Laser blanking

[DPSS]

Hi everyone,

A few days ago, after setting up my Scanpro20's with my aixiz laser and connecting the blanking signal from the DMX board to the laser driver board, I realized some parts I should be seeing of the patterns and words being displayed without the blanking conected were missing.
Would this most probably be caused by the laser diode, its driver board, or the blanking signal being sent by the DMX board?
Thanks

Domingo.

[Diachi]

HAve you got the signal connected the correct way round ? ie. positive to positive negative to negative ?

-Adam

[DPSS]

Unless the cables are mounted the wrong way round on to the plastic connectors at both ends, they're connected correctly, because they can't be inserted the wrong way. I'm not at home right now, but I'll check this afternoon when I get back.
I don't think that's the problem though because I can see many of the patterns correctly, there's just some of them that are missing a piece or have parts that appear dimer.

Domingo.

[Insanity]

If you are connecting a green laser to the green input channel, pins 6 & 19 on the ILDA Standard DB25 connector and then playing a coloured frame, you will only see the green bits of the frame. The red and blue bits will go to the red and blue channels.

If your laser is connected to the Intensity pins 3 & 16 then all colours will be directed to the laser and you will see the full image irrespective of colours in the frame..

If you are using a QM2000 DAC you can go to the pallette setup and tell the software which pins you are connected to..

Not so sure about the DMX connections though, but I am guessing it must be a similar setup...

Mark

[DPSS]

Hi Mark,

I'm not using a DAC (haven't got one, yet ) or the ILDA conectors, just one of the 3 mod outputs on the DMX board. I've tried connecting the laser to the other two and it does seem to make a difference on some patterns so maybe you're right and I'm just seeing one of the three colours.
I was told by keeperx that buffo is the expert on the Scanpro's so I'll check with him to see if he knows something about this.
Thanks.

Domingo.

[Insanity]

Yes buffo will more than likely be able to help you, he is a fountain on knowledge ... Failing that I'm sure Dave at Laser Show Parts will know...

Good luck with that one, I'm afraid I don't know too much about DMX lasers.. I have a DMX board for my gratings, but everything else is controlled through the DB25's...

Mark

[p1t8ull]

he is a fountain on knowledge

Is "knowledge" some kind recreational drug Adams now hooked on then?

[buffo]

Is "knowledge" some kind recreational drug Adam's now hooked on then?

Yeah man... When I take a hit of this knowledge stuff, I totally feel like a fountain and shit... It's like, grooooovy man. And stuff. Totally!

In all seriousness though, I think Mark nailed it. Missing parts of a pattern isn't a sign of scanner trouble, but rather a modulation issue. I think Domingo needs to connect his green laser to the intensity signal rather than just the green output.

Unfortunately, since he's only using the DMX pattern board that comes with the ScanPro 20's, I don't think that's an option. (I'm not very familiar with those DMX boards, but I seem to recall that they don't have an intensity output.)

Nevertheless, here's an easy way to prove that the modulation is the issue: Disconnect the modulation line on the laser and connect it to the +5 volt lead on the driver. This should make the laser come on at full power and stay on. Now run one of the patterns on the DMX pattern board. You should see the entire pattern *and* the retrace lines where the scanners are moving to new positions and the laser would normally be off. The image will probably look very messy, but you'll be able to see if it's all there or not. If you can see the whole pattern this way, then you know your problem is that you need the intensity signal.

A possible solution (assuming that there isn't an intensity output on the board) would be to put a schottky diode in series on each modulation line (R,G,B) and then connect all three leads together and run that to the modulation input for your green. You'd loose some forward voltage across the diodes, but it might not be enough to make a difference, especially if the laser only supports TTL modulation.

Domingo: Couple questions...

First - does your green laser have TTL or analog modulation? (If it's TTL, you won't need to use a schottky diode. Any old diode will work.)

Second - can you post a picture of the problem you're experiencing, just in case we're not understanding what you're explaining to us? (A snapshot of the ILDA test pattern would be helpful too.)

Adam

[DPSS]

Hi Adam,

You're right, the DMX board doesn't have an intensity output.
It doesn't really matter though, I'd already seen the full patterns, including retrace lines, when I tried the scanners without connecting the mod output to the laser, because it stays on continiously at full power. It was seeing that the patterns were missing pieces after conecting the modulation, that made me worry about the laser blanking correctly in the first place.
Alhough I have to say my initial worry was that the quality of the laser diode or driver could cause the problem. The thing is I remember reading somewere about bad quality lasers not being able to blank correctly, this being caused by the inability of the laser to turn on and off fast enough.

Anyway, I'm not to bothered about seeing the full patterns from the DMX board, because I'll be putting together a soundcard DAC soon so I can create my own shows and, after all you've explained to me, I tend to agree it does look like the cause is related to using just one of the three mod outputs. The truth is I never thought the patterns stored on the DMX board would be mixing different colours.

About the type of modulation, the Ebay seller I bought it from said on the auction it's TTL, but I don't really know how to confirm it.

Well It's getting a bit too late for me and I have to get up for work soon so I'll leave the picture posting for tomorrow. You seem to have understood the problem perfectly though and, for the moment, I have no way of displaying the ILDA test pattern.
Thanks and good night.

Domingo.

[buffo]

No problem Domingo... I only wanted to see the test pattern to see if your scanners needed tuning. But that can wait for another time!

If your laser comes on at full power when there's nothing connected to the modulation input, it's almost certainly TTL. (Analog modulated lasers have to have their modulation line driven to 5 volts to come on at full power, but the blanking line on a TTL unit will usually "float" high when disconnected.)

Since it's a TTL unit, it will probably turn on at anything above 2.5 volts on the modulation input. So my suggestion of using standard diodes (instead of the more expensive schottky diodes) will work just fine. Pick up any 3 diodes (go to Radio Shack, even), and put them in line on each of the red, green, and blue modulation outputs from the DMX board. Then tie them all together (after the diodes) and connect that to your modulation input on the laser. You'll be able to see the entire pattern and the re-trace lines will still be dark, as they should be.

Adam