Re: [CAD_CAM_EDM_DRO] Parallel Port Woes

Hi Caudlet,

Nice posting! I've commented in the past on this. I found a "buffer
box" for the parallel port. Gives some isolation, and better signal
levels. PROBABLY also adds (as would yours) a little DELAY to the
pulses. As long as they don't get too narrow!

AND, at the time I was using a MaxNC driver, which doesn't have
opto-isolators! Never had any problems (with CNC hardware; don't ask me
about other hardware!).

Alan KM6VV


caudlet wrote:

>
> Having transitioned to using a Windows based controller program on my
> Engraving Machine and the parallel port instead of a proprietary
> driver card, I started to feel the need for more computer
> horsepower. I found a deal on a motherboard and chip (900Mhz AMD for
> 89.00) and added a few dollars for 128M more RAM. After the upgrade
> my machine just sit there never moving a step while the program
> cranked away. I chased all the wrong things like checking the
> cables, the grounds and the +5 power supply for the optoisolators.
> How hard could this be?! I finally disconnected it and moved the
> power supply with motor drive cards into the lab and applied the
> scope. The PC signal looked good enough but when I manually applied
> a ground to the step input with the PC cable disconnected I got a
> twitch from the motor...ah, a clue. Seems that the new PC's parallel
> port was a bit weak and could not sink the 30ma the driver cards
> needed. I searched through my goode box and fished out a 74HT07 open
> collector hex non-inverting driver chip. I ran the 6 step and
> direction lines though that little jewel and PRESTO, nice smooth
> moves. I could have used any open collector hex driver but the non-
> inverting one kept me from having to redefine all my output
> polarities.
>
> Lesson learned: New LSI printer port chips may not have enough pookey
> to drive a TTL load or an optoisolator input. If you are having funky
> things happening with the parallel port, maybe a buffer chip is in
> order!