How do I create this theatre lighting effect with LEDs?

Discussion in 'The Projects Forum' started by MeganL, Jun 13, 2018.

  1. MeganL

    Thread Starter New Member

    Jun 13, 2018
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    Hi,

    I’m directing a play for my local community theatre group, where I’m usually the lighting and sound tech. I’ve an idea for a particular effect, but I’m not sure how to put it together.

    I’ve attached a quick sketch below, but essentially I want to suspend 7 single LEDs over the stage, to create ‘stars’. Each one needs to be switched on individually, but then turned off together, from the tech booth, which is above and to the right of the stage. I have a basic electronics knowledge, but I’m not sure what I’ll need to do to make this work. I thought I could maybe cannibalise a battery powered led light string to get the LEDs, but that’s about as far as I’ve gotten.

    Any asssistance would be welcome.
    Thanks
     
  2. dl324

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    Mar 30, 2015
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    Welcome to AAC!

    You could wire the switches that control individual LEDS to a power rail that's switched. Opening the latter would remove power from any LEDS that were switched on.
     
  3. Bernard

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    Might be helpful for parts location if we knew what part of the world you live.
    For wide viewing angle might check automotive LED bulbs ?
     
  4. wayneh

    Expert

    Sep 9, 2010
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    The good news is that what you want is simple from the electric point of view. The bigger problem is choosing the LEDs, their color, brightness and diffuser arrangement, and arranging a power source. Have you chosen switches yet? Will the turn-on sequence be done by a human?
     
  5. MeganL

    Thread Starter New Member

    Jun 13, 2018
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    Thanks for the welcome. Yes, that makes sense to me. Although I’m not sure how to get the power from the master switch to the individual switches.

    Ah yes, sorry, I’m in the UK.

    I like the good news! My original plan was to take apart a simple battery powered string of LEDs, I’m happy with the colour and brightness that these provide. I need a cold, single point of light, in 7 places. It’s a very small theatre, and It’ll be mostly in blackout at this point, so they won’t be fighting other light.

    I’ve not chosen switches, or cable, or anything more than the original idea. I figure the battery pack (usually two AAs will be sufficient power, as it can handle 50 LEDs and I only need 7. Any advice in this area would be extremely welcome. I’m more used to dealing with 1kw lamps!

    Yes, I have a willing human to operate the switch on and off.
     
  6. dl324

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    upload_2018-6-14_7-5-13.png
    Switches are SPDT, all shows in the off position; you can use a switch of your choice (e.g. SPST). To start your LED sequencing, close SW8. Then close the switches for LEDs in whatever order you desire. When you want to turn all of them off, open SW8. Then you need to open the other switches before starting over.

    You could make it more convenient to operate by using momentary switches, but you'd have to add some circuitry.
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If 2 AA cells are powering a string of 50 LEDs then I assume the cells drive a DC boost circuit to create a higher voltage for the string. You would need an alternative supply for powering 7 LEDs individually.
     
  8. MeganL

    Thread Starter New Member

    Jun 13, 2018
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    This is great thanks! That makes sense me. A couple of questions; once the power leaves SW8, I wire to Sw1, is it sufficient to then wire straight to the next switch? Also, are you able to say what type of cable I should use?

    I don’t know, it’s just one of those cheap strings of fairy lights you can get. Looks to me like just a simple circuit, but I could be wrong.
     
  9. dl324

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    Do you mean the way I wired S1-7 to S8? If so, yes.
    You can use any wire/cable rated for the voltage and current you need.
    Another member was talking about cutting up those strings and reconnecting in other configurations. At minimum, they're simply surface mount LEDs in a plastic blob. Hopefully they have current limiting resistors in the blob, but my guess is that they don't. It's common for commercial things powered by 2 or 3 1.5V batteries to forego the resistors. They don't care if the LEDs burn out because you'll just buy another.

