RGB LED chaser - need theory help

Discussion in 'General Electronics Chat' started by yehezkel2, Oct 4, 2009.

  1. yehezkel2

    Thread Starter Member

    Oct 2, 2009
    well, my idea is creating a 10 RGB led chaser that has the following pattern

    first led fades to next color (red), second led fades to the same next color (red), 3rd, etc....
    after the last led has faded to the next color (red), the 1st led will fade to the later color (pink for example) and will be followed by the other 9 leds....

    i will control a single RGB led using a 4029 according to the following schem.
    just without the 555 part, leaving the CLK leg aside for the moment.
    (assuming that this is an rgb led moule, which will fade to the next color at every pulse on the CLK leg.
    from rainbow led

    now having 10 such modules,
    i will use a 4017 counter, common used in led chasers, to drive all the CLK legs of the 4029's.

    the 4017 will have a 555 timer that will set its CLK. every 4017's CLK will mean that the subsequent 4029 will change it's rgb led to the next color

    what do you say on the theory side ?
    will it work ?

    how should i connect the 4017's outputs to the 4029's CLK leg ? directly ? with a resistor ?

    i'm OK with the complexity and the cost due to the need of a 4029 circuit for every rgb led.

    i explain the pattern:

  2. Wendy


    Mar 24, 2008
    The 4017 and 4029 are both CMOS chips, which is to say they are compatible. The output of one will drive the input of another.

    I can't validate the circuitry without a lot more study, but your basic theory is sound. The LEDs in this case will turn on slowly and turn off slowly, It is possible to have them turn on fast and turn off slowly with the addition of a diode and some minor rearrangement around the transistor drivers.
  3. yehezkel2

    Thread Starter Member

    Oct 2, 2009
    ok, thanks.
    i like them fading in and fading out colors.

    my only concern is:
    let's say the 555 clock is 1 second between puleses,
    that means every 1 second the 4017 will jump to the next leg
    that means that each leg of the 4017 will be HIGH during 1 second,
    which mean that a 4029 will get its CLK by a 1-second long HIGH pulse.

    does it matter ? does it need a shorter pule to work ?
    i've read that the 4029 reacts on the RAISE of CLK, so the reaction is immediate to the clock, but i'm afraid that the 1-second long pulse will not be ok for it...

    any clue ?
  4. Wendy


    Mar 24, 2008
    The only thing that matters to the flip flop is the edge. Off the top of my head I don't remember which edge it triggers from, but it will be in the spec sheet.
  5. Audioguru


    Dec 20, 2007
    The CD4029 is clocked when its CLK pin goes high. The max duration of a clock pulse does not matter but its rise-time should be no longer than 5us to 15us. The output rise time of a 555 or a CD4017 is much faster so will be fine.