Modulation in BEYOND

[dnar]

I'd like to think my drivers clamp the mod input to 5v max for safety, but maybe I'm being optimistic...?

Yeah, but I found the FB3 wasn't driving the modules to 5V, more like 4.5 volts max.

[norty303]

Ah, so an impedance issue on the driver mod then?

[dnar]

Ah, so an impedance issue on the driver mod then?

I think so, either that or the FB3 can't drive outputs to 5V.

I previously measured modulation with static beams and only measured 4.5V on all heads.

[norty303]

I think so, either that or the FB3 can't drive outputs to 5V.

Ooh, this one again.... (My previous comment was a leading one....)

Bill got quite involved on a previous thread where 'FB3 low power' was discussed at length, it was quite a good read, and lots of options were covered.

[dnar]

Ooh, this one again.... (My previous comment was a leading one....)

Bill got quite involved on a previous thread where 'FB3 low power' was discussed at length, it was quite a good read, and lots of options were covered.

hehe. And that's what led to me fitting a DZ colour correction board!!!! It's a circular argument!

[White-Light]

There is a full set of ILDA test frames including some with fades in QS as standard.

Go to Settings > Projector Settings and the 1st ILDA Pattern is displayed under the Show it Now Window.

By clicking the slider bar underneath, you can change the type of test pattern displayed with every click.

The bar under that controls brightness should you need to adjust that to reduce reflection.




Are you impressed with the results of the board Dnar?

[DZ]

I think so, either that or the FB3 can't drive outputs to 5V.

I previously measured modulation with static beams and only measured 4.5V on all heads.

Ooh, this one again.... (My previous comment was a leading one....)

Bill got quite involved on a previous thread where 'FB3 low power' was discussed at length, it was quite a good read, and lots of options were covered.

Yeah, this was discussed at length on a number of occasions, ultimately, you can't really test the output with a voltmeter, an oscilloscope is required. I've never had the opportunity to put an o'scope on an FB3 to verify, though I'm sure it output correct. Even if it doesn't, as dnar indicated, yes the color board does have a gain stage. All of the op amp stages are unity with the exception to one. The gain will be either 1.1 or 1.3, depending on the resistor used. So, with a 5V input signal you could have a 6.5V output signal, right? Not exactly, as part of the protection stage the output of the color board is clamped to 5.1V (zener) on the + side, and if you inadvertently shifted the offset too far negative, instead of -5V to the laser driver, I think the max was around -.3 or -.4V. This is all true for the original color board, I have not seen Rob's version, yet. If he followed the schematic that I sent him then it will be identical. One of the test I performed with the prototype was to attach 110VAC to the color lines and the output never exceeded +5.1V, keeping the laser protected. I don't recommend trying this, but it has been done successfully.

Going back to the 4.5V issue on the modulation line from the FB3. Another point was brought up in previous discussions. There are some solid state laser drivers out there with very low impedance, I've seen less than 1K, but lets use 1K as an example. At 1K input impendance, you are pushing 5mA from your DAC to the solid state driver. Certainly not bad, the output of any tl084 can handle 5mA all day long. The reason you end up with 4.5V at the projector is because of the ~100 ohm of output impedance designed into the FB3 as well as the QM2K. That's where the .5V ends up going. 5mA * 100 ohm, .5V. Here's where the front end of the color board plays a big part, it has a very high input impedance, probably too high. High enough that it's prone to picking up noise. The good part, is that it is a differential receiver, so whatever noise is picked up by the ilda cable is mirrored on both the +color line and -color line (gnd) and ultimately discarded, passing thru a clean signal from the DAC to you laser driver.

[planters]

I have measured the output of the FB3 on an O-scope. Now, this is just one FB3 and there may be a variation unit to unit, but the voltage was spot on and was linear and accurate to the projector setup settings in BEYOND;60% output was 3.0 V. The impedance argument sounds about right.

[dnar]

There is a full set of ILDA test frames including some with fades in QS as standard.

Yes, I am aware of these.

Are you impressed with the results of the board Dnar?

Absolutely. My beam shows are more punchy. I am looking forward to tonight's show, it's using my full production with 3 projectors.

The good part, is that it is a differential receiver, so whatever noise is picked up by the ilda cable is mirrored on both the +color line and -color line (gnd) and ultimately discarded, passing thru a clean signal from the DAC to you laser driver.

AFAIC, the FB3 is not differential on the modulation signals, so a moot point.

High impedance inputs, connected to low impedance sources should keep the noise to a minimum anyways.