Grounds tied together?

[gottaluvlasers]

thanks everyone as always!

i have decided to just hook directly. No combining grounds together. im doing it the old fashioned way.
RED--->RED

BLACK---->BLACK

Pin 5 to R+ input on laser
pin 18 to R- input on laser.

and so on for each lase rmodule.

bottom line, this obviously wont hurt anything correct??

-Marc

[James Lehman]

bottom line, this obviously wont hurt anything correct??

-Marc

That's what volt meters are for!

James.

[DZ]

thanks everyone as always!

i have decided to just hook directly. No combining grounds together. im doing it the old fashioned way.
RED--->RED

BLACK---->BLACK

Pin 5 to R+ input on laser
pin 18 to R- input on laser.

and so on for each lase rmodule.

bottom line, this obviously wont hurt anything correct??

-Marc

That is currently the best way to connect it. But, I think its important to understand, that -R use to be the inverted side of +R. Whereas today, it is internally connected to pin 25 on the QM2K. In my projector, I still wire pin 25 to the -RGB color lines, which is a bit redundant, but I guess you never know when someone with an older board is going to plug into your projector and you suddenly find yourself with wierd color problems. I'm not sure when they made the change, but I would guess there are still alot of boards out there with differential for color. Interestingly, if you look at the pinout of the QM2K on Pangolin's website, it still shows the older differential output, however, if you look in the latest help file in your Pangolin folder on your computer, it shows that its at 0V potential.

[Pangolin]

Hi,

Actually, this is an excellent question. The absolute best way to connect the colors internal to a projector (as opposed to on the transmitting end -- at the computer) is to use true differential signaling inside the projector. This means that for red, you will be using both R+ and R-. (Same goes for the color colors.)

But here's the problem. First, you'll be lucky if you wind up with a laser that has analog modulation. I used to take these for granted. Then I borrowed a laser projector from a client... I also saw many lasers that had TTL modulation while in China.

Second, even if you do have a laser that has analog modulation as an input, and even if the connector does have two pins on it, only one of the pins really does anything meaningful. The other pin is connected to the ground on the power supply of the laser diode driver, and most often connected to the metal chassis of the laser, thus, laser diode drivers themselves are inherently single-ended.

So, it's kinda like whether you like it or not, if you tie pin 18 (red minus) to the laser diode driver, it gets connected to ground in an inadvertent way.

Now, this will cause a ground loop, just like it causes a ground loop if you connect ILDA pin 25 directly to the scanner amps. When you cause such a ground loop on the scanner, the result manifests itself visually, by producing "bent lines" in the scanned image. But for the color signals, it may not produce a result that is very noticeable.

The correct way to handle this (but a way in which I have only seen one projector do in my entire life) is to have differential receivers for the color, which accept the R+ and R- signals (and G+/G- and B+/B-), convert them into a single-ended signal, and then drive the laser diode driver from there.

Every laser diode driver that I have ever seen in my entire life has a single-ended modulation input. Theoretically, this is a no-no when it comes to use with the ILDA connector (on the projector side -- not the computer side, the rules are different there). So, ideally, you need a differential-to-single ended converter (simple op-amp and four resistors), so that all signals COMING INTO THE PROJECTOR are differential.

REMEMBER, the onus of differential communications is on the receiver, not the transmitter.

With all of this being said, yes, my description above is how you make a perfect projector. But lets get real here folks... this is a Laser Enthusiasts forum. Hooking the R-, G- and B- directly to pin 25 on the ILDA connector, inside the projector (or inadvertently connecting them to ground by virtue of the fact that you connect R- to the second pin on the laser diode driver, and then bolt the fricken laser to a nice metal chassis) is just what's done. And, at the end of the day, it *appears* to work fine. This is because there are far more problems with laser diodes and laser diode drivers, what with the differences in modulation characteristics between red, green and blue, and jelly-beaning that goes on, the difference between perfect connections and typical hobbyist connections will be simply unnoticeable...

Best regards,

William Benner