Stepper motor focus control version 2

[Reggie]

Hi Ringz, I appreciate the thought The LCDs that we are using are designed to fit straight into the arduino boards, no soldering required at all. If you see one compared to the NKC one you can see why they are more desirable.

I'm sure we will provide information to build something similar to what we are using so I'll bear in mind the RGB LCD link that you've posted.

[ncjunk]

Quick update...

I have a version of software for the Arduino board and a version of Visual Basic 2008 on the PC which is now communicating and controllable from Maxim DL by setting the steps and then clicking IN or OUT.

Next step is to tidy the code up as I overdid some bits where I didn´t know what I was doing...basically....

So it is only really using the move function but I now need to add in a bit more functionality.

I now need to get the stepper hardware working properly as the Motor keeps stalling (need a separate power supply but it doesn´t seem to work properly when I attach one).

But hey by Christmas it should be working!

Neil C

[George]

Thats great news Neil, my Freeduino board arrived today. Just got to get a stepper motor and build a driver then Im rocking

[Reggie]

Nice one Neil, slightly odd about the stepper circuit though.....

[ncjunk]

Yep, I need to add some diodes and a couple of capacitors (I think). The diodes I have but the capacitors I have yet to buy....got a fine for using a hands free telephone so am a bit skint at the mo....

I will post a version of the software this weekend for people to correct!

Neil C

[Reggie]

Got any old tech knocking around neil? Old PCI cards, motherboard etc.? Lots of salvagable caps on those....

[ncjunk]

aahhh good point I have loads around the place I never thought of that...

[Psychobilly]

Fine for using a hands free.... boy those spanish police must be.......

[ncjunk]

They dont like it! it is illigel and they are thinking of doing the same with tomtoms. but I didn´t try to hide it and apologised, made a bit of a comment about myself being a stupid English person and after that they were quite nice. I always feel it is better to come clean rather than winding them up and making it worse.

NC

[themos]

Hello, I have a DIY motorised focuser using a stepper motor (4-wire unipolar, I think). I control it manually with a rotary switch that energises each coil in turn. I would like to turn it into an ASCOM focuser over USB. Any ideas? Is an Arduino board what I need?

[ncjunk]

I would more say that it is what you COULD use if you want to...in principle we are still playing. I have an ASCOM driver almost working and the Arduino software written but the last month has been difficult to find time to finish it so lacking some testing.

I am using the Arduino board with a 293D driver chip attached to the stepper motor. It all works on the bench but I am lacking a bracket to attach to the telescope..Also I need to add a gear box.

So yes you could buy an Arduino off of Ebay and attach a driver circuit (I believe there are Arduino stepper driver modules available??). The Arduino has a routine to control the outputs to the coils in the same way you are using the switches at the moment.

If you know any programming that would be usefull, you could help improve the code we have.

Neil C

[themos]

Thanks!

Is this

Motor Shield - Arduino motor/stepper/servo control

the kind of thing one needs on top of the Arduino?

Does the Arduino need power on top of the USB 5V? I know that the motors will need separate power (12V from the powertank is fed into my manual control box).

[ncjunk]

yep thats the kind of thing. the 293 chip provides 0.6 amps so check your motor does not run off more than that.

if usb is connected all the time then only that and the 12v for the motors is required.

if you make it stand alone and use an lcd then you can use a separate 5v supply instead of the usb.

NC

[themos]

I've ordered an Arduino, my motor is rated at 0.26A/12V per coil (a Mitsumi M42SP-7 with 7.5deg steps) and I'll have to see if I can get the L293D or some other chip.

[ncjunk]

Cool, I am tempted to get that motor shield now and have a play after xmas.

NC

[themos]

I bought the last 2 Darlington array chips from my local Maplin store, the ULN2003. Unipolar steppers can be driven by one of those (if the current on each coil does not exceed 500mA, if it does you can double the ULN2003s in parallel). The picture shows all the connections to the Arduino:

1) The yellow wire from the Arduino senses the voltage from the potentiometer and can be used to control the stepping rate. I don't think I need this. I might add a temperature sensor, though.

2) The purple wires from the Arduino control the four coils. They are connected to pins 1-4 of the ULN2003.

3) The black wire from the Arduino is Ground. It is connected to pin 8.

4) There's 5 wires from the stepper. We need to know which one is the Common and we need to connect it to the stepper power source (12V in my case). All the others must be connected to the output pins of the ULN2003 opposite pins 1-4, so pins 13-16. The Common should also be connected to pin 9, opposite pin 8 (Ground). The picture seems wrong on this count as all 5 stepper wires are connected to pins 12-16. The schematic, on the other hand, has it right, I think.

[martin_h]

If you use the ULN2803A octal darlington driver you can double up the outputs on one chip instead of using 2 seperate chips but stick a heatsink on cos it gets a bit warm

[ringz]

I've just downloaded the interface standards for ASCOM control of a focuser and for some reason I can't seem to get the compiled help file to work properly.

Has anyone GOT one that works.

EDIT: I'm now sorted. You have to go into the properties menu and allow the file to be used.

Martyn.

[ncjunk]

I know I had some problems with ASCOM but can't remember what they are...I think I lost the sample files at one point or couldn't install them properly in VB2008. It was just a case of trying to figure out where the files where meant to go.

Let me know how you get on Martyn.

Neil

[ringz]

Neil,

Did you ever post your code anywhere?

--

Martyn.

[ncjunk]

I posted some code in the yahoo group but it is not the latest.

I am missing uploading the updated software.. unfortunately I am in the UK until Sunday so won't be home until sunday evening..

I will check to see what I have posted online.

I think the version that is there would show you how things work (as a guide) but isn't the latest.

What do you need and can you wait till Sunday night?

Sorry I can't be more helpful

[John78]

You'd be better off not using obsolete stepper drivers really - and ones which handle microstepping etc... to take the load off the processor - if you end up with focus and tracking the arduino will start screwing up

Allegro | Product | A3977 Microstepping DMOS Driver with Translator

Much better just step and direction inputs needed and does microstepping for much higher resolution which is probably a bonus on the focuser.

Take a look at the reprap project for automation, temp controls etc... its from a different subject area but highly applicapple in the overall application...

Generation3Electronics < Main < Reprap

Stepper_Motor_Driver_2_3 < Main < Reprap

WebHome < Main < Reprap

[John78]

Actually even that 3977 is going EOL

Allegro | Product | A3980 Automotive DMOS Microstepping Driver with Translator

[ncjunk]

John,

Which driver is obsolete? are you talking about the L293? I hadn't heard anything but it would be nice to know if it is.

As for microstepping I wasn't planning on using it at the moment, I was more thinking of adding in a geared reduction. The Stepper I have will do 3 rotations to travel the full focus distance therefore I want to do a ration of 40:1 (around there).

The Arduino is working at the moment fine using the internal stepper function which we just provide step and direction BUT I need to test to see if any steps are being lost or the repeatability is a problem.

I don't think at the moment I need to worry about load on the processor just for focus control. The load will become a problem when I start wanting to add in Cloud detection and other functionality.

I reserve the right to change my mind on any of the above and deny I ever said it (learning from the missus...although she is normally right).

Neil C

[ncjunk]

In reality there won't be much code change between the internal Arduino Stepper function and using the chip mentioned for micro stepping if it was added into the software at a later date.