    Reputable designers would balk at doing something considered bad design practice. But the almighty penny speaks loudly to manufacturers who can save a few cents on a million widgets. It adds up. They're not after building a reputation. It's all about the money.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    If you mean in series, no. All 7 switches are in parallel with each other, but in series with the main SW8. Keep looking at the diagram if that's not clear. The setting of any of S1-7 has no bearing on the others. But S8 controls them all.

    The wire you choose is not important electrically - just about anything will work. Choose based on appearance or mechanical properties. Note that each LED will require two conductors all the way back to the switch box. You could run all the grounds together and not have all come back to the box, but I think that would actually be more confusing. You might want different colored wires for each LED so you can keep them straight, if that matters.
    There's almost certainly a boost converter in it, similar to a solar landscape light. You might get that to work for you but frankly I think the diagram is a better approach. You could use a 5V USB power supply, a 9V battery, maybe even a pack with 3 or 4 AAs. The resistors you use will depend on the voltage of your supply. The resistors could be soldered directly to the switches and all mounted on a project box.
     
  11. dl324

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    Here's a version of the circuit that doesn't require opening switches to reset. It uses momentary pushbutton switches:
    upload_2018-6-14_10-32-47.png
    I only showed 4, but you just replicate for as many as you want. You could use RS flip flops which come 4 in a package vs 2 for the D flip flops. I didn't use them because the symbol in my schematic editor doesn't show functionality as clearly.

    The RL*/LED* pairs represent your "stars". You'd route two wires from the power supply and the collector of the transistor to each of them. The circuit as drawn will barely provide a current of 10mA. If you need more, you'd need to use a darlington transistor for more current gain. If you're operating from a low voltage, you'd probably be better off with a split darlington configuration because it would give you another 0.7V across the LED.

    The rest of the logic and wiring would be on a main control board. Switch 8 is a main reset, but doesn't switch power as in the earlier circuit. When the circuit powers up, state of the LEDs isn't guaranteed and you'd use the reset switch to reset them. Then you use S1-7 to turn on LEDs in your desired sequence. When finished, push S8 to reset them.
     
  12. Bernard

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    One source in UK- London, is Mouser Electronics Some parts to look at:
    SPST SW, PN: 108-MS550K, @ L 2.04 or PN: 108-0001-EVX, @ L 2.48
    Battery box, 3 AA, PN: 534-2487
    Battery box, 3 C cell, PN: 12BH231-GR, @ L 1.61
    White, 5mm, 720-21000 mcd, LED. PN: 859-LTW-2S3D6 @ L .443
    Wire, 400 ft. 24 ga. hook up wire. PN: 566-8052, @ L 50.29. This needs more looking ?
     
  13. Bernard

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    'Forgot the resistors, 82 ohms, 1/4 W, carbon film, 5%., based on 4.5V supply & white LED.
     
  14. dl324

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    Here's the same circuit as above using RS flip flops:
    upload_2018-6-14_13-29-37.png
     
  15. wayneh

    Expert

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    Your circuit baffles me. Why would you use an IC to turn on an LED when you already have a manual switch?
     
  16. dl324

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    As I said to the OP. If having to open all of the switches for individual LEDs after turning them on is too inconvenient, adding circuitry can eliminate that inconvenience.

    The second and third circuits I posted do that. Any combination of LEDs can be turned on via momentary pushbutton switches. When they need to be reset, it can be done with a single switch.
     
  17. KJ6EAD

    Senior Member

    Apr 30, 2011
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    It's the lord of the switches.

    One switch to rule them all
    and in the darkness blind them.
     
    Last edited: Jun 14, 2018
    ebeowulf17 likes this.
  18. MeganL

    Thread Starter New Member

    Jun 13, 2018
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    I’m overwhelmed with how kind you’ve been in helping out. Thank you. I think I’m going to go with the original option. Seems within my capabilities. I’ll keep you posted on how it turns out, and if I need any more help
     
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