telescope stepper driver?

[garymck (Gary)]

hi,
have just come across this telescope drve based on USB sound controllers. Looks good, but then I'm no electronics whiz. Has anybody here used it? Comments ideas etc?

Seems like a remarkably simple and inexpensive way to control and drive a scope?

http://soundstepper.sourceforge.net/#overvie

cheers
Gary

[bojan]

This is very interesting..
However, it seems to me this system still needs specialised audio circuitry (kind of analogue decoder to separate channels for RA and DEC from audio card stereo outputs, and audio card must have 3 outputs, so it is not standard with only L-R) with amplifiers (one stereo amplifier per motor), capable of driving stepper motors (couple of Watts for higher torque).. so this is not off the shelf product.
Also, those audio adapters and amplifiers must be DC-coupled (for very slow moving steppers, while guiding for example).

I am using one of those programs mentioned in a text as problematic CPU usage-wise (Bartels, it has to run in DOS mode), and it works great, despite the fact that it requires dedicated PC (cheap 100MHz pentium, running DOS).. However, if I find some time I may try and have a look at this, just for fun..

[garymck (Gary)]

Hi Bojan,

found a link to some more of the developers stuff:

http://www.astrofotos.info/index.php...p/Projetos-ATM

I also used to use a Bartels drive (Avandonk bought my Bartelized EQ6 years ago), unfortunately Mel has ceased supplying/supporting the old stepper system.

cheers
Gary

[bojan]

Hi Gary, thanks for this additional info..
$12 (ebay) for adapters is not much, but it the near future the support/availability may be gone (and Mel is still supporting his system on yahoo group, if it really needs any support at all). However, the required additional analogue circuitry may be a problem for many.
I am still wandering how this guy (Maciel) sorted out DC operation of steppers (and microstepping..). And, it seems no encoders are supported?
It's time to download the software and have a proper look at it

EDIT:
DC-operation is sorted out by using DC -coupled audio-adapters..
I tried the software on my desktop (with on-board audio adapter), it seems it works.. I can hear tones, as expected

This is definitely worth trying !!
Perhaps encoders will be supported via ASCOM platform?

EDIT2:
Power consumption/dissipation may be an issue (depends on how microstepping is done.. Class-d amplifier may be OK as it has internal PWM)

EDIT 3:
Conclusion - definitely worth trying.
However:
- No microstepping (bad... my EQ7 has 9arcsec/step resolution in full step mode, which is not good enough resolution for guiding. However, it might be quite OK for tracking as output seems to be sinusoidal)
- No direct encoder interface (must go via ASCOM, I hope..)
- Now I need to check the rest of functionality (and connectivity to other parts of the system - encoders via ASCOM, CdC or Stellarium... )
Otherwise.. OK.

[rally]

Pretty cheap solution ! $2 each for the USB Audio device

http://www.dealextreme.com/p/virtual...und-card-22475

Now he just needs to add in some encoder feedback and a home position and that would be a real winner.

[bojan]

Originally Posted by rally

Pretty cheap solution ! $2 each for the USB Audio device

Don't forget to add amplifiers to the total bill.
Then the cost becomes very similar to Bartel's stepper system (which does all you could ever need..).

[bojan]

Well, couple of those USB-Audio dongles from ebay are ordered ...
So, after looking into output waveforms, I will know more.

However, it seems that the dissipation of the proposed current driver design (car radio amplifier) will be definitely too high (resulting in high current consumption), especially for low-resistance motors, so chopper should be used instead (for example, NJM3771, this chip is capable of handling 700mA per coil, enough for high-torque motors). Of course, the proposed driver circuit must be modified accordingly.

[Ayatola (Marcelo)]

Hi Bojan and Gary.

I already used the Maciel's SoundStepper in our 16" Dob. The system works very well. Easy and cheap to assemble.

Now I'm working in a new approach to use the system. I'm building a EQ mount with harmonic gears and 5 phase stepper motors. To control this motors I bough a pair of specific drivers controlled by square pulses. To generate pulses and control the drivers I will use the SoundStepper.

16" dob base in action
http://www.youtube.com/watch?v=M-zQBYgdxMw

Some pictures of my small project.
http://www.astrofotos.info/index.php...Projeto-Clonus

[]´s
Marcelo

[bojan]

Hi Marcelo,
This is very interesting..
Are you going to obtain the special version of software (with square pulses)? Or you will simply shape them with Schmidt trigger and use harmonic reductor to achieve required resolution?
I would be interested in step-dir pulses from audio card (or anything else, for that matter..) - I already have drivers with Allegro chips (16microsteps), I am using them with my Bartel's system - but Maciel's approach may be more convenient because everything can run on single PC (instead of minimum two as it is with Bartel's scope.exe).

[Maciel (Maciel)]

Hi all,
Thanks Bojan for contact me by email.

The Soundstepper is pure software, it generates audio waveform only. Every circuit capable of convert these audio signals into stepper windings' current will work. Each stepper needs a separate USB audio device, L+R channels: each channel drives a winding.

I'm not electronic engineer, then I was not capable to design a full PWM circuit with current-feedback for use with Soundstepper. Instead, the analog design was quite obvious for me, and the dissipation / power consumption issues seems minor... The power consumption (current) is the same of stepper's total current, and the dissipated power is (supply voltage - winding voltage) * current. Much more than PWM devices, of course. But works great!

About some questions in this thread:

1- Soundstepper works with standard 2-channel audio devices (don't need 3-output audio cards). Up to 4 steppers, using a separate audio adapter for each.

