Formulation of the problem

There is an amateur telescope with a simple mechanical focusing device. Focusing is done by rotating the focuser wheel. The focusing procedure (especially for the purposes of astrophotography) is quite painful (even using Pavel Bakhtinov’s mask and special focusing accuracy assessment software such as DSLRFocus or BackyardEOS), since:

• It is very difficult to apply the necessary effort with your hand and turn the wheel to a really small angle with precise focusing;
• Each touch of the focusing device causes telescope oscillations, which leads to a loss of waiting time until the oscillations subside and the result of the last iteration can be assessed (and the worse the mount, the longer the interval, the author had the pleasure to work with the mount, where the total attenuation period was ~ 20 seconds);
• The above features of the focusing process virtually exclude focusing in dynamics: rotation of the wheel with simultaneous evaluation of the result. As a result, focusing is an iterative process that requires a lot of patience and a certain skill that borders on art.

Based on the foregoing, we set the following task in general: it is necessary to connect an electric drive to the focusing device of the telescope, which will be controlled

• using remote control panel;
• "Remotely" from a PC;

In fact, the device is required to be able to rotate the axis of the wheel of the focusing device in a given direction with a given speed (both parameters are specified). Thus, the control panel must have at least two buttons (rotate clockwise and rotate counterclockwise) and the speed adjustment knob.

Disclaimer

I am not an engineer by education or by occupation. And even more so I am not a designer, mechanic or installer. In this case, it is a hobby that has grown around professional interest and curiosity. I do not pretend that this solution is optimal - it is quite possible a professional will immediately notice some things that could be made easier. However, I guarantee that:
')

• this solution works;
• anyone who knows how to use a soldering iron, a screwdriver, a screwdriver, a needle file, a tester and at the same time is an experienced PC user can repeat it;

There may be errors in the text of the program, the device diagram and specifications, something may not be done optimally - I will accept criticism and suggestions with pleasure.

This development (source codes, scheme, materials) can be used by anyone at will for personal, non-commercial purposes. Publication of materials is possible with reference to the source material and indicating the authorship.
This project to implement a focus on the Arduino platform is far from the first, you can find at least three more on the network:

1. http://sourceforge.net/projects/sglfocuser/
2. https://github.com/ejholmes/Arduino-Focuser
3. https://github.com/sirJolo/ascom-jolo-focuser

The first two do not develop and are not supported, but the last one is very interesting and appeared only after I completed my development in June 2014.

What happened

As a result, the stepping motor was selected and fixed on the focusing device, and the SD control device was developed and software was written to it:

• Fulling Motor FL42STH47-0806M, 12V, 0.8A stepper motor per phase,
  
  
• Focus control unit based on Arduino Uno microcontroller debug board and Polulu A4988 stepping motor driver in industrial case, power supply - 12V, 25 watts
  
  
• The control panel of a focuser, to work near a telescope without using a PC, has
  
  1. two buttons of the rotation of the focuser (yellow, continuous rotation at a given speed while the button is pressed);
  2. button to release voltage from the engine (blue, in case of overheating and in order to reduce energy consumption);
  3. speed adjustment knob;
  
  
  
• The focus control program from the PC (the control unit is connected to the PC via USB, the assembled version of the Focuser Control Panel (under Windows) is available here

Schematic diagram of the control unit and remote control:



The firmware of the microcontroller is laid out on GitHub , as well as the source code of the control panel.

Specification for all components available here . Components were purchased mainly in Russian online stores, prices are approximate. When ordering parts in China, the cost can be reduced by 2-3 times.

Ideas for the future

ASCOM driver

To automate the process of fine focusing it would be good to use ready-made solutions like Backyard EOS. For this you need an ASCOM driver, which I plan to do later.

Microfocusing

When using a Kreyford focus with a microfocus knob, the solution may differ significantly, although first you need to establish exactly whether the game is worth the candle? When using microstep, it is possible to rotate the axis of the foxer through an angle of the order of 3-4 '.

Replaceable filters

The next desire that arises after the mechanization of the focuser is the mechanization of the wheel of eyepieces and filters. This task has much more complicated mechanics and is beyond the scope of this project. However, there are projects that solve this problem. For example: ivastro.e3w.ru/FWF/index.htm

Wireless remote

There are various solutions that allow you to get rid of the wires. Or at least from minimize. There are ready-made solutions of the type IR remote control + SD control unit. I refused them, as in my case they have a number of drawbacks. For example:

• IR remote requires direct visibility, which is not always convenient;
• WiFi and Bluetooth modules for Arduino are quite expensive;
• For remote control it would be possible to use an I2C controller, reducing the number of wires to 4 and using a thin twisted pair, but the board with an I2C controller and peripherals will cost about $ 10.
• The ability to memorize position is very useful when changing eyepieces, with ready-made solutions this function can be difficult to implement.

Why is it done that way? How to make me?

A person who wants to use my experience and do something like this may reasonably ask questions about how to choose an engine, what kind of power supply is needed, etc. I will share the experience, but due to the volume of the material I will lay out in parts.

UPD: To be continued .
UPD2: the problem with the engine twitching when starting up was decided to be banal - if possible, do not use the 13th pin of the Arduino. The scheme is fixed, the firmware code on githubʻe updated.