FB3 hookup - help!!!

OKAY, I decided to use the "stock" FB3 connection to my scanners (ScanPro 30's), with no intermediate circuitry to complicate things.

Ignoring the interlocks and laser modulation inputs for the moment, the FB3 gives me the following connections across the ILDA connector:

X signal
X ground
Y signal
Y ground
Intensity signal
Intensity ground

My scanner amps have the following connections per amp:
(with power supply connected as indicated):

Signal in (-)
Signal in (+)
Signal ground
Scanner feedback
-24V
Gnd
Gnd
+24V


SO -
Can anyone who has hooked up the FB3, using similar connections, give a little tutoring on the proper connections to make here? I'm using the Pangolin LiveQUICK application with for my initial testing, with Buffo's recommended test frames from his scanner tuning tutorial. My initial displays have been nothing but an unrecognizable "glob", with VERY noisy scanners!! :eek:

Any assistance (before I blow something up!!!) would be appreciated - I don't even want to attempt tuning until I'm sure everything is hooked up correctly!!

Thanks in advance!!

Randy

Just connect X signal from the FB3 to signal in (+), X ground to signal in (-) and also you can connect ground on the FB3 to signal ground on the galvo drivers.

Intensity is for laser modulation and is nothing you need to worry about. Just use the regular channels.

The glob sounds worrying, how did you hook them up to get that?

Hi guys,

Stuka, are you geographically close to anyone else on PL, so that they can give you some help hooking this up? It is pretty easy, but somewhat difficult to communicate about it over a text-based forum.

But I do want to correct one thing, and it is something that is really subtle and easy to overlook. You should NOT!!! connect the "ground" of the DB25 ILDA signal to the "ground" of scanner amps!! In fact, you should not connect anything at all to the "ground" of a scanner amp (except for the "common" wire of the power supply).

Each scanner amp has a "ground". If you tie a signal wire (such as the so-called ground of the DB25 -- pin 25) to these grounds and also connect the power supply common to these grounds, then the scanner amps will actually have two separate ground paths, thus you have a "ground loop", but I really hate to use that phrase because it is way over-used. This will give you distorted graphics. The distortion can be subtle, but it is there.

The pictures that I take when I do a mod of the DT-40 (fully documented in another post) are not only with the mod, but also with the X- going into the X- of the amp, X+ going into the X+ of the amp, and NOTHING connected to the "ground" of the amp (except power supply common).

Then, after all of this, what you do is tie pin 25 on the DB25 to the POWER SUPPLY ground pin itself.

What you are trying to accomplish here is what's known as a "single point grounding scheme", otherwise known as a "star grounding scheme". I will let you guys look this up on Google or Wikipedia for more information...

Anyway, what you want is for all "ground" wires to meet at one, single place, and that place should be the power supply. Doing anything else will give you sub-optimal images.

Now, with this having been said, I bet a few of the professionals on this forum will re-wire their projector and get better performance. Stated another way -- I will be willing to bet that a good majority of "professionals" -- even those making laser projectors, do not know this...

Best regards,

William Benner

Bill -

Your grounding recommendations make sense.
What is your recommendation for the (-) amp signal inputs, when using a single-ended board such as the FB3?

OKAY - here are my initial results:

http://i222.photobucket.com/albums/d...r/DSCN2010.jpg

This is the square wave pattern recommended in Buffo's tuning tutorial!!:eek:
Using LiveQUICK, single laser, geometric correction set to 50% (I'm assuming that's the way you adjust scan angle?). Projector approximately 3 feet from wall/screen; image approximately 12" x 12"

FB3 connected to ScanPRO amps as follows:
X signal to X amp signal in (+)
X ground to X amp signal in (-)
Y signal to Y amp signal in (+)
Y ground to Y amp signal in (-)
BOTH scanner grounds & DB25 pin 25 connected to amp power supply common.

Any suggestions :confused:

PS -

The scanners are buzzing like a portable electric engraver while making this image!!

Quote:

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Originally Posted by Pangolin

But I do want to correct one thing, and it is something that is really subtle and easy to overlook. You should NOT!!! connect the "ground" of the DB25 ILDA signal to the "ground" of scanner amps!! In fact, you should not connect anything at all to the "ground" of a scanner amp (except for the "common" wire of the power supply).

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Thanks Bill. I've always wondered what the point of connecting the "signal ground" pin on the galvo amps was. I couldn't see any reason to do it, but it was one of those "everyone else is doing it, so it must be correct" things. Now begs the question, why do the amps have a "signal ground" in the first place?

Surely it's not intended for single-ended signals as that would leave X/Y- floating and that certainly doesn't seem like a good idea.

A question about the FB3 though; what is pin 25 (of the female DB25) connected to? Looking at the pin assignment in the manual one might think it's not connected to anything.

Here are a couple more photos, same conditions as previous image with one change - the DB25 ground is now disconnected from power supply common:

http://i222.photobucket.com/albums/d...r/DSCN2013.jpg

And in this one, the laser output is turned off in LiveQUICK:

http://i222.photobucket.com/albums/d...r/DSCN2012.jpg

And yes - the scanners still buzz while generating any image...

:mad: :confused: :(

someone has the link to this post...?

Thanks, JM

Quote:

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Originally Posted by Pangolin

Hi guys,

The pictures that I take when I do a mod of the DT-40 (fully documented in another post) are not only with the mod, but also with the X- going into

William Benner

---

Randy;

I can't see your pictures (blocked here at work), but it sounds like you've got a serious problem.

First, double-check that X signal on the FB3 is connected to X + on the scanner amp, and that X gnd on the FB3 is conencted to X - on the scanner amp, just as Bill posted above. (Obviously, the same thing goes for the Y axis)

Now turn your scan size down to around 15% and see what the image looks like. If it's still messed up, then there is another problem.

Adam

Yep, something definitely "ain't right" with the setup!!
I'll double-check all the connections when I get back this evening from playing Army.

Is it safe to assume that when working properly, the scanners should generally be operating with little or no noise?

Quote:

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Originally Posted by buffo

Randy;

I can't see your pictures (blocked here at work), but it sounds like you've got a serious problem.

