[Noisebridge-discuss] Do we have a USB to Parallel (printer) port converter?

[Andy Isaacson]

On Tue, Jun 26, 2012 at 06:57:37PM -0700, Hao wrote:
> However, I don't think Arduino-parallel converter can be used in a
> situation that I need it to control MAXNC CNC machine in realtime, from
> EMC2/Axis software on my laptop. Can it?

You definitely cannot run MAXNC over a USB parallel port adapter.  As
Martin says, a PCI or PCIe or even ExpressCard or PC Card (PCMCIA) would
be more likely to work, whichever one your PC has.  Central Computer
definitely has PCI and PCIe.

The reason why MAXNC can't use a USB-to-parallel adapter is, you need to
send very precisely timed signals.  USB introduces jitter and latency,
since the USB parallel port adapter uses a whole USB packet to say "turn
off pin 12" and similar.  (If you're *lucky* it's one packet, more
likely it's doing a multi-round-trip conversation between your USB
driver and the chipset in the adapter.)

If you instead develop an Arduino adapter for the device, you can use
the Arduino to provide the precise timing that you need.  Then MAXNC
just says "hey arduino, pulse pin 1 500 times at 40 Hz, then pulse pin 2
30 times at 60 Hz".  The Arduino takes care of making sure the timing is
precise.  Since it's a microcontroller it's very good at flipping bits
at exactly the right millisecond.

I'm pretty sure there are Arduino libraries for this application
already; have you looked around at all?

-andy