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Piddling around with more LEDs

Discussion in 'Electronic Design' started by Tim Williams, Dec 25, 2008.

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  1. Tim Williams

    Tim Williams Guest

    80 LEDs (so far; I'm going to whip up another string of 40 yet), a PWM
    driver (LM393) and an isolated switch running strings off the line.



    Tim
     
  2. neon

    neon

    1,325
    0
    Oct 21, 2006
    use a triac direct from the line how many on a string? use a diode and a big cap 84 LED . not only that no PWM just direct from my HI-FI output beat that if you can? want to know more?
     
    Last edited: Dec 25, 2008
  3. Tim Williams

    Tim Williams Guest

    Usually done by blending together (AND, OR, XOR?) three squarewave
    oscillators running at different frequencies. I don't like the results
    though. Is there a strong source of slow (1/f) noise? Maybe FET CCS
    amplified a bunch?

    Ironically, this controller flickers pretty well at low bias. I'm guessing
    ambient noise is enough to push it just over threshold, since there is some
    hysteresis between "fully off" and "lowest duty cycle". It doesn't hurt
    that vision is logarithmic so you can clearly see microamperes in the damn
    LEDs (I can't probe the switch's drain waveform without the LEDs glowing a
    little, and it's a 10M probe). I haven't decided yet if it's noise in the
    "differential" amplifier (= two transistors and two resistors, bad CMRR,
    etc.), jitter in the PWM comparator, line noise or what.

    Tim
     
  4. krw

    krw Guest

    I bought 1000 LEDs for the outside this year. Ick! What horrible
    light. I've already bought incandescents to replace them for next
    year. The LED strings go in the garbage as soon as the holidays
    are over. A waste of $150, but sometimes education costs.
     
  5. krw

    krw Guest


    These are bluish-white and the flicker is horrible. They're built
    like crap too, but that's another issue.
     
  6. Tim Williams

    Tim Williams Guest

    Easy to "rectify" anyway... cut off the ends and have at it.

    Tim
     
  7. krw

    krw Guest

    They're called "cool white", but they're sickly blue.
    60Hz. Many can't see 60Hz flicker (evidenced by their monitor
    setups). I can.
    Cheap? No, over 10x the price of incandescents ($36/200).
    Shit? Absolutely.
     
  8. Ken

    Ken Guest

    I can see 85Hz flicker.
     
  9. Adrian C

    Adrian C Guest

    How many LED's do I need to collect to be in possesion of a worrying
    amount of Arsenic?
     
  10. Usually, candles flicker because of turbulence. In most candle flames,
    the turbulence is a low order one and approximates a single frequency
    continuous oscillation, at maybe 6 Hz or so.

    I would think that putting random noise through a narrowband and
    highly resonant (which go together to some extent or another) 6 Hz
    bandpass filter, and have the output of that mixed with DC to power an LED
    of suitable color. (A candle flame has color and spectrum close enough to
    that of a 1900 K blackbody, maybe 1850 K for somewhat larger and more
    flickery flames.)

    - Don Klipstein ()
     
  11. I often like the bluish white light, though I expect to get tired of
    it if too many lights end up having that color. I hate it when too
    many holiday lights are of one particular color. And I have seen some
    nice ones at Target a year ago about the color of carbon arcs.

    As for the flicker - plenty lack fullwave rectification and so they have
    60 Hz flicker. I find that a little noticeable and a little irritating.

    I have seen some with better rectification - try to test them or see a
    sample plugged in at the store.

    - Don Klipstein ()
     
  12. krw

    krw Guest

    The fluorescent lighting in the store doesn't help. However,
    switching back to incandescents is guaranteed to eliminate the
    problem.
     
  13. Adrian C

    Adrian C Guest

    LED poisoning, ugh...

    </flump.....>
     
  14. Jasen Betts

    Jasen Betts Guest

    exposed lamp filament? (but it's PTC not NTC)
     
  15. Tim Williams

    Tim Williams Guest

    If they're not RoHS, it would be lead lead LED poisoning.

    Tim
     
  16. krw

    krw Guest

    Which brings up the obvious questions... Can one use LED indicators
    and be RoHS compliant? Is there a RoHS LED?

    Is there Arsenic in old LEDs? Are they RoHS compliant?
     
  17. That has flicker in USA having fundamental frequency 120 Hz.

    Those with vision sensing flicker at frequency that high on/near Earth's
    surface tend to be insects, aliens or other things than
    anywhere-near-typical human beings.
    I suspect very strongly that for close to 99% of humans, something more
    energy-efficient than that and economical is now available.
     
  18. Michael

    Michael Guest


    Many, many of the LEDs in DigiKey catalog are marked "RoHS Compliant"
     
  19. krw

    krw Guest

    Yes, and that flicker apparently masks the 60Hz flicker from the
    bulbs.
    I can easily see fluorescent flicker if it's close.
    No thanks. Burned once. $150 down a rat hole is several years
    worth of electricity for the incandescent replacements.
    Incandescents are an order of magnitude cheaper than new LEDs, so no
    savings to be had there either.
     
  20. MooseFET

    MooseFET Guest

    The frequency response of my fovea is not as fast as the rest of my
    eye. I don't see the flicker when I look directly at the tube. With
    just one tube, I can see it in the lighting of the room. Most two
    tube ballasts do a good job of putting about a 90 degree phase shift
    on the current to the two tubes so I only notice the flicker when one
    tube is out.

    The new "high efficiency" lights, that use the thin tubes don't make
    as much flicker. They just fail and burn out their tubes, flicker and
    flash in their own funny rhythm and draw a lot more current than the
    old ballasts did.
     
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