pots for colour balance mod

[badger1666]

hi
doing a rebuild of my projector now i have ordered a blue
i want to add three pots to adjust rgb colour balance
will three 10k pots put on the rgb blanking inputs work ok
also i want to add a laser test switch to turn on all lasers at full power
would it be ok to just take 5v from one of the laser power supplys
via a switch to the lasers or do i need some sort of current limiting
as well (i dont know if its safe to put a 5v 5amp supply on to a laser blanking input ??)

[buffo]

The 10K pot will work just fine. And yes, it's safe to connect the output of the 5 V PSU for the laser to the blanking lead to get it to run at 100% power. That's usually the way they ship from the factory.

The amperage capacity of the power source is irrelevant. The blanking line is a high-impedance input. It's designed to see zero to 5 volts. It doesn't matter if you connect a 100 milliamp PSU to that blanking line or a 100 amp PSU to it. So long as they are both putting out 5 volts, the blanking circuit will draw the same amount of current. The resistance of the blanking circuit determines the current draw, not the capacity of the PSU. (And most modulation inputs only draw a few milliamps.)

Adam

[The_Doctor]

That's true (though likely microamps), but on the other hand, it means you could run it through a 1K resistor and the correct effect will be the same. And a 1K resistor also won't overload the source if for any reason the signal line gets grounded or connects elsewhere in the laser system. I've found bits of solder stuck to a laser PSU board, even floating loose in there. So fitting the 1K resistor is damn good insurance for the money. You might see errant performance if things go wrong with the laser driver, but no worse unless the PSU itself is fatally flawed. With the 1K in series with its input you're never going to see meltdown or magic smoke as a result of your input.

[sbk]

You can make even better, an op-amp based circuit to set gain / offset, that will improve even more your color balance

Like the one on the Pangolin page : http://www.pangolin.com/resguide03d.htm

[The_Doctor]

I deliberately didn't mention that... Best to use nothing more complex than needed. In that light, there's this:
http://www.photonlexicon.com/forums/...5431#post75431
It's about as simple and adaptable as you can get if all you want is scale and offset. Most other designs are more restrictive of signal and PSU conditions. Either that, or more complex.

[stanwax]

You can make even better, an op-amp based circuit to set gain / offset, that will improve even more your color balance

Like the one on the Pangolin page : http://www.pangolin.com/resguide03d.htm

As I am developing at present with some other goodies. See pic of colour smoothing and safety interlock prototype. Currently has Ilda in/out, colour smoothing, 12V outputs for fan power, connection for a keyswitch plus relay for turning laser power on and off as part of the safety intelock plus an interlock startup timer. 9 pin connector is for output to e-stop m(this will also carry connections for laser start/reset function if needed)
There are a couple of other 'modules' planned to be added and once its developed it will be redesigned on the same PCB size (aprox 170x60mm - certainly no bigger) in SMD
A free finished board to the first person who spots the error on this board

Rob

[p1t8ull]

25 way D-Sub is the wrong way round?

[stanwax]

Bloody hell
hawkeye - you win!



Rob

[p1t8ull]

Wahooo!!

If it was an electromagical issue it would've been a very different outcome indeed

Nice lookin' board Rob, very pro

[stanwax]

well strictly is an electromagical issue - for theose who dont understand placing 2 25ways next to each other and wiring 1 to 1 as the board shows with the straight trax would mean ilda in pin 1 connects to ilda out 13 - not good!

Nice lookin' board Rob, very pro

Cheers m8 not too bad since its knocked up in my garage - will be even better when I make the next one as I just made a 'viewer' to assist in accurate drilling of pcb holes with my dremmel using a vid camera 2 bits of old worktop and an old scrap portable dvd player

Rob