DMX control of laser intensity... help

[LASERGUY]

OK guys!

Here is another one of my electrical questions.


So I have one of these Logic Systems DMX0602A-DRV DMX decoder/driver boards..
8 channel output….

This control board consist of 6 HIGH CURRENT analog output channels (0-24volts)….
The remaining 2 channels can be toggled between PWM and 0-10 analog output.

My question today is I want to use the first 3 channels to control the intensity of my three laser systems (Analog inputs 0-5volts)…

Now I can easily just turn the pot on the control card to limit the voltage to 5 volts…
But the pots are very sensitive and I am afraid that they could drift or accidently spike to 24volts.

I attached a picture of a circuit I put together. I was going to make a voltage divider circuit. I was going to turn the pot all the way to max (24 volts) and rely on the divider to scale the voltage to 5 volts max.


To complicate things…. Each laser will receive two signals in the same input.
The analog control signal I send from the DMX card AND the signals from my ADAT or other control system.

The point is I want to have variable intensity control of the lasers when at my console.
When I am playing a show from ADAT I obviously would not be using my intensity sliders. But maybe I would want to bring up the green (Obviously this would override the modulation from the ADAT)

If you look at my attached circuit you can see a dedicated voltage divider for each laser.

I placed to diodes at the input of the laser to avoid cross talk from either source.

Any suggestions?
Any upgrades?

MOST IMPORTANT QUESTION!!!

These outputs are high current…. Up to 500mA!
What’s my situation with the laser inputs…. Will I fry the lasers?
My understanding is that the inputs to these lasers are high impedance....
Does this mean they will draw no current?

[Doc]

OK guys!


MOST IMPORTANT QUESTION!!!

These outputs are high current…. Up to 500mA!
What’s my situation with the laser inputs…. Will I fry the lasers?
My understanding is that the inputs to these lasers are high impedance....
Does this mean they will draw no current?

The high impedance will prevent them drawing high current, and a resitor divider network would be reliable with a regulated voltage, however; are you sure that the 24v is properly regulated? I'm sure somebody will chime in with a more robust regulated failsafe circuit.

[LASERGUY]

Doc,

Thanks for the reply..

I am not as worried aout the signal or intensity srifting slightly as much as I am abot damging the lasers.

Do you knoe what would happen of a Laser recieved the full 24 volts? :/

LG

[Doc]

It would more than likely kill the blanking circuit.

[Stuka]

Save the high-current outputs on your DMX0602A-DRV DMX for high-current requirements (actuators, etc.) and get one of these for your laser modulation:

http://home.att.net/~northlightsyste...512decoder.htm

The voltage outputs can be set for 5VDC - perfect for laser modulation!!

I've been using one for the modulation on my LaserWave 1 Watt 532 - works great!!

Regardless of what you use - adding a 5V zener diode across the modulation output can act as a "circuit breaker" in case the modulation voltage exceeds 5V.

[LASERGUY]

Stuka.... this page is awsome...

Are you talking about that $95 dollar jobber? =)
Thats pretty cool!!!

I may have some actuators in the main projector but I really wanted to save this Logicsystems card for maybe a beam table..

Thanks for the suggestion!!

BTW

The zener diode option... will the zener limit to 5 volts? Or will it trip and open the cuircut?

[Doc]

A zener diode would be wired across the supply after a current limiting resistor, any voltage above the diode threshold is short circuited.

[Stuka]

Stuka.... this page is awsome...

Are you talking about that $95 dollar jobber? =)
Thats pretty cool!!!

I may have some actuators in the main projector but I really wanted to save this Logicsystems card for maybe a beam table..

Thanks for the suggestion!!

BTW

The zener diode option... will the zener limit to 5 volts? Or will it trip and open the cuircut?

Yep, the cheapest one is all you'll need (just remember to configure it for 5V output!). It's got enough outputs for your RGB setup, plus 5 spares for the lasers you'll add later!

As Doc mentioned, the Zener diode acts like "safety fuse" to reroute excess voltage. This should NOT be your voltage regulator in and of itself, but could be used with other components as an added safety measure.

Even if you decide to use the 5V DMX decoder, you could still use Zener diodes on the 5V outputs as an added precaution. Not absolutely necessary, but wouldn't hurt, either...