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.
