Lot of Wiring Questions

[f22warzone]

Ok with some searching on this forum I was lead to this sight
http://www.laserist.org/laserist2008...onnections.htm
and in the Website there was this

"
The discussion about color signals above, as well as the diagram makes the assumption that the laser diode driver has differential inputs to begin with. As two examples, laser diode drivers made by Laserwave and by Viasho do have differential inputs, but, as two other examples, laser diode drivers made by CNI and Melles Griot do not.
"

Specs on what I Have
FB3 XE
ScanPro40's
I have a CNI laser with 30Khz TTL modulation
MGL-H-532/1200mW
The power supply is here
http://www.cnilaser.com/PDF/PSU-H-FDA.pdf
Laser here
http://www.cnilaser.com/PDF/MGL-H-532.pdf

And I am wondering if this will work with the color signals ( + & - ) from the FB3
They say nothing about it being differential
http://www.cnilaser.com/TTL%20or%20a...modulation.htm

Also I noticed on my power supply it has an interlock with forced reset and everything so it would make compliance really ease without other electronics. I was wondering if this interlock could be connected to the interlock from db 25 pins 4 and 17....

So does the FB3 produce voltage on these pins or is it mainly just a link thing and you supply your own voltage and way to check it?..... Also if you were to pull the usb from the fb3 by accident would the laser shut down, as would it falsely create a disconnection from the idla connector because it has no power to it?

Also if my laser gets power from the power supply through its special cable then I wouldn't be able to make the lasers ground go to my central grounding point because I would have to cut the cable right?
I am understanding that I need to keep my central grounding point separate from the case earth ground so I am guessing some type of block suspending above the case even though all it will have is pin 25 and the scanner grounds plus the shutter ground when I find one.
Thank you for all your help ..... to bad the only parts i have right now are the scanners and the fb3..... almost tempted to hook them up and try to do a laser show with my pen laser :P wouldn't have blanking but it would still work right? or would something blow?

[buffo]

laser diode drivers made by Laserwave and by Viasho do have differential inputs

That information may be incorrect. We have several LaserWave and Viasho owners here on PL. I don't recall any of them reporting that their lasers have differential inputs for modulation. I believe they all support single-ended (zero to +5 volt) input.

Furthermore, the FB3 XE does not have differential color output. The differential board (which was added to the XE model - it didn't come with the original FB3) only gives you differential output for X and Y. The color signals remain single-ended. (That is, zero to +5 volts.)

Also I noticed on my power supply it has an interlock with forced reset and everything so it would make compliance really ease without other electronics. I was wondering if this interlock could be connected to the interlock from db 25 pins 4 and 17....

Which power supply are we talking about here? The one for the laser, or another one? Need more information about this interlock on the power supply too. How does it work? (Break the circuit and it shuts down? How does it reset?)

So does the FB3 produce voltage on these pins or is it mainly just a link thing and you supply your own voltage and way to check it?.

No. The FB3 does not put any voltage on those pins. The ILDA standard states that the interlock pins on any controller are supposed to be connected internally whenever the controller is powered up. The controller does not apply any voltage to the pins, it just completes the loop between them. The projector is supposed to send a low voltage, low current signal down the cable and back via the two interlock pins. If the cable becomes disconnected at either end, this will break the loop, triggering the interlock. All the interlock logic needs to be inside the projector. (Well, some people put a large mushroom-style kill switch in series with the ILDA cable, and use that switch to interrupt the interlock loop to kill the projector.)

Also if you were to pull the usb from the fb3 by accident would the laser shut down, as would it falsely create a disconnection from the idla connector because it has no power to it?

This is tricky, because the FB3 can be powered by an external power source or the USB cable. (It had to have that ability, since it's designed to also work as a stand-alone controller without a computer.) But assuming that you do *not* have an external power supply attached, then yes, removing the USB power will break the interlock connection. (It will also remove the +5 volts on the shutter line, causing the shutter to close.) Note that this is not "falsely creating a disconnection". If you loose power on the controller, you definitely want the projector to shut down. That's a safety feature.

