Christmas (arrrrrh!) Project - part II (the focuser comes!)

[Stargazer33]

Please excuse the title - I think nursey has been upping my medication again!

For my Christmas holiday project this year I was thinking of making an arduino focuser. I have been reading a few threads on here and thought it would be a good project to keep me out of the sherry trifle for a day or two!

I was looking at these stepper motors on the internet today and was wondering if A: they are the correct type of motor and B: if so, does anyone know the diameter of the shaft so that I can order the drive pulleys to fit them?

Also, is there a good kit of parts that I could use to make the focuser and is there a supplier that people like and have had good service from?

Finally is there a book that you would recommend to get me going on the programming?

Sorry for all the questions, but I would like to get everything organised before I start buying the wrong stuff.

Thank you in advance.

[hobsey]

What scope will it be going on as we need to know where abouts its going to be placed.

[Stargazer33]

It will be going onto a Revelation Superfocus 2-inch SCT Rack n Pinion Focuser which is attached to my C8 XLT.

[themos]

Have a look in this yahoo group http://groups.yahoo.com/neo/groups/sgl_observatory_automation/conversations/messages they have lots of info on how to build one. 

[Gina]

I use those stepper motors - the shaft is 5mm.   I use timing pulleys and belt to drive the focuser.  You can get plastic timing pulleys from motionco with 3/16" bore which are a nice tight fit on the stepper shaft (not always in stock though and then it's up to 4 weeks delivery).  They sell the timing belts too - go for MXL size for pulleys and belts.

[Stargazer33]

Have a look in this yahoo group http://groups.yahoo.com/neo/groups/sgl_observatory_automation/conversations/messages they have lots of info on how to build one. 

Thanks Thermos! I will have a look at that over the weekend.

I use those stepper motors - the shaft is 5mm.   I use timing pulleys and belt to drive the focuser.  You can get plastic timing pulleys from motionco with 3/16" bore which are a nice tight fit on the stepper shaft (not always in stock though and then it's up to 4 weeks delivery).  They sell the timing belts too - go for MXL size for pulleys and belts.

Thank you Gina, that is good to know. I'm glad I am on the right track. You are a font of knowledge as always. 

I have been reading your thread about your Arduino focuser and it seems that everyone runs their focuser from a PC or laptop. I was hoping to have a stand alone unit that I could use if I go visual; I don't really want a laptop screen killing my night vision. Can you run the Arduino focuser off of a 12v dc supply only with manual buttons in a control box, or can it only be controlled via a computer?

[themos]

It's very easy to rig up a manual control for a unipolar stepper motor. I just bought a 12 position rotary switch and connected each pole to A-B-C-D-A-B-C-D-A-B-C-D where A/B/C/D are the four windings of the motor in just the right order to make the motor run.  

[Gina]

I don't actually run my Arduino controlled focusers from the computer ATM - I haven't looked at the interfacing as yet.  I use a control box in the warm room with 5 buttons.  The outer ones provide a fast forwards and backwards for coarse focussing.  Next in move the focuser one focus step whilst the other one moves back 10 focus steps.  A focus step is not necessarily one stepper motor step but the smallest amount of focus change that can be detected and may be several stepper steps if the drive has a high reduction ratio such as when using the fine focus knob on the telescope's focuser.  The reason for the 10-back function is that you can go past perfect focus by a few steps and then back-10 and go forward again counting the steps.  The reason for approaching perfect focus from the same direction every time is that there will probably be backlash in the reduction drive (eg. with the mini steppers with 64:1 gearbox).  This gets round the problem.

The electronics of the control box is just a resistive divider fed from 5v, providing a DC voltage which is fed through a wire to an analogue input on the Arduino.

[Stargazer33]

That's great Gina, thanks!

I was hoping that I would be able to have a 'stand alone' system that didn't require the laptop to control it.

I have a mains power box (last years Christmas project) with spare 12v DC outputs. I can convert one of those into a 5v DC feed to power my focus control box. Would a simple resistive divider work for that, or would I need to build a proper power regulator similar to the Chinese LED dimmers that have been used to control dew heater bands?

[themos]

For a 12v to 5v DC-to-DC converter you could have a look at eBay item number: 180669621759

I haven't tried it myself but it's very popular with remote control model makers.

[Gina]

If it's a regulated 12v supply then, yes, you could simply add another resistor at the top like you say. 

[Stargazer33]

For a 12v to 5v DC-to-DC converter you could have a look at eBay item number: 180669621759

I haven't tried it myself but it's very popular with remote control model makers.

Thanks for the heads up Themos! That looks like a really neat little solution.

If it's a regulated 12v supply then, yes, you could simply add another resistor at the top like you say. 

Yes it's a regulated 12v 3A SMPSU - probably a Chinese copy of the Meanwell ones, but it works at the moment!

[themos]

I don't like the dividing resistors idea because they can't deliver much current without wasting a lot of power. Isn't it the case that all the current that will pass through your 5 Volt load must also pass through the top resistor of the divider and that top resistor must see a 7V drop. If you need 1 Amp, you consume 5 Watts of power and waste (at least) another 7W on that resistor. 

[Gina]

The input resistance of the Arduino is extremely high and I use a current of about 1mA down the resistor stack.  So resistors of 1K x 5 plus 6K8 from the 12v supply or more if the supply is higher.  A resistor to Gnd of 100K or a bit less will give 0v with no button pressed (OFF).  A 10nF ceramic capacitor at the Arduino end stops any interference pickup getting to the input.  Incidentlly, I use switch debounce code in the Arduino sketch to avoid multiple pulses being generated instead of one.

