Grounds tied together?

I asked Adam this last night, and I just want to make sure I understood correctly...

Off of the DB25 connector, I have the Color lines wired off of the standard ILDA pin out configurations.
R+ pin 5
R- pin 18

G+ pin 6
G- pin19

B+ pin 7
B- pin 20

My question is....

i know a lot of you wired all of your - color lines together. (R-, G-, and B-) tied together and then wired directly to ILDA pin 25 (GRND).

Is it OK and the exact same result if i wired DIRECTLY to each color line. in other words-
pin 5 wired directly to positive input on driver for red laser.
pin 18 wired directly to - input on red laser.

Pin 6 wired DIRECTLY to + input on green laser. Pin 19 wired DIRECTLY to - input on green laser.

and so on with the blue laser.

Pretty much just avoiding tying signals together and wiring directly.

Is this ok?? Im assuming that the answer is yes. and this whole thing is prob just a dumb question. i just want to be sure. :)

Does one way have a benefit over the other way?

-Marc

Negative is NOT ground!

In a balanced signal line there are three conductors, +signal, -signal and ground. I have never seen a color modulation device that actually takes a balanced signal input, but I understand they do exist. What you really want (I think) is just the positive signal and the ground. And, yes, the ground is the same for all of them.

James. :)

Hi all

I have my modulation on my lasers connected to

R+ pin 5
R- pin 18

G+ pin 6
G- pin19

B+ pin 7
B- pin 20

no problems, my Gr and Blu are CNI and Red is Lasever, and as as the modulation is not referenced to Ground all it looks for is a 0 to 5v input which you will get accross the differental
output fro the Dac ( +/- 2.5v ).... if your laser modulation input is ref to ground then you will need to connect pin 25 to 18, 19,20 you should still get the full swing 0 to 5v from pins 5,6,7,

this works with mamba and with qm2000 Dacs but you will need to check your Dacs design before shorting to ground

all the best .... Karl

Quote:

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Originally Posted by Banthai

Hi all

I have my modulation on my lasers connected to

R+ pin 5
R- pin 18

G+ pin 6
G- pin19

B+ pin 7
B- pin 20

no problems, my Gr and Blu are CNI and Red is Lasever, and as as the modulation is not referenced to Ground all it looks for is a 0 to 5v input which you will get accross the differental
output fro the Dac ( +/- 2.5v ).... if your laser modulation input is ref to ground then you will need to connect pin 25 to 18, 19,20 you should still get the full swing 0 to 5v from pins 5,6,7,

this works with mamba and with qm2000 Dacs but you will need to check your Dacs design before shorting to ground

all the best .... Karl

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Have you ever tried leaving 18, 19, 20 out of it and just using 5, 6, 7 & 25?

James. :)

Quote:

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R+ pin 5
R- pin 18

G+ pin 6
G- pin19

B+ pin 7
B- pin 20

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This is perfectly fine for the QM2K since, internally, the -r, -g and -b are all tied to ground. Use to be that they were truely differential outputs, but I think because of many folks mis-wiring the thing, and almost no laser supporting differential input, they just made the color modulation outputs single ended, with the -R, -G and -B actually being ground.

X and Y are another story, these are truely differential outputs, if you have a single ended scanner amp, then you would want to tie -X and -Y to ground.

There is an excellent "hardware specific" answer! That should tell you something! ;)

James. :)

I found out the hard way because at first I used only pins 5, 6, 7 and a common ground. That worked with my Moncha DAC because it 18, 19, and 20 were tied to ground and 5,6,7 varied between 0 and 5. But then I hooked it up to an EasyLase DAC and my lasers didn't come on like they should. So, I went to using 5,6,7 and 18,19,20 and it worked and now I am happy with both DACs.

Quote:

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Originally Posted by carmangary

So, I went to using 5,6,7 and 18,19,20 and it worked and now I am happy with both DACs.

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How are your cables made? Do you hook 18, 19, 20 to the shield? Are they all independent?

I guess I could see a _pair_ of wires inside a shield with (5, 18), (6, 19), (7, 20) in the wires and 25 to the shield, left unconnected on the color mod input end. But what's the point? It's freaking single ended!

James. :)

[QUOTE=gottaluvlasers;52609]I asked Adam this last night, and I just want to make sure I understood correctly...

James, older QM2000 have a "gyrator" circuit on x and y, if you hook it to a differntial amp, its differntial, if you ground the minus side of the diff pair, it doubles the voltage on the plus side to feed -5<>0<>+5 to a single ended scanner amp. At least the first gen quadmod 2000 did that. color channels do not gyrate. At least thats how it was in St Louis last month and at LaserRave (tm) last year.

Steve

Quote:

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Originally Posted by James Lehman

How are your cables made? Do you hook 18, 19, 20 to the shield? Are they all independent?

I guess I could see a _pair_ of wires inside a shield with (5, 18), (6, 19), (7, 20) in the wires and 25 to the shield, left unconnected on the color mod input end. But what's the point? It's freaking single ended!

James. :)

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Can't remember if I have a shield or not. But the point is that 5,6,7 to 25 on the EasyLase is not 0-5v. The negative (or ground) wires to the laser modulation must be connected to 18, 19, 20 in order to get the full modulation potential. Maybe 18,19,20 are all tied together in the DAC but they obviously aren't at the same potential as 25.

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

Quote:

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Originally Posted by gottaluvlasers

bottom line, this obviously wont hurt anything correct??

-Marc

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That's what volt meters are for!

James. :)

Quote:

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Originally Posted by 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

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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.

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