So what does Analogue Modulation do exactly?

[VW]

I tried googling the subject, but the info is a quite vast and rigerous to get through. I was wondering, what is it that analogue modulation actually does to help get a good mix of colours with an RGB set up? Obviously it must change some properties with the beam, but I'm lost as to what that is. Any info is appreciated...

 

[Murudai]

Two main kinds of modulation. TTL and analogue.

TTL just switches the laser on and off. Analogue on the other hand allows the power of the beam to be carefully adjusted. TTL can just be no power or full power, where as analogue can be any power between none and full.

TTL is alright for single colour projectors, but for multi colour projectors you need analgoue to get a perfect colour balance. For example if in you projector setup your green is too powerful and it's making your colours too 'green' with analogue you can reduce the output to the right levels.

It also means you can produce a full colour spectrum, any colour you want That's what I want with my RGB scanner I want to build

 

[pseudonomen137]

They are both ways to control your lasers output with an input signal (IE, if you need to control output via a computer or in any case where its important to change output remotely and/or quickly)

TTL is a digital method - like a computer you have 0's and 1's. Either its 0V for laser off or +5V for laser on, or vice versa.

Analog(ue) is 0-5V and everything in between. It gives you a continuous range to input and output *should* linearly follow the input (a completely linear relationship is the ideal case, but the less you pay, the further it'll likely be from linear)

TTL speeds are typically faster and it has its whole range of uses. As Murudai says though, analog(ue) is ideal for lasershow projectors. Imagine an RGB. With TTL you can have red, green, blue and composites of R+G=yellow, R+B=purple, G+B=cyan, R+G+B=white for a total of 7 colors. Pretty impressive and actually by using TTL at very fast rates you can simulate more colors (imagine flipping a color on/off 30,000 times a second - it'd simulate running it at half power). However for real lasershow systems where you want the full gamut of RGB and all its composites, you need analog modulation.

 

[VW]

Thanks, I get the idea now.  So, for example, modulation comes in different percentages right?  Like 3%, 5%, 10% and so forth.  What are they?  Are they the accuracy at which you can stabalise the power level?  Like Murudai, I plan to construct an RGB scanner in the future and money is of great issue.  I've seen ones at laser glow which go up to like, $4000 just for 100mW at 3%, way too pricey for my liking.  Does the percentage not make too much difference?  Or is this a point where money really does buy you value?  473nm has to be my first choice as getting the big one out of the way, while I still mess around with time machines, spirographs, XY scanners and may 20K scanners with my current lasers makes perfect sense.  But yeah, understanding what I'm aiming for is crucial... $2000 would be my absolute MAX for 473nm... Would you still be able to construct a good set up on that kind of budget at 10%? (Assuming both G and R are suitable matches)

 

[Murudai]

Hey, I've got a question I'd like to throw out there.

I see lab lasers and stuff that talk about '10kHz modulation' or '20kHz modulation'. So that's 10,000 and 20,000 per second. But scanners can be 20kpps and up to 40kpps. That's 20,000 and 40,000! What happens when the scanner is going faster than the laser can do modulation? Do you have to buy lasers which can match your scanner rate?


As for your question VW. I'm not sure what you mean, analogue doesn't come in percentages. I think you're talking about power stability, and how stable the output of the laser is. For a laser show, this isn't really an issue. Obviously greater stability means you can get a more accurate colour balance, but you wouldn't notice the difference really.

 

[diachi]

KHz and Kpps is different, 20Kpps is 20,000 points per second, meaning if you have your scanners running at 20Kpps there are as much as 20,000 points displayed every second, this doesnt exactly mean the laser must modulate at 20KHz, the laser only needs to be switched on or off when theres a gap in the graphic, so you dont get all the bits of the graphic joined together in one bg long line .

 

[diachi]

Ok, so say this is your image, right?, and this image is displayed at a rate of 60FPS, the galvos (running at 20Kpps) would just spin to creat a single line, but the laser would be modulated so that it turns on then off then on 60 times a second ( how many times would it turn off a second then ? 20, or 180 ? ) anyway it goes through the cycle of on off on 60 times a second, which I believe to be 60Hz modulation. ( could be 20 or 180 though  ;D ) hopefully you get the idea

basically what im trying to say is that you can run 40Kpps scanners with 10Khz modulation, but the modulation rate has not much to do with the scanners, but more the graphics being displayed .

 

[Murudai]

Yeah, that's what I was thinking. But what about analogue? What if you want, say, a colour gradient or something? Wouldn't that kind of mess things up?

Though... I suppose you wouldn't normally do something like that... so I guess it wouldn't be too much of a problem...

 

[FrothyChimp]

Thanks, I get the idea now.  So, for example, modulation comes in different percentages right?  Like 3%, 5%, 10% and so forth.  What are they?  

The percentages you are discussing are power stability rating. The percentage indicates the variability in the output power when it is at operating temperature. If you need exactly 100mW all the time you would want a stability that was very low (<1%) but for light shows you get a margin you can work with. I've seen shows use 10% stability and it works fine. The only time it would affect a laser show would be when you are creating specific colors with combinations of beams. If a green was to output 10% more power and a red happened to output 10% less power when combining the beams the color you would get would not be exactly what you were looking for but since it is a probability issue the color would change a bit as the outputs change but ever so slightly. Things are moving so fast during a light show it may not be much of an issue. Improving output stability is primarily a result of improving the electrical stability of the pump driver. Hence, the better the stability the higher the cost.

