Led sequencer problems

Discussion in 'The Projects Forum' started by popto, Jun 27, 2009.

  1. popto

    Thread Starter Active Member

    May 1, 2009
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    Hi,

    I built the 10 led sequencer described here in the first picture. I am pretty sure that I put it together correctly but there are some problems. First I think I should mention that I am using a home made power supply to power the circuit and that it is very close to the breadboard that I am working on.
    I have my power supply on 9v and the circuit seems to just run randomly. It will have one led on then all the leds will light a little bit then the first led will be back on, and that just keeps happening. I was getting very frustrated at it but I did discover that if I turned my power supply down to 6v the whole circuit would run fine.

    I just noticed that the voltage on this specific circuit is actually 6v. I feel incredibly stupid.:mad: I have see other similar circuits that had shown 9v for the power and hadn't noticed that this one was 6v. oops. I guess I just fixed most of my problem. oh well, I just wrote all of that so I may as well ask another question. I tried hooking this circuit up to a 9v battery and it worked. Why does it work on a battery when it wouldn't work on 9v from the power supply?

    thanks for any and all feedback,
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Can you post a schematic?
    Do you have decoupling capacitors at each chip?
    These should be 100 nF and be connected as close as possible to the ground and power points of the chips.

    Greetings,
    Bertus
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    The circuit is missing a bypass capacitor (decoupling capacitor) for the power supply voltage. Maybe the power supply that caused trouble has very poor filtering of its rectified AC.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What Audioguru said - or the wires from the power supply to the breadboard were more than a few inches long.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Yes, the 555 and the 4017 should not have problems with 9 volts - or even 12, for that matter.
     
  6. popto

    Thread Starter Active Member

    May 1, 2009
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    0
    I tried the simplest thing first which was shortening the wires. I bypassed the probes that come out of the power supply and just used alligator clips to connect the circuit and it worked fine on 9v but still wouldn't work on 12v. So I bypassed the alligator clips and just used short (3 inches) jumper wires and it worked at 12v volts as well.

    thank you all for the advice.

    I was just wondering, why do long wires mess up these two circuits? Is there a way that I could use long wires and have these circuits still work? one last question, why does the size of the capacitor on the 555 timer make a difference on how well the 4017 circuit works? when I put a slightly larger cap on the 555 the 4017 seems to just skip an led every now and then, but when I have a very small one on the timer the 4017 works fine.

    thanks everybody. I really appreciate your willingness to answer my dumb questions
     
  7. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    what size wire ?? sounds like the voltage control on your homemade ps is backwards....?
     
    Last edited: Jun 28, 2009
  8. popto

    Thread Starter Active Member

    May 1, 2009
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    0
    the wire that I used for the probes is salvaged out of an old 220 extension cord and are about two feet long. Would that effect anything? how can the voltage control be backwards? What would it effect? What is it for that matter?

    thanks
     
  9. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    wow, i guess that wire should handle that led current.

    i ask about the controls because it almost seem like when you crank it to "12" its being under voltage and not driving the IC's enough, etc.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    Helo Popto,
    Look at the datasheet for the LM555. It says it needs to have two supply bypass capacitors (to stop associated circuitry from messing up like your CD4017 did).
    One capacitor should be a 0.1uF ceramic disc for high frequencies and the other should be at least 1uF electrolytic. They should both be mounted very close to the 555 supply pins.

    The datasheet for the Cmos 555 the ICM7555 explains that the ordinary 555 creates a 400mA supply current spike when its output switches. The supply bypass capacitors hold up the voltage during the 400mA spikes. The inductance of a piece of connecting wire for the supply voltage would allow the voltage to drop at the IC if the bypass capacitors are not nearby.
     
  11. popto

    Thread Starter Active Member

    May 1, 2009
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    ok, thanks. how do you tell the value of the ceramic capacitors?
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    A ceramic capacitor marked "104" is 0.1uf. The letter J is 5%, K is 10% and M is 20% tolerance.

    102 is 0.01uF, 103 is 0.01uf and 105 is 1uf etc.
     
  13. bertus

    Administrator

    Apr 5, 2008
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  14. popto

    Thread Starter Active Member

    May 1, 2009
    44
    0
    I put the capacitors where they were supposed to be and it works fine all the way up to 12 volts now. thank you all for the advice and thanks for the links about capacitor coding.
     
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