First, double-check that X signal on the FB3 is connected to X + on the scanner amp, and that X gnd on the FB3 is conencted to X - on the scanner amp, just as Bill posted above. (Obviously, the same thing goes for the Y axis)

Now turn your scan size down to around 15% and see what the image looks like. If it's still messed up, then there is another problem.

Adam

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Check your wires, it looks like one is disconnected/broken.

Jim

Randy;

If you scanners are screaming, squealing, buzzing, or whining, that's usually a sign that they're being overdriven. A little bit of noise once in a while is OK, but if they are constantly making these sounds, and *especially* if hearing the sound makes you wonder if you are overdriving them, then rest assured that YOU ARE OVERDRIVING THEM. :D

Double-check everything and then post back here with your results.

Adam

I hate that statement - no offense Adam :D but my DT40 Pros even operating at ILDA specs squeal quite a bit more than I expected - and still do. I was terrified when I first got them because everyone said they **shouldn't** make much noise at all. Well for me almost ANY pattern displayed will produce enough noise to hear it over my laptop speakers. Maybe I'll borrow a dB meter from work - or buy a nice one just to get a good idea of the amount of noise I am getting. That would have to do for the time being until I meet a fellow PhotonLexiconer who has been around the block a few times. Well either way - I don't think mine are being over driven and they have plenty of usage on them :P

-Max

Here's an interesting twist, thanks to a tip I received in e-mail from Barry ("dazebtwn" here on the forums) -

It appears that the documentation that came with my FB3 depicts the FB3 motherboard to DMX daughterboard connection, NOT the DB25 projector connections, which do appear to conform to the ILDA standard.
It's a little misleading the way it's depicted in the documentation - at least for us noobs!!

Per Barry's tip, (and follow up from tocket - thanks guys!!) I followed the ILDA pinout (at least for the X+ and Y+ amp connections), and I now appear to have a working set of scanners! I still have some testing and fine-tuning to do with the remaining connections from the FB3, but it looks like I'm heading in the right direction.
Sweet - scanners working, and nothing melted!! :D

More to follow as things progress.....

Oh, the pinout in the FB3 manual is not for the DB25 female. That one has the standard ILDA pinout. The pinout is for that red internal connector on the board. Looking at the flat cable between the two it is fairly evident that the pinouts are different. ;)

It is interesting what you did though, as you had connected X+ correctly (pin 1 in both configurations), but Y+ of the amp was wired to Intensity signal of the FB3 and Y- to Interlock A. This still produced a vertical line with laser output off, which indicates that interlock A is not a fixed voltage. I did not know this!

I'm certain things will go much better now that you know what's wrong and how to fix it. Looking forward to seeing the results and I hope your scanners did not take any damage from this.

Tocket;

Interlock A should have been unconnected. The interlock pins simply make a loop between A and B inside the controller. They're not connected to anything else, and the controller doesn't put any voltage on those pins. At best, it would have been floating at whatever potential the scanner amp Y - pin was at.

My guess is that he was getting the Y axis to move based on the variable signal on the positive intensity signal line. I don't think the interlock line had anything to do with it.

Still, good call on figuring out that he was using the pinout for the daughterboard connector and not the ILDA port!

Max:

I think you have very sensitive ears! I listened to the recording you made of you playing guitar, and I couldn't hear any of the noise sources you complained about. So maybe to you, it does sound like your scanners are screaming.

They always make a little noise when operating, but usually that noise can't be heard over the sound of the projector case fans. (Then too, the projector case itself serves to muffle any sounds coming from within.)

I will admit that of all the scanners I've tested, the DT-40's (and even the newer DT-40 pro's) seem to be the loudest. They make more noise than any other scanner I've ever worked with. But when you start pushing them, they *really* get loud! That's when you're in the danger zone. (Fortunately, most of the time the poly switch will trip and save your ass.)

It may be that you are so used to looking for abnormal sounds that you can hear the scanners even when they're operating normally, and even when the fans on the projector are trying to drown the sound out. You are also younger, so your hearing is likely to be much more accute than mine. Given all the above, I'd have to say that your scanners are probably just fine - even if they do sound noisy to you.

But when an old fart like me can still hear the scanners squealing, then something is wrong! :D Randy has heard my projector when it's running, and it doesn't sqeal, so based on that (plus what we now know about the wiring mixup he had), I'd say that his scanners probably *were* making some unnatural sounds...

Adam

Hey, I'm part of that "old fart" group, and after 20+ years of exposure to turbine engine noise, I was definitely concerned about the sounds coming from my scanners!! They weren't just "unnatural" sounding - it was downright scary!!! :eek:

Thankfully, all ends well -
I was made aware of my noob misinterpretation errors, and I'm happy to say I successfully generated all the images that came with LiveQUICK and LivePRO - at least with single-color, non-blanking lasers (that part isn't hooked up yet!!) And best I can tell, nothing was melted, fried, or otherwise damaged beyond repair in my futile, error-filled initial attempts at hooking up my scanners!! :D

Thanks to everyone who chimed in and guided me in the right direction :)

Randy

Good to hear that your scanners are working fine! I hate killing expensive stuff because of stupid mistakes (and it happens to me a lot). :(

Quote:

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Originally Posted by buffo

Interlock A should have been unconnected. The interlock pins simply make a loop between A and B inside the controller. They're not connected to anything else, and the controller doesn't put any voltage on those pins. At best, it would have been floating at whatever potential the scanner amp Y - pin was at.

---

Ah... yes, the interlock test circuit is of course on the projector side of things. Since Interlock B is on pin 17 it was probably left floating. The intensity pin should have been at a fixed voltage since laser output was off (the last picture).

I know that op-amps can do strange things when you leave one of their input pins floating, but I wouldn't have expected anything like that. :confused:

Quote:

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Originally Posted by buffo

I think you have very sensitive ears! I listened to the recording you made of you playing guitar, and I couldn't hear any of the noise sources you complained about. So maybe to you, it does sound like your scanners are screaming.

They always make a little noise when operating, but usually that noise can't be heard over the sound of the projector case fans. (Then too, the projector case itself serves to muffle any sounds coming from within.)

