Problem with blinking LED

Discussion in 'General Electronics Chat' started by Gorvunkar, Jul 9, 2014.

  1. Gorvunkar

    Thread Starter New Member

    Jul 9, 2014
    4
    0
    Hello, I'm a newbie,
    I've done some simple projects. But there is one that I can't get to work.
    I want it to be solved before I can go on with my hobby.

    It's this one : http://www.instructables.com/id/Flashing-LED-using-555-Timer/?ALLSTEPS

    I built it exactly like that, but the LED isn't blinking, no , it gives off light continuously.

    The power supply is a lego train adapter.

    I've used the search function, this guy had the same problem : http://forum.allaboutcircuits.com/showthread.php?t=46620
    But my power supply is ok. Now, I read the sticky about decoupling caps.
    But it should work as described on that instructables site, right ?

    I used an NE555P and jumper wires (longer than on that site), all ordered from ebay.
    I tested the capacitor on the voltage. It simply reads a continous value : 1.4 V.

    What could possibly be wrong ? Are my IC's ok ? (Because I couldn't get a 4011 IC to work either, which I used in a project with multiple NAND-gates)
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    No offense, but a simple mistake is the most likely explanation. It's so easy to make a mistake and everyone here is nodding as they read this.

    Post a good clear picture of your build and maybe another set of eyes will see your problem. Decoupling caps would be a very good idea and should be easy to add. I also wonder what gauge wire you are using in your breadboard - does it fit snugly? If it's too thin, you can get poor connections. Try a 9V battery and see what happens.
     
  3. Gorvunkar

    Thread Starter New Member

    Jul 9, 2014
    4
    0
    aaah, it works with a 9 V battery.
    Thanks wayneh.
    Any idea why my lego train power supply behaves differently than the battery ?
    In other projects it creates normal results.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    It's making pulsing DC, with a high "ripple". You can use it if you filter that out. For instance, put a diode in series and then an electrolytic capacitor across the poles to store what passes thru the diode. (This arrangement is also used as a peak detector.) The capacitor will then look a lot more like the battery to your circuit.

    Lots of things like lights and motors don't care about the ripple, but something like a 555 that triggers based on sensing voltage, is going to lose its mind.
     
  5. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    Put at least 1000uF across the train PSU output and measure the smoothed DC to see how much higher on light load it is than the label says - then check the voltage rating of your capacitor to make sure it can take it!

    Raw (unsmoothed) DC won't help your circuit, and the smoothing capacitor will act as a peak detector giving rail voltage equal to the peak value of the AC - its probably marked in RMS, which is only 0.707 as much - add to that the regulation won't be anything special, so lightly loaded it might rise to more than the 555 max Vcc rating.

    The circuit will probably work just as well on 12V, so a 7812 regulator might help - or you can get 7808 types if you don't want to risk 12V.
     
  6. Gorvunkar

    Thread Starter New Member

    Jul 9, 2014
    4
    0
    Can you guys give a link with a scheme of how to do this exactly ?
    For now I use a rechargeable 9V battery.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    You really do need to learn how to use google.

    First hit:

    http://en.wikipedia.org/wiki/Diode_bridge
     
  8. adamclark

    Member

    Oct 4, 2013
    472
    6
    The very first project I built was a psu,, I chose a suitable transformer and went from there,, now it variable, high current and has the amps and voltage read our from lseg displays I used ic;s for,, and now a new addition,,,, an oscilloscope... the point is I started with a transformer and askedquestions until ive built what I have today,,,which is the basis for everything im doing now.... and the search button has become invaluable to me,,lol
     
  9. Gorvunkar

    Thread Starter New Member

    Jul 9, 2014
    4
    0
    Thanks, but you know what ?
    I did use google. It's all easy if you know the exact term to search for.
    You should take in account that
    - I'm a newbie
    - English is not my mother tongue.

    Those are also the reasons why I don't understand how I should decouple caps. And yes, I read the sticky, and I searched on google. But no, I don't get it. Can someone explain in a very simple way how to add them on this project ?
    [​IMG]
    I've built it, and only the LEDs that are placed directly on the ground rail of my breadboard (with one foot) blink, and the others which are connected with a short jumper wire don't.
     
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