If the FB3 is powered by an external source of power other than the USB cable and the USB plug is yanked out, I honestly don't know what the FB3 will do. I *suspect* that it will just kill the shutter; I don't know if it will also open the interlock loop or not. That's a question best posed to Pangolin.

Also if my laser gets power from the power supply through its special cable then I wouldn't be able to make the lasers ground go to my central grounding point because I would have to cut the cable right?

The modulation input to the laser driver has a positive input and a ground. The ground will be common to the DC ground of the power supply. (There's your ground.)

I am understanding that I need to keep my central grounding point separate from the case earth ground so I am guessing some type of block suspending above the case even though all it will have is pin 25 and the scanner grounds plus the shutter ground when I find one.

That is the ideal situation. (Note that you'll also have the laser power supply grounded to that, because the ground on the single-ended modulation input on the driver will be common with the DC ground of the laser power supply.) However, many people have built their projectors with ILDA pin 25 tied to all the above PLUS the case ground. Yes, this creates a ground loop. Yes, it's considered bad form. But very few people have had any problems with it.

To build your projector the way the wiring guide suggests, you have to electrically isolate your entire optical plate from the case ground, or else you have to islolate all your lasers from the optical plate. Neither task is easy, which is why a lot of people (including me) don't do it. No problems so far...

too bad the only parts i have right now are the scanners and the fb3..... almost tempted to hook them up and try to do a laser show with my pen laser :P wouldn't have blanking but it would still work right?

It would work just fine. (Except for the blanking, but that's not a big deal for a first attempt.)

Be *damn* careful wiring it up - it's easy to get something crossed when you're just using temporary jumpers, and if you get it wrong you might blow something. Tripple check everything before powering up. But if you are careful, it can be *loads* of fun to see things scanning for the very first time.

Wrap a rubber band around the pointer to hold down the switch, and make sure you've got it mounted so it won't roll away. Watch the alignment! It's easy to get a stray beam in the eye doing this! So be careful. (Did you get your goggles yet?) But if the pointer is relatively low power you should be OK.

At the very least, setting it up will familiarize you with the FB3 software, and that's always a good thing. You'll need to learn how to use all the tools if you want to create truly stunning effects, so go ahead and start learning now. (Plus you'll get a kick out of seeing a fan or a tunnel being scanned for the very first time. Definitely one of those "eureka" moments!)

You do have a fog machine, right? Better make sure you have it ready to go too!

Adam

[Doc]

because the ground on the single-ended modulation input on the driver will be common with the DC ground of the laser power supply.) However, many people have built their projectors with ILDA pin 25 tied to all the above PLUS the case ground. Yes, this creates a ground loop. Yes, it's considered bad form. But very few people have had any problems with it.

I had a weird problem with my projector when I first started using the FB3: In the scanned image; the blue and green output gradually faded to nothing from the centre of the Y axis down (both CNI modules), there was no problem with the laserwave reds.

I made a post in the help section about this and I think it was Jem that told me to disconnect the modulation grounds from ground and connect *just* them to pin 25. Voila problem solved!

Ian

[buffo]

Doc;

Is the projector chassis ground isolated from pin 25 in that projector? What about the PSU ground(s)? Are they isolated from the chassis ground as well?

Just curious... This is the first time I've ever heard of that problem, and it really sounds like a ball-buster! I know I would have been tearing my hair out anyway...

Adam

[Doc]

The PSUs are all star grounded to the central chassis ground, pin 25 is not grounded at the projector, only the modulation grounds connect to pin 25.

Having had this problem often makes me wonder if this is why some people are not getting full output from their FB3s?

And yes; it was a ball buster, I even thought at the time that it might be something to do with using p25, but thought ground id ground and dismissed the idea without checking.

Fail

[buffo]

The PSUs are all star grounded to the central chassis ground, pin 25 is not grounded at the projector, only the modulation grounds connect to pin 25.

