Two Lasers off One DAC

[JimBo]

I want to run 2 of my lasers together.
I have my RGB which is in the centre of my display and two RG projectors one at each end.
I only want to do beamshows on the RG projectors with the X invertered on one of them so the beams join in the centre.
What ways can I connect them up?
Can I run both RG's off the same DAC, can I run 2 seperate DACs off 1 parallel port or do I have to keep them both totally seperate?

Jim

[yaddatrance]

Most scanheads themselves are "noisy" and would cause a bit of noise on each other.

I would build a circuit using one TL074 configured as 3 unity gain and one inverting opamp
and drive the scanners off that. Let me know if that sentance was gibberish and you'd
prefer a simple schematic.

[JimBo]

A schematic would be great.
What I was thinking of doing if I was to use just 1 DAC would be adapt the popelscan design to uses just one set of the D/A converters but parallel up another set of the 74's and pots for a little bit of isolation.

Jim

[dave]

We have never had any issues daisy chaning projectors together off the one ilda cable.

Dave

[yaddatrance]

That would work where the systems were on common grounds or did not use pin 25 (or a shared bus for color modulation)... The safety of daisy chaining would depend 90% of projector design and 10% on whether the building was sanely wired. (those statistics came out of my bum)

The problem is that many of the bigger venues which are the ones most likely to require several projectors are the ones most likely to have sketchy power problems.



The quick circuit above is what I recommend, on the left is just a bunch of unity gain voltage followers, which is the safe way of ganging projectors together. You can use TL074, TL084
or NTE859 quad JFET opamps which run about a dollar in small quantities can be bought at Fry's....

This circuit works for both single ended and differential systems. And you will probably want to use it on the color channels too.

If you want to make the X axis inverted, Change the top opamp (X+) for the one on the right.

You can make the circuit more noise tolerant by adding 100 ohm balancing resistors on output of the opamp, and using one circuit per projector you're wiring in. But it shouldn't matter too
much. You can even wire this deadbug fashion and heatshrink it inline a cable.