Laser blanking

[DPSS]

Hi Adam,

Sorry for the little disappearing act I've played for the last week or so but I've been changing telefone company and got mi Internet back just yesterday.

Thanks for explaining about the TTL, I'll be trying your idea with the diodes shortly.

Instead of posting images I've done a couple of videos of the Scanpro's in action so you can take a look at them. I hope the quality is good enough, I couldn't achieve anything better with my digital camera. If not let me know and I'll post a few fotos.

This one is without blanking:

http://www.youtube.com/watch?v=a1bAdt3cx_0

and this one with blanking conected on the green channel:

http://www.youtube.com/watch?v=0hmBWqrojn8

I haven't looked in to any info about tuning yet, so I don't even know what I'm looking for to distinguish if they're well tuned or not.

Domingo.

[buffo]

Hi Domingo;

Glad to hear you've got your Internet connection back! The videos look fine. Based on the one without any blanking, I'd say your scanners are tuned well enough for what you're doing. They might need a little tweaking here and there to be perfect, but I didn't notice any serious overshoot on any of the corners, and overall the images looked fine.

If you want to check the tuning, you're going to need to be able to load up a test pattern or two. I suspect that the DMX board you have does not have any test patterns pre-programmed, however. If that's the case, then you'll need to wait until you have a controller (DAC) before you can tune your scanners. But I don't think it's anything urgent... As I said above, your scanners look OK for now.

Hook up the diodes and then shoot another video of the unit in operation. Hopefully this time we'll see all the patterns without any of the retrace lines.

Adam

[DPSS]

You're right, there isn't any test patterns on the DMX board, but I should be recieving my correction amp kit soon so, once I put it together and hook it up to the USB soundcard, I'll hopefully be able to try one.

I'll let you know when I've hook up the diodes.

Thanks for checking the videos.

Domingo.

[heroic]

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.)

Funny you mention that, because all my analogue lasers seem to float to full power when disconnected.

I have a blu-ray diode on a Norm board which seems to do this, a CNI red, some off-brand green and a blue that appears to actually be a Laser-Wave- all of these seem to go to full output when nothing is connected to the mod input. It's quite handy actually because it makes it easier to set the galvos up using a signal generator :-)

[buffo]

That's quite interesting! I've never heard of an analog laser going to full power like that with nothing connected to the modulation lead.

The only CNI laser I've experimented with was a TTL unit (which did float high when unconnected). I've never messed with any of the laserwave units. Still, I've spoken with others that have owned both CNI and Laserwave units, and their experience matches mine - namely that the modulation line on a TTL laser will float high on no input, but the modulation line on an analog laser will not.

Hmmm... Evidently it's more of a "guideline" than a hard and fast rule!

Adam

[djscsi]

That's weird. Analogue driver should be expecting 0-5V modulation input, so should produce no output with 0V on the modulation input. However, there is usually an "Idle" adjustment (potentiometer) as well as the "Main" adjustment so its possible that the idle current is set too high?

I have a FlexMod2 driver as well as some homemade ones (Stan_Ham driver) and they produce no output when there is nothing connected to the modulation input. I think TTL drivers have the modulation input tied high (pull-up resistor) so the laser is on with nothing connected to the input.

The suggestion about tying all 3 output channels to your laser input using 3 diodes should work for what you want to do, though.

[heroic]

That's weird. Analogue driver should be expecting 0-5V modulation input, so should produce no output with 0V on the modulation input. However, there is usually an "Idle" adjustment (potentiometer) as well as the "Main" adjustment so its possible that the idle current is set too high?

My analogue lasers go out if you drive the input to 0v, or if you short the input.

I've also seen some that have antisense inputs, so they produce maximum output at 0v, and nothing at 5v; not sure why this is considered desirable, but there you are.

[DPSS]

Well, I finally managed to find the time for buying the diodes. My electronics knowledge is quite limited and rusty though, so, just to make sure I won't burn out something, is this the correct way to set them up?:



Thanks.

[mixedgas]

[quote=DPSS;87060]Well, I finally managed to find the time for buying the diodes. My electronics knowledge is quite limited and rusty though, so, just to make sure I won't burn out something, is this the correct way to set them up?:




YES!

If you have "Heroic's Malady" and your inputs dont pull down, we'll add a part.

Steve

[DPSS]

Thanks Steve,

I'm affraid living in Spain all my life and not speaking english very often and with family most of the time has limited my knowledge of the language in sone ways so, at the risk of sounding quite dumb, I have to say I don't have a clue what you mean when you say:

If you have "Heroic's Malady" and your inputs dont pull down, we'll add a part.

Man, I feel stupid.