555 timer problems

Discussion in 'The Projects Forum' started by popto, May 16, 2009.

  1. popto

    Thread Starter Active Member

    May 1, 2009
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    I have been trying to make a flashing led circuit using a 555 timer. I have not been having much luck. I set it up on my bread board as shown here. except that I am just running one led not two so I omit one of the leds and one of the resistors. the resistors that I did use were both 10k. I tried several different capacitors but none of them worked right. I tried electrolytic ones from 10μf to 100μf, using them the led stayed on. I tried some plastic film ones with the same results. some of the ceramic ones that I tried made the timer run one cycle but didn't repeat, so when I put power to the circuit the led stayed on for 10 seconds then turned off and stayed off.

    I have also tryed to set it up as shown on some videos on Youtube and had an equal amount of success.

    One really strange thing happened while I had it set up as I described first (not the one from youtube). Once I left the power on to the circuit while I changed capacitors and as I was putting the new capacitor in (before I had made contact and wasn't touching anything) the led came on!!! After some experimenting I figured out that if I left everything normal except for no capacitor and then moved my finger close to but not touching the insulated jumper wire between pin 6 and pin 2 the led would come on. I also discovered that it wouldn't work if my feet weren't touching the ground. This is very interesting but completely useless except for some kind of security device and it doesn't get me any closer to a flashing led.


    The only thing that I can think of that may have gone wrong is that all the capacitors that I have I desoldered off of old circuit boards. the 555 is new so should still be working. I am getting really frustrated at this circuit and have been tempted to throw the whole thing out of the window.:mad:

    if there are any questions about how I set something up please ask.

    please help:confused:
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Where did you place the two 10K resistors?

    Where is the LED connected?

    Are you sure you have the proper connections?
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    I've been continuing these AAC experiments. Check this out...

    The 555 Projects
     
  4. popto

    Thread Starter Active Member

    May 1, 2009
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    the 10k resistors are between positive side (12v) and pin 7, then between pin 7 and pin 6. the led is connected from pin 3 then to it's own 1k resistor then to the negative. All my connections should be fine because I am using a breadboard.
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    I think your connections are not fine because you are using a breadboard.:p

    Make sure you know how the holes on the breadboard are interconnected.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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  7. popto

    Thread Starter Active Member

    May 1, 2009
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    I just double checked my connections and they are fine. I know how my breadboard works.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Are you using a CMOS 555?
     
  9. heavyarms666

    Member

    May 16, 2009
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    hey.. i also have that problem before, some say we have a static charge in our hand, it can damage the ic(i thought)..
    make sure that there is real connection to the pin 2.. U may connect it directly at pin 6 or just put a 'pull up resistor and a switch to the ground' in that pin.. you can try also to put a 1k resistor between pin3 and led to stabilize the output..
    make sure that the capacitor is not busted, overheating it will result to a damage.. dont forget to check it first with a VOM.. and i before i forgot, put also a 1uF between pin5 and ground, it will help a lot
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    If you are using a CMOS 555, it sounds like that pin 2, 4, or 6, or some combination of them, is not properly connected as shown in the schematic. Floating CMOS pins are very sensitive to body capacitance, and can cause some really weird behavior.
     
  11. popto

    Thread Starter Active Member

    May 1, 2009
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    :)I got the timer working using another circuit design. Thank you all very much for your help. I'm not quite sure why this circuit works and the other one didn't. I will go back and compare them and see what is different and what is the same. Right now it works fine so do I still need to put a capacitor between ground and pin5? I learned that the 555 was supposedly sensitive to static after I held one in my hand and other stuff like that. I thought that I had ruined it (I also dropped that particular one on the ground) so I bought another one. Just a few moments ago I substituted the old one in the new (working) circuit and it worked too. So how careful do I really need to be with these 555s?

    Thanks again.:)
     
  12. mik3

    Senior Member

    Feb 4, 2008
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    You have to be careful with all CMOS technology ICs because they are sensitive to static electricity and spikes. A quite high voltage brakes the silicon dioxide down and the IC is gone.

    It would be good to touch a grounded metallic object before working with CMOS ICs.
     
  13. memyselfandi

    New Member

    May 22, 2009
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    Please excuse my interuption but I am a newbie to the 555 and I will say that I need some major help. I need to build an automatic playback circuit that plays every 10 minutes but I don't know where to start. I have seen this done but did not see it first hand, Please help me figure this out, I already have the recording module but I need to build the other half that triggers and auto resets every 10 minutes. Thank you in advance.

    JP
     
  14. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Welcome to the forum, JP.
    What you're doing is called Hijacking a thread. It is not polite to use someone else's post to post your own question. Please post your own New Topic.
     
  15. memyselfandi

    New Member

    May 22, 2009
    8
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    Please accept my appologies as I found this page with the search engine and registered and it brought me back here. Once again I do sincerely appologize.
     
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