[Color Computer] [coco] Learning MW C

[jdaggett at gate.net]

On 14 Aug 2006 at 11:11, Gene Heskett wrote:

> On Monday 14 August 2006 11:00, jdaggett at gate.net wrote:
> >On 14 Aug 2006 at 0:32, James Diffendaffer wrote:
> >> --- In ColorComputer at yahoogroups.com, "George's Coco Address"
> >>
> >> <yahoo at ...> wrote:
> >> >Should I wish to step these motors faster, I need to also use
> >> > a modified sine wave. I figure four bits per coil could do this. Of
> >>
> >> course,
> >>
> >> > this takes more time for the computer to do and speed is getting more
> >> > serious.
> >>
> >> Can you precalculate a table for the sine wave and then just figure
> >> the starting point in the table to start sending values from?
> >
> >*************************
> >
> >Analog Devices makes low frequency DDS (Direct Digital Synthesis) chips
> >that uses 32 bit serial or parallel command to set the frequency.  The
> >AD9831 will synthesize any frequency from ab out 1 Hz to 12.5 MHz in 1 Hz
> >steps. A well designed post filter and an external 25MHz clock frequency
> > and then the computer can just upload the frequency encoded in four
> > bytes to the chip.
> 
> Which is nice, but where then is the motor?  How many cycles has this chip 
> generated since the last time it was updated?  Its a question that in the 
> interests of not ruining the parts because the bit went too far, cannot be 
> ignored.
> 
> >james
> 
Gene 

I was offering an external hardware solution to an internal sine wave table and external DAC 
to generate a sinusiodal waveform. This solution would change frequency every time a new 
32 bit command is entered. With 32 bits in the phase accumalator and a 25MHz clock the 
frequency precision can be better than 0.01 Hz.  Chips like these can generate frequencies 
up to about 500MHz. Also the frequency generated is very clean and quite devoid of 
harmonics. 


DC motor (Servo) speeds can best be controlled by a PWM and controlling the duty cycle to 
obtain speeds. AC motors are a bit more complex. Stepper motors are rather easy intil you 
get into microstepping. 

james