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Electronics LED's that fade OUT, not IN and OUT

Discussion in 'Modding' started by led_zeppelinzoso, 15 Feb 2007.

  1. led_zeppelinzoso

    led_zeppelinzoso New Member

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    I’ve been looking for a circuit for fading out LED’s and I’ve only been able to find ones that fade in and out, is there anything that will only fade them out? Would this work?

    [​IMG]
     
  2. cpemma

    cpemma Ecky thump

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    The capacitor needs to be across the power supply (after the switch) so turning the switch off leaves LED+resistor running from the cap charge.

    What exactly is the circuit the LED's with? If there are other ways for the cap to discharge on switch-off you may need a 1N4001 diode in the supply line.

    Code:
    +V ---->|---+---R---LED----+
                | +            |
               ===             |
                |              |
    0V ---------+--------------+
    
    Try 2000uF and adjust to suit.
     
  3. led_zeppelinzoso

    led_zeppelinzoso New Member

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    Its going to be about 35 to 40 led’s in parallel, so that’s close to 1 amp, I think. The switch is a pressure switch on a bass drum. So its only going to be a closed circuit for like 1/1000 of a second, and I don’t know if that’s a long enough time to charge the capacitor.

    I want it to work kinda like this. its for a slow part in a song were the bass drum is only hit every 3/4th of a second, and i want it to light up full brightness when its hit, but at the same time start to fade out and be off right before the next hit. I'm going to rig up a switch so I can switch through a few capacitors and change the fade time, and one that is just a flash, and one that is allways on.
     
  4. Soulmage

    Soulmage Member

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    If I am correct, you will want a circuit that works simaler to a flash. Have it powered and charged up so that when you hit the drum, it will already have the power stored up in both the "flash" cap and the discharge cap. How you would go about making such a circuit I do not know. Just the "idea".
     
  5. led_zeppelinzoso

    led_zeppelinzoso New Member

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    thats correct
     
  6. jakenbake

    jakenbake full duplex

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    maybe PWM will work...
     
  7. Hazer

    Hazer In time,you too will be relixalated

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    Cpemma's circuit will work just fine. You forget that when the switch gets 'closed', it will charge the capacitor almost instantly because it does not have a resistor limiting the current to charge it. But when the switch 'opens', the charge on the capacitor is slowly drained off because of the resistor in series with the LED. You will want to have individual capacitors for each LED though. It will be easier in the long run rather than getting expensive super capacitors that may or may not work the way you want. Just get one LED to work the way you want, and then copy the circuit 40 times. I would strongly suggest using the diode in the circuit though.
     
  8. ConKbot of Doom

    ConKbot of Doom New Member

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    I would use a 12v power supply/battery for all the LEDs and use a mosfet to fade off the LEDs with a circuit similar to the above ones hooked up to the gate of the mosfet.

    [​IMG]

    This would charge the cap and turn the mosfet on when you turn on the switch, as the variable resitor drains the cap, it would slowly turn off the mosfet too.

    Just make sure the mosfet can handle 12v on the gate, and 12v from the drain to source.

    A 10uf cap and a 50k variable resistor would take ~ 1.5s to discharge 95% of the way with the resistor turned all the way up.
     
  9. led_zeppelinzoso

    led_zeppelinzoso New Member

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    Thank you guys so much. But I need to ask one more thing. can somone tell me what capacitor(s) i need to use, and could I run maybe 4 or 5 leds off one of them insted of one off one. and what is a mosfet, and what kind do I need.
     
  10. ConKbot of Doom

    ConKbot of Doom New Member

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    A mosfet is a kind of transistor that is controlled by voltage instead of current,

    You could use pretty much any kind of N-channel mosfet, with a high enough voltage rating that it works with 12v...

    just a quick browse on www.mouser.com lead me to this,
    http://www.mouser.com/search/ProductDetail.aspx?R=FQPF13N06virtualkey51210000virtualkey512-FQPF13N06

    $.82 for one mosfet (get a few just in case...)

    you could get your other componets locally, though buying them from mouser would be cheaper.
    What sort of electronics stores do you have around you? Radio shack may or may not have mosfets, but online, they have the IRF510 for $2 which may be at your local store, or maybe not. It would work too.


