Earthing Norms DAC...

[rog8811]

I had a good look at what I had connected up and found my error.

I had used 3 pin molex headers with one pin cut off to fit in the DAC board. One was cut left hand, the other right hand....I then did my plugs both left hand...After moving the pins around X & Y are now working. With no blanking wired in yet it is hard to set up so that is my next job.

Regards rog8811

[tocket]

Hehe, easy mistake to do. I guess that's why it's good to have color coded cables with the correct amount of connectors. It just sucks that you always realize this after having already soldered the damn thing.

Do you have a laser that supports blanking? If you do it's an easy thing to do. I ended modifying a green laser pointer (mutilated it with a dremel to extract the diode and optics) to run it from a die4drive. Modulation doesn't work that great though; seems the laser turns on too early (???, would have expected the opposite), before the scanner is in position. Would be interesting to see if you have the same problem.

[carmangary]

Modulation doesn't work that great though; seems the laser turns on too early (???, would have expected the opposite), before the scanner is in position.

That's normal. If you tell a diode to turn on at the same time you tell a galvo to go to point X,Y, the diode will almost always win and you'll see a little bit of light leading up to point X,Y.

[tocket]

It's more than just a little light though, especially at high scanspeeds. If I add some blanking points to the beginning of a path the problem is solved, but I don't really feel like doing that to every frame in every ILD-file I have.

Oh well, I just order the FB3 eval kit... see if that improves things.

[rog8811]

I have had awful trouble posting tonight, I created this one in word so that I don’t lose it for a third time……

I have a drive board with blanking for red and green, it is the DX 70mw red driver, which has a socket for a green with blanking as well. I have been told that 0.3v =off and 0.2v = on, I would have guessed that TTL would be 5v, what do I need to do…use a resistor across the blanking output to match the voltages or something?

My 2 blue rays are running from a home made driver and I was thinking of trying an opto-isolator for pseudo-blanking, unless someone has a better idea?

I ran all three lasers for the first time tonight…the rig was roughly aligned but I was pleased with the result, to the eye it is a good white though the camera picked out the misalignment….

Regards rog8811

[tocket]

I have a drive board with blanking for red and green, it is the DX 70mw red driver, which has a socket for a green with blanking as well. I have been told that 0.3v =off and 0.2v = on, I would have guessed that TTL would be 5v, what do I need to do…use a resistor across the blanking output to match the voltages or something?

Huh? Those are some weird signal levels. For TTL 2-5V is high (on) and 0-0.8V is low (off). Yours are kind of inverted, are you sure they're correct? I would make sure of that before designing a circuit. If you just drop the voltage you will have a laser that is on only when the DAC tells it to blank.

It isn't that hard to design such a circuit though. I made one by mistake (I wanted the circuit to do the exact opposite of what it actually did ). You basically use a variable voltage regulatur like the LM317 or 350 to supply the high (0.3V) as its maximum output voltage. Then you connect the TTL signal to the base of a transistor that switches on another route between ADJ and GND, effectively lowering the output. However the minimum output voltage of these is 1.25V, so you'll need to use a zener diode to drop the output voltage to your desired level. The tricky part here is choosing the correct values for the resistors. The schematic is basically the same as "5V logic regulator with electronic shutdown" in the National LM117 datasheet, but with different values on the resistors and a zener diode in series with the output.

You could probably design a better circuit using op-amps, but I'm not as familiar with those.

My 2 blue rays are running from a home made driver and I was thinking of trying an opto-isolator for pseudo-blanking, unless someone has a better idea?

What's the deal with you and all these weird drivers? If you have the schematic for the driver I (or someone else here) can probably come up with something to blank it.

[rog8811]

If you have the schematic for the driver

It is a basic, dual channel constant current LM317 setup, see drawing below of one half.

You basically use a variable voltage regulatur like the LM317 or 350 to supply the high (0.3V) as its maximum output voltage. Then you connect the TTL signal to the base of a transistor that switches on another route between ADJ and GND, effectively lowering the output

I have plenty of lm317's knocking around, could you do me a circuit diagram please. I follow drawings better than instructions

Regards rog8811

[tocket]

I need a program for that. Anyone know of a good free CAD/whatever program for drawing circuits?

Otherwise I'll draw it by hand and take a picture of it.

[rog8811]

I use mgi photosuite but you could do it in paint

Regards rog8811

[tocket]

Ok, now I have a schematic for that weird DX driver... see the attached file.

You'll have to work out what values to use for R2, R3 and the zener diode as I'm too tired to do that now (1 am here). If you get stuck I'll help you with it tomorrow.

The output voltage is given by:

TTL low:
Vout = 1.25V*(1+R2/R1) + Iadj*R2 - Vb

TTL high:
Vout = 1.25V*(1+(R2*R3/(R2+R3))/R1) + Iadj*R2*R3/(R2+R3) - Vb

Where Vb is the breakdown voltage of the zener diode.

I've never used zener diodes before, but apart from that I know the circuit works. I think it should work now as well. I'm a chemical engineer though, not electronic.