 

[diachi]

Yeah, that's what I was thinking. But what about analogue? What if you want, say, a colour gradient or something? Wouldn't that kind of mess things up?

Though... I suppose you wouldn't normally do something like that... so I guess it wouldn't be too much of a problem...

Analogue is for mixing colours at different levels, so you can get different 'shades' of colours, without analogue you would be limited to 7 colours, but with it you can get any colour in the rainbow ( if your using RGB ) with TTL modulation 0V is on 5V is off, or vice versa, you cant get in between its either 1 or 0, on or off, with analogue 0V is on and 5V is off, or vice versa, but 2.5V would be roughly half power, so you can get on or off, or all the stages in between .

Best way to describe it is like two light switches, one just switches on or off, the other is a dimmer switch, it can make the light any brightness between off and full power.

 

[Murudai]

[quote author=Murudai link=1218901355/0#7 date=1218930915]Yeah, that's what I was thinking. But what about analogue? What if you want, say, a colour gradient or something? Wouldn't that kind of mess things up?

Though... I suppose you wouldn't normally do something like that... so I guess it wouldn't be too much of a problem...

Analogue is for mixing colours at different levels, so you can get different 'shades' of colours, without analogue you would be limited to 7 colours, but with it you can get any colour in the rainbow ( if your using RGB ) with TTL modulation 0V is on 5V is off, or vice versa, you cant get in between its either 1 or 0, on or off, with analogue 0V is on and 5V is off, or vice versa, but 2.5V would be roughly half power, so you can get on or off, or all the stages in between .

Best way to describe it is like two light switches, one just switches on or off, the other is a dimmer switch, it can make the light any brightness between off and full power.[/quote]

wtf are you crapping on about. I KNOW what analogue is, if you look in the FIRST reply in this thread, you'll see where I said the SAME thing as you just said to answer the original question in this thread.

you fail at reading


Let me make it clearer then. Say you want a colour gradient, you want to slowly go from green to blue lets say over a second, with all the colours in between. And you want to scan across the room. The scanner will scan across at 20,000, but the analogue modulation only works at 10,000. Does that mean that it will just gradient every second point in the scan? Or will it screw up completely, because you're pushing it too hard?

 

[VW]

I see, thanks.

 

[diachi]

[quote author=Diachi link=1218901355/0#9 date=1218936626][quote author=Murudai link=1218901355/0#7 date=1218930915]Yeah, that's what I was thinking. But what about analogue? What if you want, say, a colour gradient or something? Wouldn't that kind of mess things up?

Though... I suppose you wouldn't normally do something like that... so I guess it wouldn't be too much of a problem...

Analogue is for mixing colours at different levels, so you can get different 'shades' of colours, without analogue you would be limited to 7 colours, but with it you can get any colour in the rainbow ( if your using RGB ) with TTL modulation 0V is on 5V is off, or vice versa, you cant get in between its either 1 or 0, on or off, with analogue 0V is on and 5V is off, or vice versa, but 2.5V would be roughly half power, so you can get on or off, or all the stages in between .

Best way to describe it is like two light switches, one just switches on or off, the other is a dimmer switch, it can make the light any brightness between off and full power.[/quote]

wtf are you crapping on about. I KNOW what analogue is, if you look in the FIRST reply in this thread, you'll see where I said the SAME thing as you just said to answer the original question in this thread.

you fail at reading  


Let me make it clearer then. Say you want a colour gradient, you want to slowly go from green to blue lets say over a second, with all the colours in between. And you want to scan across the room. The scanner will scan across at 20,000, but the analogue modulation only works at 10,000. Does that mean that it will just gradient every second point in the scan? Or will it screw up completely, because you're pushing it too hard?[/quote]


Hey!!! that was uncalled for, bringing my bad reading skills into it like that !!

But anyway, I'm not sure about that, I'm guessing your right though.

 

[pseudonomen137]

[quote author=VW link=1218901355/0#3 date=1218911941]Thanks, I get the idea now.  So, for example, modulation comes in different percentages right?  Like 3%, 5%, 10% and so forth.  What are they?  

The percentages you are discussing are power stability rating. The percentage indicates the variability in the output power when it is at operating temperature. If you need exactly 100mW all the time you would want a stability that was very low (<1%) but for light shows you get a margin you can work with. I've seen shows use 10% stability and it works fine. The only time it would affect a laser show would be when you are creating specific colors with combinations of beams. If a green was to output 10% more power and a red happened to output 10% less power when combining the beams the color you would get would not be exactly what you were looking for but since it is a probability issue the color would change a bit as the outputs change but ever so slightly. Things are moving so fast during a light show it may not be much of an issue. Improving output stability is primarily a result of improving the electrical stability of the pump driver. Hence, the better the stability the higher the cost.
[/quote]

^ When you're through with the bickering, make sure you guys read that (the percentage has nothing to do with the modulation - even lasers without modulation may be rated to certain stability tolerances)

 

[thesk8nmidget]

TTL

analogue