I will admit that of all the scanners I've tested, the DT-40's (and even the newer DT-40 pro's) seem to be the loudest. They make more noise than any other scanner I've ever worked with. But when you start pushing them, they *really* get loud! That's when you're in the danger zone. (Fortunately, most of the time the poly switch will trip and save your ass.)

It may be that you are so used to looking for abnormal sounds that you can hear the scanners even when they're operating normally, and even when the fans on the projector are trying to drown the sound out. You are also younger, so your hearing is likely to be much more accute than mine. Given all the above, I'd have to say that your scanners are probably just fine - even if they do sound noisy to you.

But when an old fart like me can still hear the scanners squealing, then something is wrong! :D Randy has heard my projector when it's running, and it doesn't sqeal, so based on that (plus what we now know about the wiring mixup he had), I'd say that his scanners probably *were* making some unnatural sounds...

Adam

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Yeah, I agree, you are probably right. This is of course one of the reasons I almost ALWAYS wear earplugs at shows. Some of the shows I have seen lately are at scary volumes - of course the ear can recover to a degree, but I enjoy my hearing.

I just have a hard time trying to quantify the term 'squealing' in a text based forum. Maybe I will use the same recording setup to record the noise from the DT40 Pros. I just wont use any noise canceling on that track :D

Like I said regarding the guitar playing I am my worst critic, I spent a good hour or so eliminating all the noise out of the setup before I even put a CD in the drive.

-Max

Quote:

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Originally Posted by Pangolin

Hi guys,
But I do want to correct one thing, and it is something that is really subtle and easy to overlook. You should NOT!!! connect the "ground" of the DB25 ILDA signal to the "ground" of scanner amps!! In fact, you should not connect anything at all to the "ground" of a scanner amp (except for the "common" wire of the power supply).

---

With all due respect for the your knowledge Bill, but I think you should not generalize and to affirm that "NOT Should connect the "ground" the DB25 ILDA signal to the "ground" of scanner amps" for any signal connections, because each wiring is a situation specifies, due to the scanner type, amps, power supply etc... contained in the projector and therefore, I suggest to connect the amps ground, testing and verifying the performance of the projections in several conditions and in agreement with the results, to connect or not, reminding that Cambridge Technology, world leader in the production of scanners and servo drivers, recommends to connect the ground for Analog Differential Input Configuration, according to passage (below) of the manual of Micromax 671 Series, pag.46
"There should be the direct ground connection from the signal source to the Pin 2 on the input connector (J1, Pin2 - ground) on the shield of the wire or the separate wire. If shield wire is not available, use a third wire then twist all wires to provide some level of shielding", still recommending to connect wire between both grounds on specific points of the servo drivers (Dual Axis System), to avoid strong coupling between channels, reducing crostalk between the two channels caused by high ground currents.

Best Regards

Carlos

Quote:

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Originally Posted by Lasershow

... therefore, I suggest to connect the amps ground

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Ummm. aha. And, for the record, may we all know who "I" is? Could you please state, for the benefit of the members here on PL, your credentials, including any degrees you hold, any patents you hold, and any accolades you have won as a testamente of your own ability to make such a recommendation?

Quote:

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Originally Posted by Lasershow

recommends to connect the ground for Analog Differential Input Configuration, according to passage (below) of the manual of Micromax 671 Series, pag.46

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It's easy to fall into a trap and take things out of context.

With respect to why Cambridge makes the recommendation they do in their manual, and why there are three connections on a scanner amp -- if you have only a single scanner amp, then you might get away by connecting your "signal ground" to the scanner amp's ground. But for everyone here doing two-axis laser graphics and beam shows, you have two amps, not just one, and connecting your "signal ground" to the ground connection of both scanner amps will cause this kind of "ground loop" (I hate that term because it is way over used), and the X amp will experience "ground bounce" when the Y amp undergoes hard acceleration, and vice-versa. The result is crappy images (to some extent), the extent depends on the gauge of the wire, the degree of acceleration, and other factors. You can avoid all of this by making only one single ground connection *somewhere*, and the best place to do that is the common ground connection at the power supply itself.

For the record, I have nothing to prove. If you want to follow my recommendations, it doesn't make me feel any better about myself. And if you don't take my recommendations, it won't make me feel any worst about myself. I am confident in who I am as a person, and confident in my abilities as an engineer. Likewise, there are those who have known me for a very long time and, lets just say my reputation preceds me. For those who don't know me, I have the technical certifications, patents, awards, and other accolades (letters of commendation from heads of state) to prove that, by and large, I know what I am talking about.

Of course, I can always make mistakes (more about this in another post). I myself have made the very same recommendation that Cambridge made years ago (thanks for pointing this out DZ -- I will change my own docs). Today I count those older recommendations as a mistake, and my latest recommendation is to connect the DB25 to the ground of the power supply and NOT directly to the amps. I have my reasons, and in the lab, I can show you or anyone else the difference.

Bottom line -- people (and companies -- BIG ONES) send me scanners to improve. The people here on PL can universally tell you that when they get back their scanners from me, they are wired the way I am saying in these recent posts. And wiring these scanners is the very LAST thing that I do -- so the wiring is not done out of prejudice, or wanting to prove that I am right. The fact is, these systems don't look as good as they do, unless they are wired the way I say. And those are the facts.

In any event, anybody here is free to choose whatever wiring method they want. On a personal level, I don't care. You aren't going to hurt my feelings if you don't follow my recommendations, and aren't going to stroke my ego if you do. Aside from just wanting every laser show to appear as good as it can (for reasons stated in other posts), I really don't care. Especially if you are a competitor!! Definitely don't follow my recommendations !!! :D

On a hobbyist level, maybe we can just change the statement a bit. The wiring I suggest is "what works for me". I believe it will also work for everyone else, and recently, big projector manufacturers have changed their designs, so they believe me too. You can try it, and see if it works for you too. If it does, then great. If it doesn't, then figure it out for yourself. Really that's the spirit here on PL -- figuring things out for yourself (hopefully, with the help of others), and then sharing your experiences.

As a final note, can I call on some of those for whom I have tuned (and changed the wiring on) their scanners, to post in this forum about what your scanners looked like before, and after they visited Pangolin? Sure, there are many changes done, but the wiring is one of the changes that leads to the pretty pictures :D.

