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

[Brian Pitt <bfp-at-earthlink.net>]

the PC speaker can be reprogrammed to generate a PWM signal 
using the spindle enable pin on the paraport to gate the output from the
speaker to the spindle 

or using serial DACs 
paraport version (bit banging a crude serial port on the lpt port)
long URL
[
http://www.e-insite.net/ednmag/index.asp?layout=article&stt=000&articleid=CA170222&pubdate=10/11/2001
]
serial port (RS232) version
[
http://archives.e-insite.net/archives/ednmag/reg/1997/030397/05DI_03.htm
]

for the feedback signal a PIC to read the spindle encoder and
send position or velocity updates back on the serial port 
if the PIC has enough pins it could also be used to offload the 
analog/PWM function from the PC

there are some multifunction 'smart' servo amps that have all this built in
a good example would be this one (cause its the one I have :-) 
http://www.compumotor.com/manuals/BL/BLHX.pdf
the drive can be programmed to work in several modes for
positioning,velocity and pulse folowing with an electronic gear ratio
for threading/tapping
it communicates over the serial port with simple mnemonic commands and
includes some extra user I/O pins 

Brian