2- No, Soundstepper don't support encoder feedback at all. Is on the roadmap, but not for this year. My priority now is finish the field de-rotator algorythm.

3- Class-D USB audio adapters (SJ-588) are treated as analog, the output waveform is low-pass-filtered.

4- Yes, Soundstepper does microstepping: 90 microsteps per step (much more than stepper's accuracy). You can check this with a laser pointer on a stepper axis (using Soundstepper's "static positioning test" option). Like these: http://www.astrofotos.info/index.php...-ATM/GoToLaser - These "poor man's direct drive mount" have less than 10 arc-minute accuracy over the entire sky, and less than 2 arc-minute for tracking an object over 1 hour, with no reduction, the steppers' axes are the mount axes! Use the "reduction calculator" at http://soundstepper.sourceforge.net/#steppersmounts - For visual use you can use reductions as low as 1.5 arc-minute per full step (like our 16" dob), and for astrophotography, 10 arc-seconds per full step is fine.

My audio analog circuits are SUGGESTED, and You're free to propose a new, better circuit. I'm very interested in Bojan's approach with NJM3771!

The basic guidelines for circuit design for Soundstepper is:
1- all DC coupled: at low speed it is very important.
2- stepper windings current feedback: the audio output level need be translated into current (no voltage), because the current (not voltage) generates torque. At high speed it is very important.

The "pulse/direction" version are now available for download at http://soundstepper.sourceforge.net (is an option in "test and adjust" window). With this option checked, the left channel is pulse (90usec width), and the right channel is direction. Depending on the output voltages of the audio devices, and drive inputs, the audio signal may need to be passed through low-pass filters and "schmidt triggers."

Thanks for the interest, and sorry for these long text in bad english.

[Ayatola (Marcelo)]

Hi Bojan.

Maciel was faster than me and answered their questions

I will use two 5 phase driver to control the motors. I hope that does not require any other electronic to control it but it only depends of the soundcard output voltage. The driver need a 4.5v pulse to work.

With this approach I expect get 250 microsteps (resolution of 0,0000576º or 0,207 arcsec with a 1/50 harmonic gear) and 2 selectable speeds.

Maciel already modified Soudstepper to use square pulses to control this drivers, now I need expend some time to perform a lot of tests.

I'm using this driver to this project:

http://www.orientalmotor.com/product..._operation.pdf

[]´s
Marcelo

[Poita (Peter)]

Looks like lots of fun. I used an audio signal to drive the stepper motor on my telecine rig a while back. I'll have to give this a go.

[bojan]

Hi Maciel,
This version (with step-dir pulses as output) is potentially absolute winner
Now I can use my driver modules (http://www.pololu.com/catalog/product/1182) with your system, and the interface circuit might be much simpler than before.
Looking forward to test..

EDIT:
I have suggestion: Could you try and use mic input of those USB audio adapters for encoder quadrature signals (DC coupled. of course..)?

[garymck (Gary)]

Ho Maciel,Bojan and Ayatola,

I'd love to build a drive using this approach, but am not electronically literate enough to follow the diagrams on soundsteppers page. I am able to build with a simple diagram to work with (managed to complete a Cookbook 245 ccd that worked) so is there anywhere I could find a really easy diagram of some electronics to build? A Dummies guide would be really helpful.

cheers
Gary,

[Maciel (Maciel)]

Bojan, Soundstepper with "pulse/direction" drive method is far easier to interface with automated stepper drives....

BUT this way it loose the microstep feature: while using analog drive method, the Soundstepper does 90 microstep per full step. Using pulse/direction drive method, the Soundstepper "step" is a single pulse. The microstepping is now a drive's responsibility, and have a microstepping drive (or a BIG reduction) becomes essential.

Is possible to design an analog-controlled PWM drive with current feedback?

Garymck, what do you mean with "simpler diagram"?

[bojan]

Originally Posted by Maciel

....Is possible to design an analog-controlled PWM drive with current feedback?
....

Hi Maciel,
It is possible, and I am working on this (the idea of using NJM3771 or similar driver is the answer )

Originally Posted by Maciel

....Using pulse/direction drive method, the Soundstepper "step" is a single pulse...

I am aware ot that. The Allegro chip that I am using as stepper driver provides 16 microsteps, and in a combination with 0.9° steppers gives me enough resolution for smooth tracking (0.23 arcsec/microstep)

[garymck (Gary)]

Originally Posted by Maciel

Garymck, what do you mean with "simpler diagram"?

Maciel,

I mean something that show a component layout on a a piece of stripboard like the diagrams on this page:

http://www.kpsec.freeuk.com/stripbd.htm

That way electronics dummies like me can simply put a component where it has to go rather than having to build a rats nest of wires . I'm sure the electronics parts are what stops lots of people from using your system. some of us need the equivalent of a "paint by numbers picture" .......

I've oreder 6 usb sound dongles hoping to follow someone elses lead....

cheers
Gary

[bojan]

Gary,
you have the links for what you need on Maciel's page, a bit lower from the middle of it :
http://soundstepper.sourceforge.net/...for_SJ588.html

[Poita (Peter)]

A PCB wouldn't be too hard to make from that diagram either.

[MrB (Simon)]

Originally Posted by bojan

The Allegro chip that I am using as stepper driver provides 16 microsteps

Hi Bojan,
Which chip are you using?
I have just ordered a couple of A4988's to experiment with.
What are your thoughts on the Allegro's? It seems some people have been having problems with missed steps at low speeds and low currents while microstepping at x8 and x16, tho apparently the A4988 handles these conditions better than others like the A3977/79's