Best regards,

William Benner

OK, I think it is time for a WIRE OFF!! OK gents, display a pic with wiring one way and snap a photo. Change your wiring and snap another. It's time to put the copper where the mouth is. :)

Actually, as silly as it sounds, I think it is actually a good test to see the differences. But, of course I don't really expect anyone to do this since it would be a bit of a pain in the neck to do.

Gary - If you want to see the huge renovation I have made check out this thread...

http://www.photonlexicon.com/forums/...nning+building

That thread takes me from knowing very little about Laser Projectors to where I am currently standing with my projector as of about yesterday :)

I am so happy with my current set up I fired it up first thing this morning along with the fogger and got ready for work with the diffraction grating lighting up the room :D

Bill in first point, I want to leave a very clear thing that I am not challenging you, because for the way that you wrote, it seems that you were offended with my placement, I only put in the post the opinion of Cambridge that in the moment I share, but that can be changed, reminding you that the basic purpose of the PL forum is exactly to try to explain doubts and/or to solve problems remotely, in other words, at the distance and to change ideas to learn several subjects, besides the technical discussions, I don't want to discuss and to "fight" with you, I only want to change ideas and knowledge, OK?

Quote:

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Originally Posted by Pangolin

Ummm. aha. And, for the record, may we all know who "I" is? Could you please state, for the benefit of the members here on PL, your credentials, including any degrees you hold, any patents you hold, and any accolades you have won as a testamente of your own ability to make such a recommendation?

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I am an Engineer formed in 1984 and I work with Laser Light Shows about 25 years and therefore I have a lot of experiences in field and I think there is no need to tell my credentials in full detail, unless you want to know particularly, because this is not the purpose of the forum and the recommendation that I did is orientation of Cambridge Technology, see attached files

Quote:

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With respect to why Cambridge makes the recommendation they do in their manual, and why there are three connections on a scanner amp -- if you have only a single scanner amp, then you might get away by connecting your "signal ground" to the scanner amp's ground. But for everyone here doing two-axis laser graphics and beam shows, you have two amps, not just one, and connecting your "signal ground" to the ground connection of both scanner amps will cause this kind of "ground loop" (I hate that term because it is way over used), and the X amp will experience "ground bounce" when the Y amp undergoes hard acceleration, and vice-versa. The result is crappy images (to some extent), the extent depends on the gauge of the wire, the degree of acceleration, and other factors. You can avoid all of this by making only one single ground connection *somewhere*, and the best place to do that is the common ground connection at the power supply itself.

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The recommendation of Cambridge is for Dual Axis System with Analog Differential Input (+ input, - input and GND) and that there should be the direct ground connection from the signal source to the Pin 2 on the input connector (J1, Pin2 - ground) on the shield of the wire or the separate wire. If shield wire is not available, use a third wire then twist all wires to provide some level of shielding and still connecting wire ground between specific points of the boards, to avoid strong coupling between channels and also to reduce crostalk between the two channels caused by high ground currents (power connections), you see attached files ElectricalDetails.jpg in the bottom of the item 7.3 Command Input Wiring and also in SignalConnectionsDiagram.pdf

Quote:

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For the record, I have nothing to prove. If you want to follow my recommendations, it doesn't make me feel any better about myself. And if you don't take my recommendations, it won't make me feel any worst about myself.

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I don't want you to prove anything and nor that the your recommendation makes you to feel better or worst about yourself, I only want that technically, be discussed by several members this subject, to obtain a conclusion.

Quote:

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I am confident in who I am as a person, and confident in my abilities as an engineer. Likewise, there are those who have known me for a very long time and, lets just say my reputation preceds me. For those who don't know me, I have the technical certifications, patents, awards, and other accolades (letters of commendation from heads of state) to prove that, by and large, I know what I am talking about.

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I am not doubting of your abilities, reputation and nor than you are talking and I don't want to say anything, that it changes your opinion and once again I only want to discuss the subject technically.

Quote:

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Of course, I can always make mistakes..... I have my reasons, and in the lab, I can show you or anyone else the difference.

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All of us makes mistakes, we are not still perfect and Ok, I going to USA, I will inform you for you to show me the difference

Quote:

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In any event, anybody here is free to choose whatever wiring method they want. On a personal level, I don't care. You aren't going to hurt my feelings if you don't follow my recommendations, and aren't going to stroke my ego if you do. Aside from just wanting every laser show to appear as good as it can (for reasons stated in other posts), I really don't care. Especially if you are a competitor!! Definitely don't follow my recommendations !!! :D

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Each person can choose what to think better for itself and I don't want to hurt your feelings or to stroke your ego with relationship on to follow your recommendations, what I want is to discuss this subject technically and I don't feel your competitor and yes your partner of PL forum and who knows a future customer.......

Quote:

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On a hobbyist level, maybe we can just change the statement a bit. The wiring I suggest is "what works for me". I believe it will also work for everyone else, and recently, big projector manufacturers have changed their designs, so they believe me too. You can try it, and see if it works for you too. If it does, then great. If it doesn't, then figure it out for yourself. Really that's the spirit here on PL -- figuring things out for yourself (hopefully, with the help of others), and then sharing your experiences.

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I think should not have differences and to change the statement a bit on a hobbilist or professional level, because the technical information has to be same for everyone.
I can try and to verify if it works for me and to talk for you the result, but could you send me a Wiring Diagram for my scanners and servo boards?
I also think the spirit here of the PL forum is to help the other members and to share our experiences.

Quote:

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As a final note, can I call on some of those for whom I have tuned (and changed the wiring on) their scanners, to post in this forum about what your scanners looked like before, and after they visited Pangolin? Sure, there are many changes done, but the wiring is one of the changes that leads to the pretty pictures :D.

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Ok, I would like you to call then some members that changed their wiring for them to talk their experiences and to share with the other members here of the PL forum

Best Regards

Carlos

I agree that we don't want a flame war! But I do think that this is an interesting topic, and I would like to hear more on the subject.

I spoke with Bill Benner about this issue last week on the phone. Based on our conversation, I decided to perform some tests on my projector.

