work.

    11/14/2014 Shipped two revision A boards to HD for testing, kept two boards for my own testing and learning.

    12/30/2014 Began rev B boards redesign, incorporating all the bug fixes discovered on the Rev A revision.

    1/4/2015 Made rev B boards available to all cloudynights forum members interested in using the integrated board. Build 10 boards.

    3/2/2015 Last rev B aboard shipped to cloudy nights members.

    4/10/2015 Began Rev C board development, which will add onboard power supply (SMPS) to simplify power requirements.

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steven.sagerian wrote 05/14/2018 at 15:00 point

This project is pretty old. I am thinking about refreshing it with a smd version of the latest OnStep using the newer processor board and an ESP8622. I would also target the pcb to fit a specific off the shelf housing.  I recently did another design where I milled holes for the connectors on the top of the housing, that worked well. 

  Are you sure? yes | no

Daniel Zhou wrote 10/13/2017 at 13:55 point

Hi Steven,

Is there PCB file that could be opened? I am interested in your project.


  Are you sure? yes | no

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