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Small, bright, power-cheap lights

Discussion in 'Electronic Basics' started by [email protected], Apr 14, 2006.

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  1. Guest

    I'm trying to make a vibration triggered light which will need to be
    quite bright using, if possible, no mains connection so batteries only.
    I've been looking at LED's but im not sure how much light they produce,
    i've also looked at Luxeon lights but i have little idea wot im looking
    for.
    The light must be bright enough to fill a cylinder roughly 12x14 inches
    and produce a good glow.

    Any ideas would be much appreciated, bearing in mind i have little to
    none electronics know-how ;)

    Thanks

    Blue
     
  2. Chris

    Chris Guest

    Hi, Blue. As far as light selection, you'll have to make the call
    yourself. The "ultra-bright" white LEDs do provide quite a bit of
    light (they're garishly bright in comparison with standard LEDs), but
    they're usually somewhat directional. One of the really bright ones
    put out a good fraction of the light of one of those two AA battery
    "penlight" flashlight bulbs.

    If you do use ultra-bright white LEDs, you may want to get ones which
    are specified as "diffuse", or show a wide viewing angle. That will
    mean the light is spread over a wide angle instead of being focused by
    a lens at a small angle. But you didn't describe your application well
    enough to determine.

    Let's assume you're going to be working off 4 AA batteries, so you'll
    have 6V to play with. Each LED is going to require 20mA. You'll need
    a series resistor for each one. With a 6V supply, and assuming a
    forward voltage of 3.6V, that means you'll need a series resistor to
    limit current for each LED. Note that an LED is a diode, and will only
    work properly with current going in one direction. Solder your
    resistor to one lead of the LED (the long lead), and briefly hook it up
    to the 6V. If it doesn't light, it will work with the battery hooked
    up the other way.

    Now that you've got that end of it together, let's assume you're going
    to need 5 LEDs. That will mean a total of 100mA current from the 4 AA
    batteries. If you use alkaline batteries, that should mean 10 to 20
    hours on-time 'till the batteries are totally cashed.

    Now let's talk about the driving circuit. I'm going to assume you can
    get a normally-open tilt switch from one of those $4 pedometers they're
    selling at WalMart these days. Now ideally, you'd want a driving
    circuit that would use no current, to maximize your battery life.
    That's almost possible by using a small SCR which can be triggered by
    the tilt switch. The only time extra current is used is when the tilt
    switch is jiggled. When that happens, you'll have to turn off the
    power to get the SCR to turn off (you can put a pushbutton in your
    device if you wish).

    The difficulty is that about 1 or 1.2V will be dropped across the SCR
    when it's on. That will mean you'll only have 5V to play with, which
    means you'll have to reduce your resistor to 68 ohms. So your entire
    circuit would look something like this (view in fixed font or M$
    Notepad):

    | _/
    | .--o/ o-----o-----o---o---o---o---.
    | | SW2 | | | | | |
    | | (opt.) | | | | | |
    | | | .-. .-. .-. .-. .-.
    | | | | | | | | | | | | |5X68 ohm
    | +| | | | | | | | | | | |
    | --- .-. '-' '-' '-' '-' '-'
    | 6V - | | | | | | |5 White LEDs
    | | 220| | V~ V~ V~ V~ V~
    | | '-' -~ -~ -~ -~ -~
    | | | | | | | |
    | | | | | | |
    | | | '---o---o---o---o
    | | | |
    | | | V
    | | | _/ -
    | | '-----o/ o-------o--/|
    | | SW1 | |
    | | .-. |
    | | 10K| | |
    | | | | |
    | | '-' |
    | | | |
    | '------------------------------o---'
    |
    |
    (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

    You can use a 2N5061 SCR for this circuit. SW2 is the optional
    normally closed pushbutton you'll need to turn things off.

    If this is too complicated, if any of the above assumptions are wrong,
    if you have trouble finding parts, or if you have further questions,
    feel free to post again. You can also use a small reed relay to drive
    this, which will use 10mA more, but will be easier to put together.

    Good luck
    Chris
     
  3. Chris

    Chris Guest

    Hi, Blue. If you've got the time to scrounge for a part, you can get a
    5VDC 500 ohm coil DIP relay (like Jameco 138430CK, Clare p/n 2D1A05 for
    $2.29 ea.) and try this (view in fixed font or M$ Notepad):

    | _/ _/
    | .--o/ o--o---o/ o----o-----o---o---o---o---.
    | | SW2 | SW1 | | | | | |
    | | (opt.) | (tilt) | | | | | |
    | | | | .-. .-. .-. .-. .-.
    | | | || | | | | | | | | | | |5X120 ohm
    | | '-----||-----o | | | | | | | | | |
    | | || | '-' '-' '-' '-' '-'
    | | CRY1 | | | | | |5 White LEDs
    | | .-. V~ V~ V~ V~ V~
    | | 100| | -~ -~ -~ -~ -~
    | | | | | | | | |
    | | '-' | | | | |
    | | | '---o---o---o---o
    | |+ .----o |
    | --- | | |
    | - 6V | |RY1 |
    | | | C| |
    | | - C| |
    | | ^ C| |
    | | | | |
    | | | | |
    | '-----------------o----o---------------------'
    |
    (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

    Again, SW2 is the optional normally closed pushbutton. When the tilt
    switch turns on the relay coil, the contact bypasses the switch, making
    it latch in until you remove power, press the pushbutton, or the
    batteries die. The 100 ohm resistor in series with the coil keeps the
    coil voltage at 5V (and saves extra current). The relay specified has
    a diode built in (shown). If your reed relay doesn't, use any small
    signal diode.

    The problem, of course, is that you need 10mA extra to run the relay
    coil. If you wanted to get radical about this problem but still wanted
    the reliability and convenience of a relay, you might want to try a
    latching relay. But that's extra expense, and another story.

    Good luck
    Chris
     
  4. Guest

    Hey Chris, thanks for the reply!
    Sorry, i didnt explain myself very well so if i do so can you advise
    whether your solution would still be sufficient.

    I play the drums and get bored letting the guitarists/singer having all
    the fun! Therefore i wanted to create a lighting system where when i
    hit each individual drum a beam of (coloured) light would shoot from
    it. Well that was my idea, whether a 'beam of light' would be possible
    without spending a fortune im not sure.
    Essentially the size and power are the main issues. The bassdrum could
    hold the main powersupply with wires to the lights or something.
    Another problem would be to only get the single drum to light up when
    hit, as vibrations tend to pass through the whole kit.

    Thanks again for the reply, any new ideas would be very useful

    Blue
     
  5. Rich Grise

    Rich Grise Guest

    Google "contact microphone". Then, you'd have to do a little signal
    conditioning, like a threshold detector, and if you want to get really
    flashy, you could use that to trigger strobes from disposable cameras,
    with color filters. Or, as has been suggested, some super-bright LEDs -
    if the lights only flash on the beat, it shouldn't be too hard on the
    battery, and if you're putting that inside the BD, you could use a
    line-operated PS - you have to plug in all of your amps and other
    light stuff, why not plug in the bass?

    Good Luck!
    Rich
     
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