DAC - DMX switch

[rog8811]

My new projct is well under way (RGB graphics scanner) but I have a question for the computer experts here.....

To connect the supplied DMX or the DAC I will need to have an 8 pole switch (See Drawing)

I could just use a printer switch box, with a mechanical switch....that though is a bit low tech.
What I want to do is to use a belkin auto printer switch (see photo) this allows 2 computers to use one printer....or for my use to allow the X & Y drives and laser blanking to be switched from 2 sources.

The question is, can this switch be configured to do this job? I am not sure how it selects which input to pass to the output, can it be done by setting a line on the parallel port on the computer hi/lo????

Regards rog8811

 

[rog8811]

I would change the title to "naked dancing girls" to catch the eye...... but then TL would delete it for not correctly descibing the thread

At least it would get more people looking at the thread though...and someone may know the answer to my question :-[

Regards rog8811

 

[ajohnson]

Well, it *might* be possible.  If you do a google search for "Interfacting to the IBM-PC Parallel Printer Port" you will find some good info on what pins do what, and why.  Using the data lines for what you want to switch might do the job.

HOWEVER

There's a potentially big problem here.  The parallel port lines are meant to be TTL signals of either 0v or +5v.  If you run your galvo signals (analog -5v to +5v) thru the box, a few things could happen:

1) It might actually work (yay!) OR

2) If the box applies any kind of IC/chip-based logic to the signals, you could lose the portion of the galvo signal from -5v to 0v.  They'd flatline at GND (0v).  OR

3) Not only would #2 happen, but the positive portion of the galvo signal would be changed to TTL and be either 0v or +5v, thus losing everything in between.  OR

4) The unexpected signals you send cause the magic blue smoke that makes the switchbox work to exit said box, transmorgifying it into a small white paperweight.

My money is on #3 or #4.

If you insist on hooking up both things at once, I'd suggest you either go for a low-tech switchbox (that might introduce some noise though) or look for a different solid-state box that can definatly handle signals of -5v thru +5v.

Just my .02

 

[rog8811]

4) The unexpected signals you send cause the magic blue smoke that makes the switchbox work to exit said box, transmorgifying it into a small white paperweight.

Thanks for the response, I had, since posting, done a lot of searching. The TTL for the LD's looks eminently possible. As you say the stumbling block will be the +/- 15V for the galvo drives.

I picked up a switch from ebay, it arrived today, I will open it up to see if there is any way I can get it to work. Otherwise I have a plan B using relays.

Thanks for the input.

Regards rog8811