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Thread: flashing LED voltage question

  1. #1
    daz
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    flashing LED voltage question

    It's rated 3-5vdc. Says it'll flash 150 times/min at 3 v. Will it flash faster at higher vdc and is there any way to determine how much more at any given voltage?

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    Old Timer Tom Phillips's Avatar
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    An LED just turns on when it receives the proper voltage and off when the voltage is turned off. If you have a flashing LED then there is a circuit controlling the flashing. We need to see the whole circuit to be able to answer your question.

  3. #3
    daz
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    Are you saying there are no LED's that flash without a circuit? I'm looking at a page of LEDs at this place in the link below and there are all sorts of LED's including "flashing" LED's. Does this mean regular LEDs in a flashing circuit will not flash? But if they do, then why are there flashing LEDs available and regular LEDs? Whats the difference?

    LEDs | All Electronics Corp.

  4. #4
    daz
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    Ok, just found one that describes in detail that it doesn't need anything but a power source. So there ARE self flashing LED's that don't need a circuit as i already expected when i was going to buy the one at allelectronics. You had me worried ! Heres what it says in an ebay ad i found...


    Now in one of the most popular sizes, we have brought a flashing led. The 3mm flashing round top cool / clear white led will automatically start flashing once it is appropriately hooked up to power. There is nothing extra needed when hooking this led up to power. A power source, led, and resistor is all you need.

    We use and have only the highest quality leds out there.
    Now if anyone knows the answer to my original question, please have at it.

  5. #5
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    The LED that you are looking at has a built-in chip that flashes the light, so no outside circuit is needed. I have used them for fun projects, but I never was concerned about the flash rate.

    What are you trying to do with the flashing LED?

  6. #6
    daz
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    Well, it's a very long story. Digital modeling amp by the way. I'll try and make it concise as possible. I put the guts of an expression pedal in my pedalboard. I only use it to get a 10% volume boost so i don't want a bulky pedal to carry around and i want a single button to hit and get about a 10% volume boost. So at the amp i program it;s volume mode to have a 10% volume reduction in volume mode. Then when you hit the pedal's switch, which is now mounted in my pedalboard along with the guts, it switches between volume mode and exp mode. I have both heel and toe volume levels set to 90% and exp mode set to "off". So when i hit the button it should go from volume mode's 90% volume (90% of wherever the amp's master is set) to completely off and 100% volume. So now i have a single footswitch that gets me a 10% volume boost. (or any % i want it to be)

    This is where the flasher comes in. I found that it doesn't work reliably because the sensor needs to be stimulated with some sort of light or movement. In the pedal it see the movement of a little thing that moves in front of the sensor with the movement of the pedal. So it works, but it's intermittent. Sometimes it doesn't change the volume, sometimes a delay of up to 10 seconds before it changes, etc etc. So i tried waving a finger back and fourth in front of the sensor while switching it and that worked. then i tried a flashing LED on my footswitch that flashes to show you the delay.s time. It worked too but somewhat less reliably. But it's not bright at all and green. So if i mount this bright white one in front of the sensor it should work much better and i can power it with the pedals 3.5v. But i posted this because the faster it flashes the more reliably it is as i found by testing it with that delay;s LED and finger movement. The faster the better. So if it's not reliable i could power it some other way. Hope not to have to but if it's not reliable enough as is i'd be willing to use my tube screamer's supply and drop it to the necassary voltage.

    Well, so much for concise !

  7. #7
    daz
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    Got em, tried it, works good.....well one does. I bought 3 types hoping one would be good. One doesn't work because when i attach it to the 3v it kills the footswitch and it doesn't light up. The FS's LCD and LCD's go out and it becomes non operational. Another lights up and the footswitch works but it doesn't flash. It flashed in the store connected to a 3v wafer battery. The last one works. Flashes and the FS works. Good thing i decided to try several types ! I just had a gut feeling that the one i went there to get somehow might not work even tho they let me test them all with a battery. So i tried 3 types and luckily one worked. What would it be about the control voltage to the switch that would cause the issue with the first 2? Were they just pulling too much current?

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    rjb
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    The All-Electronics listings I found all say that the LED contains a built-in flashing unit- but not much else.
    I found no listing that mentioned 150 flashes/minute.
    Flashing | All Electronics Corp.

    But I did find this data sheet for a self-flashing LED. It appears that the flash rate decreases as forward voltage & current are increased. However, I don't know if different manufacturers use different flashing unit designs.
    http://www.lumex.com/content/files/P...LX5093BSRD.pdf
    BLINKING FREQUENCY:
    1.5 Hz typ (90 flashes/min) @ Vf = 14.0, If = 44 mA
    3 Hz typ (180 flashes/min) @ Vf = 3.3, If = 8 mA

    -rb

    EDIT
    Oops, daz posted while I was called away in the middle of typing this.

  9. #9
    rjb
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    Quote Originally Posted by daz View Post
    What would it be about the control voltage to the switch that would cause the issue with the first 2? Were they just pulling too much current?
    Probably even with the flashing unit, you should still treat the LEDs as forward-biased diodes. That is, you have to know what forward current (& corresponding forward voltage) you want, and provide an in-line resistor from your power supply to drop voltage and limit current. But I am just guessing.

    -rb

  10. #10
    daz
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    Quote Originally Posted by rjb View Post
    The All-Electronics listings I found all say that the LED contains a built-in flashing unit- but not much else.
    I found no listing that mentioned 150 flashes/minute.
    It's here... WHITE FLASHING LED, 5MM | All Electronics Corp.

  11. #11
    rjb
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    Quote Originally Posted by daz View Post
    OK, I see it has the flash rate at 3V. My bad. But it still doesn't list important specs like maximum forward current.

    -rb

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