    You should be able to locate all the components you need on mouser, LEDs might be a bit expensive from them, if you want cheap, check out ebay, and some of the LED suppliers from hong kong and other places.

    Also, I changed the circuit a bit,
    [​IMG]
    use 2 50k potentiometers and a 20uf capacitor. That would still give you a maximum fade time of 1.5 seconds or so, but the 2nd pot lets you adjust the voltage for the mosfet a bit.

    Mosfets decrease in resistance when you apply voltage to the gate pin, up until 9 to 11 volts for regular mosfets. If you are using a 12v supply and a mosfet that only needs up to 9v, applying 12v wont do any harm, but when it fades, it wont fade right away, there will be a pause, then start to fade. The potentiometer lets you compensate for this by lowering the voltage the gate gets.

    Mouser does ship to canada, so you can order from them if you want, or if you can, buy stuff locally.


    Though can I get one of the other electronics gurus here to double check my circuit and make sure I didn't make any silly mistakes?

    After you make the circuit, press the switch, turn up the 2nd pot and the lights should get brighter as you move the knob, after they stop getting brighter, you have the mosfet set right at the threshold. Then play with the first pot to adjust how fast it fades.
     
  11. cpemma

    cpemma Ecky thump

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    For many LEDs I'd use a power darlington source follower, the mosfet will have a very narrow voltage range over which it switches from full (1A) current to off.

    If the darlington has a gain of 1000 (TIP120) there's only 1mA drain max on the cap @ 1A load so a fairly small cap (20-100uF) will charge up PDQ but discharge slow enough. I assume you want it to fade out between beats, it's not exactly a long time.
     
    Last edited: 16 Feb 2007
  12. led_zeppelinzoso

    led_zeppelinzoso New Member

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    Yeah, and I want to be able to adjust the fade time, and have the ability to just have a pulse, y'know, for my double pedal :rock:
     
  13. ConKbot of Doom

    ConKbot of Doom New Member

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    yeah, I orginally designed it with a transistor, and then realized the transistor would be drawing more current then the drain resistor. But a darlington with low base current should work.
     
  14. led_zeppelinzoso

    led_zeppelinzoso New Member

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    I'm going to be useing 5mm UV LEDs, there about 3.2 - 3.4v, so I'm thinking of a source voltage of 12. That way I wont need resistors. so if you guys can give me a thumbs up on this and tell me what Petentiometers, capacitor, mosfet, and diod di I need.

    Is this a switch before the diod?
    [​IMG]

    Thank you guys so much!
     
    Last edited: 17 Feb 2007
  15. ConKbot of Doom

    ConKbot of Doom New Member

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    yeah, thats a switch, an if you put 4 in series giving them 3v each, they *should* be ok without resistors, as long as your supply voltage really remains at 12v and doesnt start to stray upwards.
     
  16. led_zeppelinzoso

    led_zeppelinzoso New Member

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    so its a switch from the + to the diod, right?

    an yeah, The suply voltage is from a 12v dc adapter, si it should all be good.

    what Petentiometers, capacitor, mosfet, and diod do I need? or that you would recomend?

    and why couldn't i build one that like, 5 sets of 4 (as shown in diagram as 3 sets of 3)
     
    Last edited: 17 Feb 2007
  17. scifi3018

    scifi3018 New Member

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    "2 50k potentiometers and a 20uf capacitor."
    A mosfet that can handle your max voltage
    and idk about the diode...
     
  18. jgrade

    jgrade New Member

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    I don't know about the electronics, I bow to the masters, but I do know about UV LEDs. If you intend to light a bass with UV LEDs to fluoresce a picture, etc then you may in for a rude surprise. UV LEDs produce little light, and less in the "UV" range. I have tried and been unsuccessful in most cases to get a result I like. I don't remember the wavelength of the LEDs I have (395nm I think) but they came from LS Diodes and were the brightest I could find. Since the upper limit of UVA is 400nm, these barely classify as UV and emit mostly visible light. Remember the shorter the wavelength the better.

    Good luck. Post a picture of the finished product.
     
  19. led_zeppelinzoso

    led_zeppelinzoso New Member

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    Dont wory man, its for a part in a song were we have the house lights turned off, so it should work fine, I hope. and were eventualy doing the whole kit, and even the cymbal's, from underneith.
     

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