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Help with LED strobe

Discussion in 'LEDs and Optoelectronics' started by peter.s, Dec 18, 2014.

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  1. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    That looks good. Don't forget to heat sink the FETs.
     
  2. peter.s

    peter.s

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    Dec 18, 2014
    I've just finished soldering this project together and although it looks a little like Frankenstein's monster - it works pretty well :)

    Except it flashes only twice per side - not three times as I expected. What could I have done wrong? I've checked my work but can't see anything obvious.

    Also - It is flashing too fast for what I want it for, do I need to increase or decrease the values of R1, R2 and C1?

    Cheers...
     
  3. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    I can't see anything wrong from here (too much dirt and rock in the way).
     
  4. peter.s

    peter.s

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    Dec 18, 2014
    Very funny... :)

    I've been reading about the 555 controller here (http://www.doctronics.co.uk/555.htm) and a sample diagram they provide is identical to the one I'm using, except they have pin 7 between R1 & R2. Where as I have pin 7 after R1 & R2 combined - does that make sense? Perhaps that would be my problem?
     
  5. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    Or it could be any of a variety of things. It's generally not useful to analyze a circuit for faults based on a verbal description provided by the same person who, presumably, built in the flaw(s). Since my previous humorous attempt to suggest it was lost on you, let me use the word "photograph".
     
  6. peter.s

    peter.s

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    Dec 18, 2014
    Your humour was not lost on me - I am just bashful about posting a picture of my little monster… and expectant that you may not be able to make head nor tail of the mess :). I have limited access to electronic equipment, so I had to make do with what I could get my hands on.

    For testing I have it connected to 5VDC, 1A. The little LEDs are only for testing, I don't yet have the LEDs I intend to be using. The ICs are not facing the same direction - I know this is bad form but… I'm a novice.

    I've looked at the logic diagrams of each component (555, 4017 & 4075) and totally follow the overall logic of this set up. My monster seems to be put together right, so the fact that it is flashing only twice per side has me stumped.

    Strobe-1.jpg Strobe-2.jpg
     
  7. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    That is difficult to make sense of. I'll bet I would find a ready market for breadboards in Prague. The best guess I can make is that there are some connections between the 4017 outputs and 4075 inputs that haven't been made.
     
  8. peter.s

    peter.s

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    Dec 18, 2014
    Strangely the word Breadboard is not in my Czech phrase book :)

    I tested all my connections and they were good. So I tried another combination - outlined by Kris in his diagram posted in the thread I referred to in my first post (https://www.electronicspoint.com/threads/12v-led-strobe-controller.254837/).

    I now have (from 4017) pins 2, 7, 1 going to (4075) pins 1, 2, 8 respectively. And (from 4017) pins 3, 5, 9 going to (4075) pins 3, 4, 5.

    I think it is now doing a triple flash - but it is so fast it is very difficult to tell.

    To slow this thing down I am planning on using R1=1kohm, R2=68kohm & C1=1uF... I'm trying to get it to flash at about 1 second per side, that is 1 second per triple flash.
     
  9. peter.s

    peter.s

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    3
    Dec 18, 2014
    I've slowed it down and it is definitely doing a triple flash - in fact it may have been flashing properly with the first pin combination, but it was flashing so fast it was impossible to tell.

    I've been reading up on the 555 timer and experimenting with the values of R1 & R2 to get different flash cycles, but I'm not sure I fully understand the relationship they have with C1. I've kept C1 as 2.2uF (as from original schematic) and vary R1 & R2 - is there any point in changing the value of C1 if changing R1 & R2 already changes the flash cycle?
    What would giving C1 a higher value do?
     
  10. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    A larger capacitor slows the timing.

    The capacitor is a tank of energy that's being filled or emptied. The rate of that process is controlled by the resistors.
     
  11. peter.s

    peter.s

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    Dec 18, 2014
    Thanks KJ6EAD, I thought as much.

    A quick question about the 4017. Is there a reason why the pin-outs from the 4017 are every second pin in the firing order? To be more clear - the firing order of 4017 is pins 3, 2, 4, 7, 10, 1, etc. and the strobe set up uses pins 3, 4, 10 for one side of LEDs - skipping pins 2 & 7. Why not use pins 3, 2, 4 - as they are directly consecutive in the firing order?
     
  12. KJ6EAD

    KJ6EAD

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    159
    Aug 13, 2011
    The unused pins make the off times in the sequence. Try connecting an LED and appropriate limiting resistor to one of the unused pins (other end to ground) and see for yourself.
     
  13. peter.s

    peter.s

    37
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    Dec 18, 2014
    I think I've just discovered the importance of having a breadboard :)

    Playing around with this has led me to try and change the flash pattern slightly - I'll see how I go and perhaps start a new thread if I get into trouble.

    Thanks so much for your help KJ6EAD - I've learned a LOT!! :)
     
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