Re: How to get a signal to controll spindle speed?

[John Sheahan <jrsheahan-at-optushome.com.au>]

Hi Ray

On Sun, May 19, 2002 at 04:41:52PM -0400, Ray Henry wrote:
> 
> I should try some USB with the BDI-TNG and see how it does.  If it is any 
> good, we should hack EMC to create USB out that is compatable with Steve 
> Stallings USB motion control board and see how it goes.  From there we would 
> have a better idea of what is possible here.

I'll need to have a look at Steve's board, don't know it.
I need to build some USB peripherals over the next few months, time I 
learned somethign about it.

> 
> > A more reasonable solution would be to stuff a small
> > opto interruptor or hall effect onto the shaft, connect that
> > to a single chip PIC,  and get serial speed messages from that.
> > Serial could then go into  standard serial ports, or usb serial,
> > or a multiport serial card
> > for the wealthy ones. usb devices on cypress stuff is pretty
> > easy to add.
> > I can post code and circuits, even a couple of proto boards and
> > programmers  for the PIC if people are interested.
> 
> This is great.  Anything that you want to put up could go in the 
> LinuxCNC.org/dropbox.  If you wish we could put a PIC page up on the site and 
> give you control of it.

Happy to do that, but not for the next 3 weeks. I have to get out a
few different PIC things for work reasons. Some of them could be
relevant here, I'll post when done.  
I currently use simple PIC boards I have done for home control stuff, 
temperature, rainfall, some doorlocks, and remote NMEA instruments.
They would need a tweak to get RPM. but can handle pulse counting as
is. 

> 
> > What kind of feedback comes from the laser as to power?
> > And I thought the thread started with a PWM request. where did analog
> > come in? must have missed something key.
> 
> I don't think that you missed anything.  I think that I took a leap from the 
> spindle speed signals used to control laser power that was the initial post 
> to a feedback system that might lead us to a low cost closed loop spindle 
> control for stepper driven mills.  And the leap I took was toward both 
> velocity and position.
> 
> To get us back onto Jacob's track, the PIC you suggest could use the existing 
> second parport spindle signals.  These are spindle forward, reverse, speed 
> up, speed down, and brake.  Off and on are easy for me to understand.  Up 
> down is also rather easy but without feedback, how would you know where the 
> power setting was on the ramp.
> 

ok, I see the issue.  
Most positioning stuff is relative to 
the start (home) position. 
stop, then  start the object and provide 4 up pulses should get you 
to a known spot??   Feedback would obviously be better.

> Ray
>