I have a Pangolin QM-2000 intro board connected to my home-made RGB projector. The scanners are DT-40 pro's from Jian. They are powered by a pair of 24 volt power supplies in parallel. The + terminal of one PSU is connected to the - terminal of the other PSU, giving me a +24 volt rail, an isolated ground rail, and a -24 volt rail. The power supplies are each rated for 5.5 amps continuous output, which is more than double the current that the standard DT-40 scanner power supply can deliver.

I have pin 25 on the ilda connector wired to the ground input on the scanners. This is also connected to the negative blanking leads on all lasers in the projector. However, it is *not* conencted to the ground on the power supply feeding the scanners.

Of course I have X+ wired to the X+ input ont he amp, and X- connected to the X- input, and the same thing for the Y amp.

Last night I disconencted the ground wire going to the scanner input. I did not see any change in the scanned image. I loaded up the quadrature square wave pattern and collapsed the Y axis to zero percent size. Then I looked along the now-horizontal line that was being scanned and watched for any signs of movement in the Y axis. I found none.

Then I reverse the settings so the X was collapsed and Y was at 100%. Again I looked for any movement in the X axis, and again, I found none.

Finally, I re-connected the ground wire to the input to the scanner amps and ran both tests again. I still did not see any sign of noise.

In the next day or two, I plan to conenct a ground wire from the scanner amp PSU ground to pin 25 and then repeat these tests again. I'll try to post some pictures as well.

Adam

I am guessing that probably still had between the two. Could you check with an ohmmeter to see if there are any noticeable changes in resistance?

Good idea, Gary. I'll check the ground potential on that scanner amp PSU (with the pin-25 connection to the signal input lifted) the next time I power up the scanner, and I'll post my results here.

Adam

Quote:

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Originally Posted by buffo

I have a Pangolin QM-2000 intro board connected to my home-made RGB projector. The scanners are DT-40 pro's from Jian. They are powered by a pair of 24 volt power supplies in parallel. The + terminal of one PSU is connected to the - terminal of the other PSU, giving me a +24 volt rail, an isolated ground rail, and a -24 volt rail. The power supplies are each rated for 5.5 amps continuous output, which is more than double the current that the standard DT-40 scanner power supply can deliver.

I have pin 25 on the ilda connector wired to the ground input on the scanners. This is also connected to the negative blanking leads on all lasers in the projector. However, it is *not* conencted to the ground on the power supply feeding the scanners.

Of course I have X+ wired to the X+ input ont he amp, and X- connected to the X- input, and the same thing for the Y amp.

Last night I disconencted the ground wire going to the scanner input. I did not see any change in the scanned image. I loaded up the quadrature square wave pattern and collapsed the Y axis to zero percent size. Then I looked along the now-horizontal line that was being scanned and watched for any signs of movement in the Y axis. I found none.

Then I reverse the settings so the X was collapsed and Y was at 100%. Again I looked for any movement in the X axis, and again, I found none.

Finally, I re-connected the ground wire to the input to the scanner amps and ran both tests again. I still did not see any sign of noise.

In the next day or two, I plan to conenct a ground wire from the scanner amp PSU ground to pin 25 and then repeat these tests again. I'll try to post some pictures as well.

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Ok, Adam thank you for the confirmation, because each installation will have an performance different, due to the scanner type, servo driver and power supply of the wiring with DB25 ILDA'S ground (Pin 25) connected for Scanner Amps's ground, as I informed in the previous post, therefore it is necessary to test for each installation particularly and to verify the results, to decide if the ground will be tied or not.
This is also my recommendation, shared with to Cambridge, until that somebody proves me differently.

Thanks

Carlos

Ok - I did some more tests. Unfortunately, the results aren't very conclusive...

First, Gary - I checked to see if there was any potential difference between the isolated ground of the Scanner amp PSU and earth ground. There was no difference.

However, as Bill mentioned earlier, since just about every device in the projector is grounded to it's case, which is bolted to the optical table, which is already at ground potential, I suppose it's not surprising that I didn't get any reading other than zero. (I didn't disconnect the scanner amps from the PSU, so my guess is that they were grounded through the scanners to the optical plate.)

Just for grins, I connected a ground wire from pin 25 to the ground on the scanner amp power supply. Then I removed the ground from the scanner input. No change in scanned images. (I looked at the test pattern, as well as the quadrature square wave pattern with first the X axis collapsed, and then the Y axis collapsed.)

Then I connected pin 25 back to the input connector on the scanner amp, and left the other ground wire from pin 25 connected to the power supply. Still no change.

Finally, I removed the ground wire going to the scanner amp power supply and left pin 25 connected to the scanner amp input. Still no change.

I should note that in my projector, the red, green and blue modulation signals are connected with the positive leads going to the R+, G+ and B+ pins, and the negative leads are connected to pin 25.

If I get *really* ambitious, I might yank those negative leads loose from pin 25 and connect them to the R-, G-, and B- pins, just to see if it makes any difference. But I don't see that happening any time soon. (I've got another big project in the works at the moment, and I still haven't done my taxes yet!:rolleyes:)

Adam

I am willing to bet that the - RGB pins on your DAC are tied to ground so it won't make a difference which ones you use. But, it would be a good idea to connect then to the - RGB pins in case you happen to switch DACs sometime in the future and it doesn't have them tied to ground. ;):p:(

Quote:

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Originally Posted by buffo

Ok - I did some more tests. Unfortunately, the results aren't very conclusive...

First, Gary - I checked to see if there was any potential difference between the isolated ground of the Scanner amp PSU and earth ground. There was no difference.

However, as Bill mentioned earlier, since just about every device in the projector is grounded to it's case, which is bolted to the optical table, which is already at ground potential, I suppose it's not surprising that I didn't get any reading other than zero. (I didn't disconnect the scanner amps from the PSU, so my guess is that they were grounded through the scanners to the optical plate.)

Just for grins, I connected a ground wire from pin 25 to the ground on the scanner amp power supply. Then I removed the ground from the scanner input. No change in scanned images. (I looked at the test pattern, as well as the quadrature square wave pattern with first the X axis collapsed, and then the Y axis collapsed.)