Hmmm... The modulation inputs should be common with the DC ground on the power supplies, right? And if those were grounded to the chassis, then so was pin 25... Weird!

Having had this problem often makes me wonder if this is why some people are not getting full output from their FB3s?

I think that has more to do with how people are measuring the output of the FB3. (You need an oscilloscope to do it correctly.) Also, even if the modulation signal is a full +5 volts, remember that it drops to zero between frames. (Most people forget this.) So that can affect the average output power measurement of the laser, even if you're displaying a frame that has no blanked points.

And yes; it was a ball buster,

Fortunately for you, you didn't give up! Glad you were able to get it working correctly.

Adam

[Doc]

Hmmm... The modulation inputs should be common with the DC ground on the power supplies, right? And if those were grounded to the chassis, then so was pin 25... Weird!
I think that has more to do with how people are measuring the output of the FB3. (You need an oscilloscope to do it correctly.) Also, even if the modulation signal is a full +5 volts, remember that it drops to zero between frames. (Most people forget this.) So that can affect the average output power measurement of the laser, even if you're displaying a frame that has no blanked points.
Fortunately for you, you didn't give up! Glad you were able to get it working correctly.

Adam

Pin 25 was initially not connected, I figured that as the modules where chassis grounded; it would cause a ground loop. Thinking about it now; my blue module isn't in that grounding scheme as it's the combined CNI PSU and driver, the green however has a seperate driver.

I actually scoped the modulation output at more or less 5v, but then again there wasn't a problem with the output above the horizon so it was hard to tell.

Ian

[DMills]

I am not actually sure that that article is really correct, certainly if it was an audio device, AES48 would advocate bonding the ground connection on all external connectors to the case as close as possible to the connector, and then taking ONE connection from the case to the internal electronics reference rail.
Star grounding is a fix for problems caused by using single ended signalling, there is a reason the ILDA went for a fully differential scheme.

Given that as drawn all the modulation and scan amps have differential inputs, I have some issue with ground bounce being a problem at all (It would hint that something was rotten with the differential receivers). For certain, the connections between a differential receiver and the scan amps internal single ended circuitry can have ground bounce issues, but if the scan amp has a properly implemented differential input stage then the only reason to connect the 0V rail to the ILDA connector at all is to control the common mode range.

In an audio context but the same rules apply, Tony Waldron has a series of excellent articles on how to correctly implement a differential line stage (and many other interference and RFI issues) on his web site, and there is good stuff on Bill Whitlocks site (Ignore the transformer stuff, we need to pass DC).

Some of the THAT corp parts look seriously interesting for high CMRR input stages (Much better then an opamp and 4 resistors, also more expensive).

Regards, Dan (Who used to design broadcast gear for a living).

[buffo]

Dan:

The problem is that pin 25 is ground, but it runs the length of the ILDA cable back to the controller, which is then grounded through the host computer to the AC wiring ground at the wall.

Then you have the chassis ground of the projector, which is *also* grounded to the AC wiring ground at the wall, but probably at a completely different outlet.

Thus, a ground loop is just about inevitable, unless you lift the ground somewhere. The article suggests doing it between the lasers and the projector chassis.

Personally, If I have to do it, I lift the ground on the PC, since that also solves the ground loop problem for the audio output from the PC to the sound system. (I know, I know, ground lifts are bad... But it damn sure cures the 60 cycle hum of a ground loop!)

Adam

[DMills]

But the point is that if you do balanced lines right, the circulating current in the screens has very little effect, because it never gets into the single ended electronics reference.

See AES48 for the gory details.

Lifting the safety ground is not bad, it is potentially LETHAL. Grab a pair of suitable Lars Lundhal or Jensen transformers and build a line isolator box for the audio, on the ILDA side, do the interfaces right and it will just work (even with a few amps flowing in the screen).

Regards, Dan (In 230/400V land, so a little twitchy about safety ground connections).