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Build Cheap Digital Setting Circles
Submitted: Wednesday, 30th May 2007 by Martin

This article will describe a cheap option to build digital setting circles. First off, I am not affiliated to any of the sources I got the parts from and I am not getting commission from them.

Lets start with what we need:

  • A: Dave Ek’s circuit board and description found at  DigiCircles
  • B: The circuitboard from Farcircuits 
  • C: The encoders from ebay or anywhere else. My two encoders where $60.31 for two including postage from this ebay store  but as i said you can use any you like.
  • D: A cheap laptop, mine came from ebay and was $41.00
  • E: A serial cable to go from the box to the laptop. (I am still trying to interface the box to my pocket pc, as soon as that works I will be a happy chappy). The serial cable is about $16.00 from Dick Smith.
  • F: some hardware, total cost was $20.00 approx because I already had the bearings for the encoders.

In total the cost will be:  

Circuitboard $40.00 
Encoders      $60.31
Laptop          $41.00
Cable            $16.00
Hardware     $20.00
-------------------------
Total             $177.31

If you have a laptop it will be cheaper again.

image002.jpg

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4000 pulses per revolution encoders

When you use these encoders you will have to fit an bearing of the right size. The bearings I used are 629rs and will fit an 8mm shaft.

The tricky part is to fit everything straight so the encoder wheel wont hit anything inside the casing. Once done it will look like this:

image003_[800x600].jpg

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Encoder

The encoder can be mounted any way you like. I have used ¼ to ¼ threaded hollow rod. But you can use anything that fits.

The GSO dob I used it on has an alt shaft that is very close to 8mm thick so it was an easy fit after I took the knob of the end.

Fitting the encoder so it doesn’t move is easy done by bending a thin piece of plate steel and then fitting it to the encoder and the dob side panel. But remember it has to be removable for when the dob has to be disassembled.

image005_[800x600].jpg

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Even when hanging free it will work, but a rigid mount makes it more reliable

For the az mounting you can do the same as long as the bolt thru the board is securely fastened to the lower board. Example follows below.

image007_[800x600].jpg

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Az encoder mounted on the base board

As every scope is slightly differend in height I cant give detailed information on fitting the encoders, the type of mounting I used is for the 10” GSO I have but should work on most dobs.

Now for the electronics.

This is the easy part except for connecting the encoders (it all depends on where you get the encoders from). When you use the argonavis encoders it is easy to fit to the circuitboard, it is sort of made for them.

For the encoders I have used I had to search long and far for the specs and wire layout.  The pin layout is as follows:

  1. Channel A
  2. Vcc
  3. Ground
  4. NC
  5. NC
  6. Ground
  7. Vcc
  8. Channel B
  9. Vcc
  10. Channel I

Note: all the Vcc's and Grounds must be connected, they function as noise suppression. For other encoders you are on your own.

Moving on to the circuitboard.

When you order it from FarCircuits it will have the programmed pic and everything else except the resistors and capacitors, you can get them from any electronics shop. It is easy to fit in a jiffy box as shown below (left picture).

I just used some old mouse cables to connect the encoders to the box as seen in the right picture below.

image009_[800x600].jpgimage011_[800x600].jpg

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Electronics in the jiffy box

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Connecting encoders

The battery clip shown is going to a 12V battery.

To assemble the Dave ek box goto DigiCircles,  a full explanation is on his site. If you don’t know anything about electronics you could ask someone to build the circuitboard for you.

The program you can use to read the output is Digital setting circles  and many astronomy programs, but with most astronomy programs you will have to use the Ascom platform and ekbox.exe. These can be obtained from the software page.  Also there are full explanations on how to use the files in various astronomical programs.

Coming to an end in this article, anyone can build this and make it as cheap as they can.
It works perfect and is an pleasure to use.

Article by Martin (mill). Discuss this article on the IceInSpace Forum.
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