Then I connected pin 25 back to the input connector on the scanner amp, and left the other ground wire from pin 25 connected to the power supply. Still no change.

Finally, I removed the ground wire going to the scanner amp power supply and left pin 25 connected to the scanner amp input. Still no change.

I should note that in my projector, the red, green and blue modulation signals are connected with the positive leads going to the R+, G+ and B+ pins, and the negative leads are connected to pin 25.

If I get *really* ambitious, I might yank those negative leads loose from pin 25 and connect them to the R-, G-, and B- pins, just to see if it makes any difference. But I don't see that happening any time soon. (I've got another big project in the works at the moment, and I still haven't done my taxes yet!:rolleyes:)

Adam

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Hello Adam

The results of their tests, show that it doesn't have differences of potentials of the two grounds and then they don't create the circulation of electric current and then the ground loop doesn't induce noises, because his equipment was projected and built appropriately and consequently the Images of the projector, are projected without distortions and then for his projector and installation, including power supplies, scanners, scanners amps, leads with quality and good gauges, etc... it don't have any interference and YES you should leave connected the ground of the DB25 ILDA Signal to the ground of scanners amps for you protect it in case there is the need of some escape of current unwanted.

Then, the ground loop is not a problem and it does not cause troubles when all of the following thing are true:
I) - None of the wires in the loop carry any current
II) - The loop is not exposed to external changing magnetic fields
III) - There is no radio frequency interference nearby

Conclusion: Nobody can generalize and to affirm that we should not connect the "ground" the DB25 ILDA signal to the "ground" of scanner amps", because each wiring is a different situation, specifies and particular and therefore we needed first to test and to verify the final performance for later decide in connecting or not.

Best Regards

Carlos

Hi guys,

If you have a dual-axis amp (as maybe Lasershow may have), then, almost by definition, there won't be a difference between the two axis because... it's all one amplifier. But on these Chinese systems where they are implemented as two, separate, single-axis amps, we definitely see a difference, especially since the Chinese often supply power supplies and wiring with their systems, neither of which are very good...

Also, I will point out two excerpts from the manual that Lasershow seems to covet so much. You will see wording "can cause problems which are hard to diagnose", and even more important "This reduces crosstalk between the two channels caused by high ground currents". The latter implies that there will be "crosstalk between the two channels" no matter what.

If you do it my way, the crosstalk won't matter because it will be cancelled out by the differential receiver of the channels (with no common ground connection). If you do it another way, then, as Cambridge alludes... your results may vary, depending on the thickness of the wire used for ground, and other factors I mentioned in a previous post.

And there is one more factor. The difference will be much more noticable on amps which use single-ended scanner drive, rather than H-bridge drive, because with H-bridge drive there is almost zero ground current (at least in theory).

In other words... "your milage may vary"...

As for "generalization", we can certainly generally say that a single-point grounding scheme is preferred, and if you don't believe me, just consult the internet... A single-point grounding scheme will always give you consistent and superior results, no matter how thick your wiring is, or what kind of power supply or output system your scanner amp has. If you're a betting man, do it my way :D.

But if you don't want to follow my recommendations, then that's OK. Not everyone has to have perfect images :D.

Bill

Quote:

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Originally Posted by Pangolin

Also, I will point out two excerpts from the manual that Lasershow seems to covet so much. You will see wording "can cause problems which are hard to diagnose", and even more important "This reduces crosstalk between the two channels caused by high ground currents". The latter implies that there will be "crosstalk between the two channels" no matter what.

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I don't covet the manual, I usually try to follow the manufacturer's orientations, mainly of renowned companies and the excerpt "Can cause problems which are hard to diagnose", it refers the contact resistance in the crimp caused by dirty or oxidized pins or wire, or by a worn or improperly used tool, or by excessive stress on the wire and "This reduces crosstalk between the two channels caused by high ground currents", it refers the Power Connections and it is informing to connect a short, heavy ground wire between the two boards to avoid strong coupling between channels and the CT information are appropriate.

Quote:

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As for "generalization", we can certainly generally say that a single-point grounding scheme is preferred, and if you don't believe me, just consult the internet... A single-point grounding scheme will always give you consistent and superior results, no matter how thick your wiring is, or what kind of power supply or output system your scanner amp has.

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It is evident whenever, "ground loops" there are in an installation, resulting in interferences/noises, will be necessary eliminate them and there are four basic methods to dealing with grounds: single point, multiple point, floating, and telescoping shield, each has specific advantages in different types of installation.

Carlos

The excerpts I took from the Cambridge manual are entirely relevant for ground situations, just as they are for bad crimps and connections. But if you don't understand, that's fine. Really.

For what it's worth, Pangolin is also "world renowned", and I personally have consulted for Cambridge on numerous projects, including on the 6800 and 6215 scanner projects and related amps.

And for what it's worth, I think the recommendations that you are following come from the very same process that produced what were the same recomendations in our own documentation (thanks for pointing it out DZ) -- basically it was a careless and quickly-done documentation. I'll get confirmation from Cambridge on this point. Maybe if it comes from them you will respect it more?

As an aside, from your attitude (and yes, I can often tell who is using what software from the attitude expressed) I imagine that you must not be using Pangolin software, and thus, half jokingly I would say that you don't deserve the great images that a single-point grounding scheme could provide. But this is of course merely a jovial comment. I have helped out lots of Laserfreak and PL members to get the best images they can, regardless of whether or not they are using Pangolin software. Ultimately, and through trickle-down theory, everyone wins if everyone has good looking images. That's why I am so passionate about helping people -- even you Carlos :D.


Best regards,

William Benner

Quote:

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Originally Posted by Pangolin

The excerpts I took from the Cambridge manual are entirely relevant for ground situations, just as they are for bad crimps and connections. But if you don't understand, that's fine. Really.

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I understood and I only explained with details the two excerpts, mentioned by you.

Quote:

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For what it's worth, Pangolin is also "world renowned", and I personally have consulted for Cambridge on numerous projects, including on the 6800 and 6215 scanner projects and related amps.

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I know that Pangolin is also a renowned Company and is evident that is important your comment.

