Re: [CAD_CAM_EDM_DRO] Parallel Port to Power Supply Grounding Differential

In a message dated 7/8/2003 12:09:49 AM Central Standard Time,
elson@... writes:

> If you have the Gecko drives that can only work with a negative common
> terminal, then that common should be connected to the parallel port's ground.
> You will likely need pull-up resistors from the step and direction signals to a
>
> +5 V derived from the computer as above.
>

If your parallel port has "old TTL output-chips", not newer 74HCnnn types,
you may have difficulty "powering" the opto-inputs to the Gecko drives, as these
draw 16 mA (nevermind the paperwork! I measured the actual current into each
of FOUR such inputs on recent G210's, connected "Neg. Common", and they EACH
drew 16 mA!) Using "pull-up resistors" will "partially illuminate" the IR
LED's in the opto-isolators, and expecting the "TTL high" outputs to pull those
inputs sufficient/reliably to sufficient + level to "fire" the LED's properly
will be, well, "poorly defined".

What I have found works well is to use a 74HCT541 octal non-inverting buffer
on the 8 data-lines of the PP. This will give you "guaranteed" 25 mA per
line, with a min. output voltage of 4-4.5 volts! I know, I MEASURE things, once
working! That buffer IC is NOT an "opto-isolator", but it DOES further
separate things, and won't cost much at all! Long live 'HC ! ! ! Jan Rowland



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