One of the perennial questions that gets asked is “I want to add some kind of computer connection to my telescope to help me stuff in the sky”. There’s a lot of information on web on now to do this and there’s probably nothing terribly new here apart from the fact it’s been gathered into one place.

If you feel that you can strip the insulation off a wire, cut things with  scissors and are able to copy files from one place to another, edit a text file and install devices on a PC, you’ll be able to make this project.

What follows is a simple step by step guide to building a gizmo to that connects via a USB port to a PC, connects to telescope encoders and provides a way for popular software to know where the telescope is pointed in the sky.

Ok, first the bad news. It’s not designed to control the movement of the telescope or provide “GOTO” capabilties.  While I cover the details and workings of the encoders – the bits that sit on your telescope – I won’t be going into the installation of these. It does require a PC, but as notebooks especially are cheap, portable and have better battery life, this is not a major drawback.

It does , cost less than $50, requires no soldering and you can buy all the parts you need from your local Jaycar store.

In a second article I’ll also be covering adding in a Bluetooth connection to allow use of Android or iPad/iPhone devices.

Background information or how it all works.

Encoders

Encoders are at the heart of the system. You need two per telescope to go on each axis.  One to measure how far the up and down (ALT or Altitude) and one to measure how far it’s been moved around is’s base (AZ or Azimuth). For equatorial mounted telescopes – those that are set up to follow stars by moving in only one axis they’re refered to as Declination (DEC) and Right Ascension (RA). These encoders produce a number of “pulses” or “steps” per revolution. Common options are 2000,4000, 8000 or 10000 per 360 degree revolution. (I go into encoders and how they work here.)

An important thing to remember is that the encoders cannot measure the actual position of the telescope, only how far the telescope has moved and in which direction. So for example you have a telescope with 4000 step encoders and move it from being pointed level at the horizon and move it 90 degrees so it points straight up at the zenith, the encoder will send out 1000 pulses.

If we’d told the PC that the telescope was pointed at the horizon ( or 0 degrees AZ) and the pulse count is now 1000, knowing the encoders have a 4000 pulse resolution, it can easily calculate the scope is not pointed 90 degree “up”.

You can obain encoder kits or fitting details for almost any telescope type on the web or you can easily build your own once you have the encoders themselves.  Most of these use the encoders from US Digital such as these.  A number of projects have reported success with the cheaper capacitive AMT Encoders.  For dobsonian telescopes encoders are often mounted with an arm that allows the rotation of the the telescope to be properly recorded.  Other telescope type such as older fork mounted SCT units require more complex mounting hardware.

In the example we’ll be using here, the Meade LX50 telescope already had encoders installed.

The Arduino

Over the last few years there’s been an explosion of small cheap, small, powerful computers that help experimenters and hobbyists product a vast variety of cool projects and gadgets. Unlike a normal PC, they can normally connect to LEDs, motors, sensors and other devices to both read from and control devices.

The Arduino is about a the size of a credit card and in this project handles the task of working out how far the telescope has moved by counting the pulses from the encoders. It connects to the PC via a micro USB cable and to the encoders via eight wires (4 per encoder). It also needs a small amount of code to be loaded onto it. But don’t worry, there’s a range of easy to use tools to make this happen!

Encoder Wiring

Each endc

ASCOM and other software

Things you need

Putting it together

 

Weight	3kg
Size	142x129x257 mm
Battery Life	6 Hours
Aperture	50mm
Lens Type	Triplet apochromatic optics (APO)
Focal length	250mm
Sensor	Sony IMX462
Image Format	MP4/AVI/TIFF
Resolution	1920 x 1080
Wi-Gi	5G/2.5G