1. New to Christmas lighting? Get started with the AusChristmasLighting 101 Manual:
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  1. OP
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    BradsXmasLights

    BradsXmasLights WiFi Interactive

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    Not sure about that data sheet - either way it's WS2811 compatible which is 5V based signaling.

    I'll have to try a ESPixelStick with it and see if the GS8208 will take 3.3V signaling too. :)
     
  2. David_AVD

    David_AVD Bite my shiny metal ass! Community Project Designer Generous Elf

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    Those figures are the maximum working range (without damage) figures. Page 4 has the VIL and VIH figures although they seem to be somewhat screwed up. I think they mean VIL (logic 0) is 1V max and VIH (logic 1) is 4V min ? Maybe there's a more complete data sheet out there.
     
  3. Steve Hobley

    Steve Hobley New Elf

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    Hey thanks, I went with a 74HCT08 AND gate as a logic level shifter, and it seems to work OK. Nice clean 5v output.

    When I hooked up the board to the lights however, I get no LED output. When the power turns on, all the LEDs shine white for a fraction of a second, so I think they are good strips.

    When I measured the output from the ESPixelStick driver (NodeMCU from Banggood) I noticed that the edge to edge speed was 746KHz - is this too much drift from the spec 800kHz ?

    That's the only reason I can think of why the lights would not be working.
     
  4. Jorden Nash

    Jorden Nash New Elf

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    I'm having trouble getting my GS2808 pixels to work. I've tried them on a Falcon, Alphapix, and Joshua with no luck. 2811 pixels work fine on all of these, but not 8208. What is the string type and Kbps setting you use on a ECG-P12R?
     
  5. darylc

    darylc 404 darylc not found Global Moderator Generous Elf

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    Hmm they worked first time for me on Falcon - just wired in the power, ground and 1 data line.. sorry I can't be more specific I am traveling away from my pixels at the moment.
     
  6. zeph

    zeph New Elf

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    So this puts 3 single-color LEDs in series, and uses constant current drivers, thus allowing single pixels at 12v. That's a very interesting option and a new design.

    Think of it this way. Peak instantaneous current is pretty much the same regardless of color (thanks to the constant current driver).
    PWM modulation changes the average current tho. This would be the peak current times MAX(R,G,B) / 255, or perhaps / 256. All colors with the same maximum value would have about the same current.

    Suppose RGB = 120, 80, 30. Assume 2, 3, 3 volts Vfwd
    30 PWM steps = R+G+B driven in series at peak current (8v across RGB, 4v dissipated in transistors)
    50 PWM steps = B shorted, R+G driven at peak current (5v across RG, 7v dissipated in transistors)
    40 PWM steps = G+B shorted, R driven at peak current (2v across R, 10v dissipated in transistors)
    135 or 136 PWM steps = all off

    Increasing Blue to value 100 (or any value <= 120) would not change the avg current (significantly), because it's still turning on for 120 steps.
    But increasing Red to value 150 would increase the average current, regardless of the other colors (so long as they are less than Red)

    Thus (peak) current is flowing 120/255 of the time (or 120/256 depending on circuit), with different portions used by each colored LED and wasted by the Constant Current transistors.

    This makes it less efficient than 5V pixels, but more efficient than 12v BULLET pixels (which wasted 9 to 10 volts of 12). It could wind up being slightly more efficient than 5V pixels when full on.

    So it might take more POWER on average. But being 12v, one has a 2.4:1 advantage in current vs 5v so that reduces needed wire sizes or increases allowed length.

    So the typical GS8208 current is spec'd at 15mA per chip; at 30 pixels/m that's 450mA/meter @ 12v = 5.4 Watts
    Versus 30 WS2812b pixels per meter at 48mA (R+G+B) per chip = 1.44 A @ 5v = 7.2 Watts

    However, full blue would be the same as full white for the GS8208 but just 1/3 as much power as white for the WS2811.

    Note that wire gauge to handle max current is smaller, since the max current is about 1/3 as much; but the power supply would need to be capable of more total power.

    This could be worthwhile, because it allows smaller gauge supply / power injection wires, and can accept more voltage drop.

    Where it would really shine powerwise would be individual 12v pixels like bullets. Some people use 12v ws2811-based bullets now for the lower current + greater tolerance (albeit with greater total power). A GS8208 (or GS8206) based bullet would consume less maximum current by comparison. That is, you can run up to 3 colored diodes iin series from the same 15 mA, rather than needing to draw 15 ma/color for parallel. Think 100 RGB bullets drawing 1.5A, rather than 4.5A. (But you wouldn't be able to drop the 12v as low as with WS2811 bullet pixels, since you need to cover up to 3 Vfwd drops rather than just one).
     

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