555 w/ 4017 IC Troubleshooting Help

Discussion in 'The Projects Forum' started by Alb3rtV3, Oct 11, 2016.

  1. Alb3rtV3

    Thread Starter New Member

    Oct 11, 2016
    2
    0
    Hey Everyone,

    I am a new member here but I am no stranger to forums. So, my issue and I cannot figure this out. I used a circuit I got online to create an LED Chaser circuit. Everything seemed fine until I fire up the circuit. The LEDs chase...but they skip one over. I have attached a video as well as the schematic I used. Please let me know what you all think, I cannot for the life of me figure this out.

    [​IMG]

    [​IMG]
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Which one skips? The video does not show it.

    And BTW, you only need one resistor since only one LED is on at any time. Actually you don't even need that one, since the 4017 cannot source enough current to damage your LED.
     
    Last edited: Oct 11, 2016
  3. Alb3rtV3

    Thread Starter New Member

    Oct 11, 2016
    2
    0
    If you look closely, Output 1 and Output 3 seem to be skipped. Output 0 and 2 do engage. Its perplexing to say the least. But why only 1 resistor? Should each LED have one resistor per...
     
  4. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,801
    831
    Obviously the schematic and the breadboarded circuit are not the same. So it's impossible to comment without an accurate schematic.

    @wayneh explained why you need only one resistor. The circuit you show will only have one LED on at any given point in time. So you only need one resistor... One LED; one resistor!
     
  5. eetech00

    Active Member

    Jun 8, 2013
    648
    110
    Hi

    1. The 4017 can only output 6ma max per output. Try changing the resistors to 1k ea.
    2. I would recommend using 1 resistor per LED as you've done or use a resistor pack.
    3. Connect a resistor and cap in series (10k resistor to gnd, 0.1u cap to +v) . Connect the junction to the reset pin of 4017
    to ensure the count always starts with 0.
    4. If you need more output current, you can use two ULN2004's connected to the outputs of the 4017.
     
    Last edited: Oct 11, 2016
  6. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    In simple terms you connect all the LED cathode's together and put resistor between that connection and ground. I would add a 10uF capacitor between Vcc and ground near the 555 also.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Guys, he has a skipping problem not a resistor problem. Don't make me regret mentioning the redundant resistors.

    Oops, never mind. I see you both addressed the need for decoupling capacitors.
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,972
    744
    I only see 4 Red wire outputs, clearly your built circuit is not the same as the diagram.

    You could have put the leds in reverse by mistake.
     
  9. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,501
    380
    hi
    I agree with Dodgy, only 4 Red wire drivers.???
    E
     
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  10. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
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    The protoboard circuit is very different from the post #1 schematic. Looks like 4 banks of 3 LEDs in series.

    ak
     
  11. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Could easily be a pinout problem. We need better photos.
     
  12. Colin55

    Member

    Aug 27, 2015
    191
    19
    Put 100n on pin 5
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
    1,247
    If you mean placing a 100 nF capacitor from the 555 pin 5 to ground, that will have no effect on either the circuit in the schematic or the circuit in the video in post #1, and is not related to the problem being described..

    ak
     
  14. hp1729

    Well-Known Member

    Nov 23, 2015
    1,944
    219
    The output of the 555 is going to be a really short low pulse. I suggest a resistor between the Discharge and Threshold/trigger inputs.
     
  15. eetech00

    Active Member

    Jun 8, 2013
    648
    110
    I agree. If just one LED in a series string is reversed, the whole string won't light.
     
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