Have you ever heard USB speakers stutter?

Think what might happen to your hardware if a USB driven servo/stepper
'stuttered'.

I think you need to have enough autonomous intelligence to handle the
inevitable 'misses' from the PC end, especially when running any flavor of
Windoze.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

----- Original Message -----
From: Lawrence Glaister <lg@JFM.BC.CA>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, December 19, 2000 10:25 PM
Subject: [EE]: USB stepper drive system


> There has been a lot of talk lately on the list promoting the development
of
> some "smart hardware" to supplement the  PC's poor performance. The second
> item that is rearing its ugly head is that pc's are rapidly losing their
ISA
> slots and their serial/parallel ports. I also subscribe to the usb-devel
> list and am getting a pretty good feel for what usb is capable of. I use
EMC
> as the PC end smarts. It basically works well as an open source gcode
> interpreter that expects to output a drive signal and receive back an
> encoder signal for each axis every 1ms or so (programmable). The usb bus
can
> be thought of as a fast 12mb/sec serial port (about 1/2 of this is
actually
> usable). I am starting to think along the lines of a usb board that
contains
> some number of rate generators (like Marriss's DDS system or even pic
based
> software DDS) to generate the stepper drive signals smoothly and the same
> number of encoder interfaces (either in hardware counters or possibly pic
> based software interfaces). The interface would use an isosyncronous read
> port and a write port to read/write the command/status signals every ms. A
> four channel card would cover most applications although once design is a
> little further along, it may be possible to put 6 axis on a card and
produce
> them in various states of population. USB support is getting pretty good
> under linux, with quite a few example drivers. Between the lists, there is
a
> lot of talent available... where to we need to be in a year from now?
Would
> USB make sense in a shop environment for getting machine control
information
> in/out of the computer?
> Would DAC outputs for servos make sense? Would +-50ma outputs make sense
for
> driving hydraulic servo valves? How much would the board cost to produce?
It
> is going to be hard to beat the cost of an add-in parallel port. The card
> would definitely make laptops or low end Macs like an iMac attractive as a
> dedicated controller. Just some ideas to think about for the next
generation
> cnc controllers.
> =======================================================
> Lawrence Glaister VE7IT             email: lg@jfm.bc.ca
> 1462 Madrona Drive                     http://jfm.bc.ca
> Nanoose Bay BC Canada
> V9P 9C9
> =======================================================
>
> --
> http://www.piclist.com hint: The list server can filter out subtopics
> (like ads or off topics) for you. See http://www.piclist.com/#topics
>
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.