This system has proved relaible in spite of there being about 4 metres of unscreened wire (bell wire) from the control box in the warm room to the Arduino mounted in a box on the scope.  I would, however, recommend using screened cable rather than bell wire - I just used what I had available at the time

[Stargazer33]

I've had a look on the web and have found a couple of schematics that I like the look of: KCOTARs one and YESYESs one in his very nice power distribution box.

I very much like the simplicity of the yesyes motor focuser, but would like to control it via push buttons when doing purely visual, hence I would like to combine the two.

I was wondering what programmes (preferably free! ) people use to sketch out their schematics?

So far I have bought for this project:

Arduino Nano (compatible)

Arduino Uno (compatible)

Easydriver Stepper Motor Driver.

Enclosure

Prototyping Board

Red Neon Light Round MOM Push Buttons

5v Stepper Motor

Drive Belt and Pulley

I will order the relay etc for the yesyes build later. Wire/Cable I may recycle from work or just buy new nearer Christmas. Oh and I need to get some ali plate to mount the stepper motor onto the focuser (don't know how I am going to do that bit yet as there isn't anywhere to drill any holes!) and I think I will get the DC/DC converter that themos suggested above to drop the 12 volts from my power supply box to 5 volt to run everything.

My intention is to put all the boards in the enclosure (handset) and then to run the power cable from the supply to the handset and then another cable from the handset to the motor. The handset can then be velcro'd to the tripod when not in use or when I am controlling from the laptop via a USB cable.

Hopefully I can 'adjust' someone else's script to run everything. If not, I have asked for 'Arduino for dummies for Christmas'!

[Gina]

I use XCircuit for circuit diagrams and other 2D drawings on my Linux box.  Several libraries of varoius electronics symbols and others are included so you don'y have to create your own from scratch.  It's what I use for all my 2D diagrams on here.  For 3D drawings I use SketchUp.

[Stargazer33]

Thanks Gina! I did see XCircuit whist I was hunting for a programme but thought it was only for Linux systems. Following your link it seems that you can use it on Windows based systems too.

I will give it a try and hopefully post my intended schematic.

[Gina]

Thanks Gina! I did see XCircuit whist I was hunting for a programme but thought it was only for Linux systems. Following your link it seems that you can use it on Windows based systems too.

I will give it a try and hopefully post my intended schematic.

Yes, I thought it was Linux only or at least linux and Mac OSX only.  I looked for it on Google for you and found it   I too noticed they covered Windows too now and that it has been updated.  Last time I looked a few years ago it was not being developed any further so I have you to thank for looking and finding a newer version   I'll download the latest version and see how much it's improved   The version I'm using has a very odd user interface

Another point of interest is that it's developed in Python which is the programming language I've been using in Linux.  It can be cross compiled for Windows too.

[themos]

Fritzing?

[Stargazer33]

Yes, I thought it was Linux only or at least linux and Mac OSX only.  I looked for it on Google for you and found it   I too noticed they covered Windows too now and that it has been updated.  Last time I looked a few years ago it was not being developed any further so I have you to thank for looking and finding a newer version   I'll download the latest version and see how much it's improved   The version I'm using has a very odd user interface

Another point of interest is that it's developed in Python which is the programming language I've been using in Linux.  It can be cross compiled for Windows too.

Glad to help Gina! Never thought I would be saying that to you!!! 

Something not quite right with the version I downloaded as I can't get a line to appear all the time. The circle and square tool don't seem to work either! 

I may try to download one of the other versions, but in the meantime I have found an old copy of CorelDraw 8 that I had and will use that just to get something on paper as I think I can remember how to use that from...cough, cough years ago! 

Fritzing?

   

[themos]

 http://fritzing.org/download/

[Gina]

I see - I think   I'll look into it more deeply when I have time.  One of my duties when I was employed in the Civil Service in an R&D department was teaching new entrants computer programming and electronics generally.  This meant taking things right down to the basics and explaining in simple terms.  Later in life I gave a series of talks in my own home to a small group of ladies of our local Women's Institute as an introduction to computers and how to use them.  A couple of the ladies went on to more advanced courses and obtained qualifications in computing.  With the advancement of computers in farming, this was very useful to them (we live in a farming community and are smallholders ourselves).

[Stargazer33]

Ahh! Okay, that looks really interesting. As Gina said, I will look into that when I get more time - I suppose work must come first!   Thanks for the link themos!

I think I am going to need a LOT of very basic explanation of programming before this project is complete - hence the Arduino for Dummies for Christmas. 

The nano and uno copy boards have just arrived at work. Along with the prototype board, enclosure and drive belt & pulley. Somehow I can't see me waiting until the Christmas holiday to start this project!   Patience never was one of my virtues. 

[Gina]

I think Arduino for Dummies was one of the books I bought when I started with the Arduino.  Later I bought the Arduino Cookbook for more advanced info.  Very good

[Stargazer33]

Thanks Gina, that's good to know. I did wonder if A4D would be a bit too basic and not have the information I needed, but I need to start somewhere! 

I will have a look at the cookbook too. Hopefully Paul Hollywood isn't in it or I will never get it off my wife!