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Thread: LED wiring in line-

  1. #1
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    Default LED wiring in line-

    may be a dumb question but-

    if wiring the shutter off of the pin 13 connection (or off of the 14, 17 pins for an interlock) is there enough juice to power a little led??

    what voltage is looped through the pin 13 (or 14, 17 loop) for the shutter? im assuming 5V?? and if so, if wiring the LED, it shouldnt drop enough voltage or current to disrupt the circuit to trip the shutter should it?

    -Marc

  2. #2
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    Most likely not (in regards to your last question, so yes it should probably work), it would really depend on your DAC. I was planning on doing something similar. If I get to it first I will let you know my results.

    I wanted to have a LED in parallel with the shutter to indicate Lasing. You would have to have a resistor to drop the current to the LED so it matches its specifications. But yes in theory it will work.

    If there is not enough current within the DAC's circuit, I would be surprised. But if that is the case a small Solid State Relay and another 5v regulated source would suffice. And I know there is plenty of 5v sources already cluttering my projector, with amperage to spare.
    Last edited by mliptack; 01-02-2008 at 18:00. Reason: clarification

  3. #3
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    FYI: You can get 5v TTL LEDs that have a resistor built in. It makes it a little easier for you.

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    Oh! Another option of course is to use the ILDA's "Intensity" output. Since most of us don't even use this control channel.

    I am not sure if the interlock control channel would work. I'll pull out my meter later and find out, unless someone knows how that particular circuit operates. I was under the impression that a loop was needed to be formed within that circuit for the projector to lase, however, I operate my projector and Interlock A & B are not looped together.

  5. #5
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    mliptack-

    good ideas! thanks! if you try any of these before i do, please let me know your outcome. and i will do the same.

    and im assuming that and LED will not drop anywhere near enough voltage or current to disrupt the loop circuit off pin 14, 17 or off of shutter pin 13.

    carmangary-

    yeah, gonna grab some of those lil 5V LED's from my work!

    thanks gentlemen!

    -Marc

  6. #6
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    Well I just purchased a pack of 100 LEDs 5000mcd for stocking up my electronics collection and doing exactly this! So I would say tomorrow night if not this weekend I will start experimenting (assuming the pack of LEDs gets here in time).

    -Max

  7. #7
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    Some years ago, I did mount a LED on my blanking signal, X, and Y signal to test the outputs togheter with the galvo conected

    And it did work with no problem !

  8. #8
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    Quote Originally Posted by mliptack View Post
    Oh! Another option of course is to use the ILDA's "Intensity" output. Since most of us don't even use this control channel.
    The intensity signal is not appropriate for a shutter or an emission indicator. The intensity signal goes low every time the laser blanks. This means your shutter would be trying to close every time the laser blanked (thousands of times per second), and then would need to open back up when the laser turned back on. It also means that your emission indicator would effectively be a strobe light.

    Your emission indicator should be tied to the shutter. Why? Because any time the shutter is open, you could potentially have output. Even if the laser is blanked, you sometimes have a little laser output anyway. (Some of the older Maxyz modules, for instance, would glow a dull red even with no power on the blanking line.) If the shutter is closed, you can't have any output.

    As to whether or not the shutter curcuit has enough power to run various devices, that's open to debate. It *should* have more than enough to drive an LED. It may *NOT* have enough to drive the LED and a shutter. That's why most people use a mosfet to actuate the shutter. And since you're already actuating a separate circuit, it makes sense to put the LED in that isolated circuit as well. But you don't have to.

    The interlock wires are designed to be in series with the rest of your projector safety circuit. Remember that the interlock pins are connected to each other at the controller end. There are no signals on those pins. The idea is that if the ILDA cable becomes unplugged, it interrupts the interlock circuit and shuts down the projector. (Yeah, I know, if the cable comes completely unplugged the shutter will close by itself because the shutter signal is gone, but this goes one step further and shuts everything off.)

    Think of the interlock pins as a loop of wire between the projector and the controller. Put that loop in series with your safety circuit for main power (your case-intrusion switches, your big red "stop" button, your keyswitch, and large relay that switches your main power to the projector) and it will work as intended.

    On the other hand, if you leave the interlock pins disconnected from everything, it will work just fine like that too. (But you won't have full safety protection.)

    Adam

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    Adam,

    Just to clarify what I meant. For some reason, I don't really know why besides the fact that it adds another LED that blinks, I plan on having 3 LEDs. One for power indication, one for Laser Emission and one for Laser On.

    The LED for power will be tied into the mains wiring... somehow.
    The LED for Laser Emission would be tied into the shutter (either I typed something weird or you misread my post - I never meant to say put the shutter onto the intensity channel. Since that would actually Blank the output every time the laser should emit)
    Finally the Laser On light... it will be a indicator strobe light, a strobe that will likely blink way too fast to notice (since 30hz is not noticeable).

    Another option for an LED that I am considering is an LED on a timing circuit that would blink when power is interrupted - In the case of an interlock being thrown. Or when the projector has power but the key switch has not been turned on yet. I am not quite sure how I am going to wire that one up yet, however.

    Adam thanks for clarifying the interlock A & B! It make sense now. Since its not hard to add that into my interlock circuit I will have to do that!

    Could you do one thing and clarify the mosfet in the shutter circuit? I bought some actuators that should be able to hold open on 3v, so I figure the shutter channel would be able to hold it. With an LED or not. But it would be nice to have that breathing room available

    -Max

  10. #10
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    The problem with driving the actuator directly off the shutter signal is that you're relying on the DAC being able to supply enough *current* to run the actuator. That's not really what they're designed for, and depending on the actuator you use, you may run into problems. Now, if you're using something like a GM-20, which has a separate power input apart from the switching signal, then you're OK. But if you're using something like a rotary solenoid, the DAC probably won't be able to drive it.

    In that case, it's better to use a mosfet as a voltage-activated switch. (Remember that Mosfets don't pull any current through the gate.) You simply run 5 volt power to the source lead on an N-channel mosfet and then connect the drain lead to your actuator. (Connect the other lead on the actuator to ground.) Now connect pin 13 (shutter) to the gate of the mosfet. When the shutter signal goes high (5 volts) the mosfet will turn on, which will power the actuator and open the shutter.

    As for the LED being wired to the intensity line - I suppose you could do that if you wanted, but it would be pretty pointless. The LED would be flashing very fast, and given the lower duty cycle (depending on how many blanked points you had) and the persistence of our vision, it will probably just look like a dim LED. But you can certainly hook it up without harming anything.

    Adam

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