Quote:

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And for what it's worth, I think the recommendations that you are following come from the very same process that produced what were the same recomendations in our own documentation (thanks for pointing it out DZ) -- basically it was a careless and quickly-done documentation. I'll get confirmation from Cambridge on this point. Maybe if it comes from them you will respect it more?

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As far as I know, the Cambridge Manuals are revised and corrected, because that is printed in the manuals and I usually respect the manufacturers' information and when I don't agree, I try to elucidate my doubts and you inform me, please if CT changes the recommendations on this point.:)

Quote:

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As an aside, from your attitude (and yes, I can often tell who is using what software from the attitude expressed) I imagine that you must not be using Pangolin software, and thus, half jokingly I would say that you don't deserve the great images that a single-point grounding scheme could provide. But this is of course merely a jovial comment. I have helped out lots of Laserfreak and PL members to get the best images they can, regardless of whether or not they are using Pangolin software. Ultimately, and through trickle-down theory, everyone wins if everyone has good looking images. That's why I am so passionate about helping people -- even you Carlos :D.

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It is evident that I want great images and I also like of helping people a lot and I am happy in knowing that you can help me, I thank you very in advance and any doubts that I can have, I will consult you.

Best Regards

Carlos

Hi Carlos,

Thanks for the comments. I genuinely appreciate your attitude. And I am not trying to be an asshole, although it might come across that way in a low-bandwidth medium like email or forum text.

Now lets get down to business. I have had an email exchange about this topic with Mike Thanos at Cambridge. I am not sure what Mike's current title is at Cambridge (he used to be called "Engineering Manager", but he might have a more prestigious title now), but he is basically my counterpart there. Mike has been involved with Cambridge certainly since they began making scanners around 20 years ago, and before that, he worked at General Scanning. Although he is too modest to say so himself, I would consider him to be a master circuit designer. If memory serves, Mike actually wrote the original manuals for the 6800 and for the original Cambridge CB6580, and his wording has probably been propagated by whoever it is that is writing Cambridge manuals today.

I discussed this situation with Mike, along with my current "single point grounding scheme" recommendations. And, for space reasons, while I don't want to re-print the entire email exchange, I will point out a few relevant points in his response. Mike wrote:

> You are right on every point. We call this "coupling" and it works
> exactly as you've described. In fact, there are a number of ways to
> solve this. One way is to keep everything differential. But as you
> know, some people do use oscilloscopes to view signals. As soon as
> they do this, they add a ground loop.

Mike went on to show me the very same "Signal connections" PDF file that you had attached to your earlier post. Somehow I completely overlooked that PDF, but actually the answer is sitting right there in that document.

If you look at the diagram, it shows the shield of the cables going into pin 2 of the amp. But on the diagram, pin 2 is labeled as "N/C" which means "no connection". Now, here's the funny part. Pin 2 is not "no connection" it is the signal ground.

It was the intention to communicate that you DON'T connect anything to the signal ground of the scanner amp, although that gets a bit lost in the diagram PDF you have. Cambridge is in the process of updating that diagram as we speak, and will remove the wire going into pin 2, showing that the shield only protects the wires themselves, but should not make an actual physical connection to the scanner amp itself.

Also, I have taken another look at the picture of the printed wording from the Cambridge manual you have in your earlier post. This APPEARS to have some conflicting information, but it really doesn't. Unfortunately, the words on that page only make COMPLETE sense when they are interpreted in the context of another diagram in the Cambridge manual called "Power connections". This other diagram shows two separate, single-voltage, power supplies used, not one dual-voltage power supply as is commonly distributed with Chinese scanners. Cambridge chose to show a particular connection methodology whereby the two separate power supplies are connected to the two separate scanner amps, but I personally don't like that connection methodology very much, and it just about requires this separate heavy-gauge wire to be used.

Incidentally, the wire Cambridge discusses there really isn't related to this matter. It's there for power reasons, not for signal reasons. Nevertheless, we will see if Cambridge updates this document as well, to show that, for clarity purposes, the power supply connections could be made in a simpler way with ground connections meeting at the power supply, rather than using this separate heavy gauge wire.

Whew!! A lot of words for just one simple thing. Although this subject has been contentious and controversial (sheesh) I am glad that it has come up because it gives us a chance to review AND CORRECT our own documentation. (Thanks for pointing out these bugaboos DZ!)

And with all of this having been written, my recommendation stands. Don't connect anything to the "signal ground" of the scanner amps, and connect DB25 pin 25 only to some common, single point in the projector, preferably at the power supply.

Best regards,

William Benner

Quote:

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Originally Posted by Pangolin

Hi Carlos,

Thanks for the comments. I genuinely appreciate your attitude. And I am not trying to be an asshole, although it might come across that way in a low-bandwidth medium like email or forum text.

---

My comments are with the intention of helping and you don't worry, because you are not being an asshole.

Quote:

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Now lets get down to business. I have had an email exchange about this topic with Mike Thanos at Cambridge. I am not sure what Mike's current title is at Cambridge (he used to be called "Engineering Manager", but he might have a more prestigious title now), but he is basically my counterpart there. Mike has been involved with Cambridge certainly since they began making scanners around 20 years ago, and before that, he worked at General Scanning. Although he is too modest to say so himself, I would consider him to be a master circuit designer. If memory serves, Mike actually wrote the original manuals for the 6800 and for the original Cambridge CB6580, and his wording has probably been propagated by whoever it is that is writing Cambridge manuals today.
I discussed this situation with Mike, along with my current "single point grounding scheme" recommendations. And, for space reasons, while I don't want to re-print the entire email exchange, I will point out a few relevant points in his response. Mike wrote:

---

Mike Thanos is VP of Engineering and there in Cambridge also has the Engineer Mike Danos and if you can, send the entire email exchange of Thanos for my e-mail.

Quote:

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> You are right on every point. We call this "coupling" and it works
> exactly as you've described. In fact, there are a number of ways to
> solve this. One way is to keep everything differential. But as you
> know, some people do use oscilloscopes to view signals. As soon as
> they do this, they add a ground loop.

---

If I understood correctly, Thanos says that to solve the ground loop, one way is to keep everything differential signal, in other words, the input configuration "Analog Differential", using + input, - input and maybe (????) ± input return GND.

