Re: The mechanical part of my router is done!

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Charles Knight <charles@i...>
wrote:

> OK, guys...I need a little bit of help. Who's good with

electronics?

>
>

Chuck: Harvey saved me a lot of typing. Make the mods he lists and
you will have an opto isolated driver card. Make sure the logic
outputs on the parallel port pins are active low. Parallel ports
sink current to ground better than they source current. Using the
resistors shown (R1;R2) the port will have to sink almost 20ma per
pin. That may be asking a lot from a motherboard P-Pot. You want
things to happen on the low going pulse from the computer. Set your
software to output active low signals.

One of the things that has me scratching my head about the circuit is
that pin 18 on the 297 does not show to have a pull-up to the on-
board logic supply. I would think that this pin needs a 10K just
like 17 unless it internally has a pull-up. It needs to swing
between the on-board VSS +5 and the circuit ground presented when OCA
is turned on after your mods.

Let us know how it works out.