Quote:

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Mike went on to show me the very same "Signal connections" PDF file that you had attached to your earlier post. Somehow I completely overlooked that PDF, but actually the answer is sitting right there in that document.
If you look at the diagram, it shows the shield of the cables going into pin 2 of the amp. But on the diagram, pin 2 is labeled as "N/C" which means "no connection". Now, here's the funny part. Pin 2 is not "no connection" it is the signal ground.

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I saw this in the diagram and I think N/C means "No Charge", i.e. no electric charge, because it is ground, please confirm this with Thanos.

Quote:

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It was the intention to communicate that you DON'T connect anything to the signal ground of the scanner amp, although that gets a bit lost in the diagram PDF you have. Cambridge is in the process of updating that diagram as we speak, and will remove the wire going into pin 2, showing that the shield only protects the wires themselves, but should not make an actual physical connection to the scanner amp itself.

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If it was really this the writer's intention, the diagram is very confused, and therefore it is wrong and it needs to be updated, please confirm with Thanos and inform any modification.

Quote:

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Also, I have taken another look at the picture of the printed wording from the Cambridge manual you have in your earlier post. This APPEARS to have some conflicting information, but it really doesn't. Unfortunately, the words on that page only make COMPLETE sense when they are interpreted in the context of another diagram in the Cambridge manual called "Power connections". This other diagram shows two separate, single-voltage, power supplies used, not one dual-voltage power supply as is commonly distributed with Chinese scanners. Cambridge chose to show a particular connection methodology whereby the two separate power supplies are connected to the two separate scanner amps, but I personally don't like that connection methodology very much, and it just about requires this separate heavy-gauge wire to be used.

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The Diagram "Power Connections" is below and this other diagram shows two separate, single-voltage, power supplies and this CT particular connection methodology with two separate power supplies is called "Bridge Connections", because the power supplies are connected in series, but it doesn't have any relation with the diagram " Signal Connections", however it recommends to connect heavy wire between both grounds to avoid strong coupling between channels caused by high ground currents to reduce the Crosstalk.
Do you think then should not have two separate power supplies and yes a dual-voltage power supply as is usually distributed with Chinese scanners?

Quote:

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Incidentally, the wire Cambridge discusses there really isn't related to this matter. It's there for power reasons, not for signal reasons. Nevertheless, we will see if Cambridge updates this document as well, to show that, for clarity purposes, the power supply connections could be made in a simpler way with ground connections meeting at the power supply, rather than using this separate heavy gauge wire.
Whew!! A lot of words for just one simple thing. Although this subject has been contentious and controversial (sheesh) I am glad that it has come up because it gives us a chance to review AND CORRECT our own documentation. (Thanks for pointing out these bugaboos DZ!)

---

I think really very important we seriously discuss this subject and other important ones and to contact the manufacturers to update the points discussed by the members of the PL Forum, logically when we arrived in a more appropriate conclusion and with the manufacturers' agreement.

Quote:

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And with all of this having been written, my recommendation stands. Don't connect anything to the "signal ground" of the scanner amps, and connect DB25 pin 25 only to some common, single point in the projector, preferably at the power supply.

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I will send shortly for your e-mail a Schematic Diagram with Input Power and Command Input Wiring (after I to draw) of my Micromax 671 series with 6215HB scanners for you to verify if it is everything correct the connections, OK?


Best Regards

Carlos

Hi Carlos,

You are confusing things a bit. Unfortunately, your confusion is exacerbated by the Cambridge diagrams...

And yes, it is Mike Thanos. I have known him for the past 20 years, and we have worked together on Cambridge-related projects. I don't need to "confirm" anything with him, because the facts are what they are. And any such further "confirmation" would only be a waste of everybody's time, and I am not interested in wasting their time. They are in the process of updating the "Signal connections" diagram as I already indicated, and once it is completed I will post it here.

For what it's worth, NC definitely means "no connection" or "not connected", and I am sure many others on PL will back me up on this one... If you don't believe me, look it up on the internet...

And yes, Mike is in full agreement with me. Only power connections should be "common" between scanner amps. The signals should be differential, just as I have been saying throughout this post. And no "signal ground" should be used.

This thick wire in the Cambridge diagrams is not something I like very much and I was amazed when I saw it in the diagram. At best, we can call it an "appendix". And we get a clue that this is an "appendix" by the fact that -- there is no real physical connector for it. On some boards you use a "spade lug", on others you solder a wire between this point and that point, etc.

You don't need the thick wire, if you simply "meet the power supply" at some central point, and then feed everything off of the centralized power supply connections. That's the cleanest and most understandable way to do. BUT, I admit that it does take more wire. The Cambridge method of tying power supplies directly to the amps basically requires less wire. Maybe that's why they did it that way. But there is no real central meeting place. The thick wire tries to create a happy medium, but... I just don't like it.

I won't forward Mike's email to you in its entirety -- not because I am ashamed of anything, but because I don't go forwarding the emails of others without their prior written permission willy-nilly. If you are interested, I will, however, forward the email I sent to Mike, so that you can see my points (all of which have been previously posted here), and see that I have not distored any facts. With my entire email and Mike's comment that "yes, Bill you are absolutely right on all points", hopefully that will give you a comfort level.

If you send me a diagram through email, I would be happy to give my comments, just as I am always happy to help out others here...

Nevertheless, all of this is really simple math guys... Only the power supply should be "common" among the scanner amps. On Chinese systems, this is natural, because they give you a single power supply that gives both voltages. Then you feed the scanner amp purely differentially (whether you are driving it that way or not) and connect DB25 pin 25 to the central grounding place, either on the power supply (in the case of a single power supply system) or at the power supply meeting place -- i.e. the central point. That's why it's called a STAR grounding schem, because all kinds of wires are meeting in a central point.

I do hope we can put this subject to bed now...

Bill

Quote:

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Originally Posted by Pangolin

I do hope we can put this subject to bed now...

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Ok, Bill we will put this subject now to bed, but it can be wakened up.....:D and as soon as I to draw the Diagram, I will send for you.

All the Best

Carlos