The 555 Riddle: My 555 wont work, I've tried everything!

Discussion in 'Digital Circuit Design' started by Barrythecableguy, Jun 23, 2016.

  1. Barrythecableguy

    Thread Starter Member

    Jun 14, 2016
    31
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    Thank You all for your kind help in resolving my previous capacitor issues, I now have a new challenge and I am completely stumped. This time it concerns the “555 IC” This thing is driving me mad, I’m trying to get it to run in “astable mode” in order to make an LED blink on and off, its mission impossible! I have viewed at least half a dozen circuits and built them exactly as instructed and the light will not blink on and off, it just comes on and then stays on! I have used the same value resistors, the same value capacitors, the same wires and the same power source as instructed. At first I thought it might have been the timer itself and so I used ten separate 555’s and the result was the same with every one of them, I’ve used different breadboards, I’ve used polarized wires and non polarized wires, I’ve tried different power sources, I even tried using a closing switch and even an LDR, nothing absolutely nothing will make my little LED blink on and off, everyone else’s blinks why won’t mine ? I am so desperate to fix this that as god is my witness I will give $10 to whoever helps me solve this! How can something so simple be so difficult, there must be someone out there who can get to the bottom of this apparent curse, someone step foreword!

    The pictures are of my own attempts to build the circuit.

    [​IMG]
     
  2. Marley

    Member

    Apr 4, 2016
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    Are you sure that it's not flashing too fast to see?
    Post your circuit diagram and component values.
     
  3. Barrythecableguy

    Thread Starter Member

    Jun 14, 2016
    31
    1
    Here it is, i'm not great at reading circuit schematics but I went from what I saw

    Barry



    R1: 4.7K Ohm resistor

    R2: 4.7K Ohm resistor

    R3: 1K Ohm resistor

    C1: 100 μF capacitor

    upload_2016-6-23_16-12-58.png upload_2016-6-23_16-13-28.png
     
  4. OBW0549

    Well-Known Member

    Mar 2, 2015
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    (Referring to your original post) Try changing the resistor between pins 2 and 7 to 100 kΩ and see what happens. As it is, right now you appear to have a 2.2 kΩ resistor in there, meaning that no matter what the oscillation frequency is, the LED is going to be lit approximately 98% of the time.

    Also, what is the capacitance of that electrolytic at the bottom of the picture? If it's too small, the oscillation frequency may be so high that you can't see the LED blinking on and off. Given your 100 kΩ resistor between pin 7 and Vcc, I'd recommend 10 μF or more.
     
  5. Barrythecableguy

    Thread Starter Member

    Jun 14, 2016
    31
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    I've been using 470 μF and in one instance I even used a 1000 μF electrolytic, I tried a 10 μF electrolytic last night and it was the same result, no blinking.

    Barry
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Are you sure you have the LED the right way round (cathode to V-)?
     
  7. Barrythecableguy

    Thread Starter Member

    Jun 14, 2016
    31
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    Yes for sure its facing V- No doubt.
     
  8. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Build it like this and it will work.
    NE555 Simple Astable.JPG
     
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  9. Alen Glenie

    New Member

    Jun 22, 2016
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    I don't see a cap on pin 5 to ground. 10uf should be there? Perhaps its a bad board?
     
    Last edited by a moderator: Jun 23, 2016
  10. WBahn

    Moderator

    Mar 31, 2012
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    While bypassing pin 5 is a very good idea, it shouldn't make much difference regarding whether the circuit will work, just how well behaved it is in terms of matching timing expectations.
     
  11. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Below is your "As Built" indicated in astable-1.jpg.

    Tracecom has provided you with a better circuit. You have not indicated the frequency or duty cycle in your design.
     
    Last edited: Jun 23, 2016
  12. Barrythecableguy

    Thread Starter Member

    Jun 14, 2016
    31
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    Thank You very much, ill look into this tonight

    Barry

    No, no luck, iv used a 100 kΩ resistor and a 10 micro F electrolytic and the result is the same.

    Any more suggestions ?

    Barry

    I am currently using "555P" rather than "555N" will this make a difference ?

    Barry
     
    Last edited by a moderator: Jun 25, 2016
  13. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Did you build the circuit as described by tracecom?

    Show us your breadboard.

    The 555 should not make a difference.

    What is the voltage on your 9 volt battery?
     
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Are you using a fresh battery?
     
  15. Barrythecableguy

    Thread Starter Member

    Jun 14, 2016
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    Yes the battery is fresh, c,mon guys there is still prize money to be won. and my light still will not blink, someone must have the answer!

    Barry
     
  16. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I can assure you that if you build the circuit in the schematic I posted, it will work unless:
    1. one or more of the components is damaged, or
    2. you made a wiring error, which is by far the most likely scenario.

    You continue to post that it won't work, but you don't answer the questions being asked.
    A. Did you build the circuit I posted?
    B. Did you substitute any components, and if so, which ones, and what values did you use?

    Finally, you don't post a photo of your breadboard.

    Like most of the other posters here, I don't have any interest in your prize money. I am just trying to help.
     
  17. JohnInTX

    Moderator

    Jun 26, 2012
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    Joe, you show R1 as 10K, in the picture it looks like 100K to me. That would make the ON time way longer if so.
    Also, in astable2.jpg, it looks like the timing cap is connected to pin 1, not pin 2 as it should be.
    But my eyes aren't as good as they used to be....
     
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  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Not all breadboards are configured the same. Have you checked that your + and - rails go the full length of the board and are not sub-divided?
    Breadboard contacts can go intermittent, especially if over-size wires have been forced into them. Try repositioning component legs and interconnecting wires.
     
    Alen Glenie likes this.
  19. Barrythecableguy

    Thread Starter Member

    Jun 14, 2016
    31
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    Ill work on it in more detail over the weekend and get back to you.

    Barry
     
  20. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I know that you said you are new. If you are really interested, you need to learn to read a schematic drawing. To that end, I have built the circuit on a solderless breadboard and posted a photo below. My suggestion would be to print out the schematic I previously posted and compare the schematic to the photo and to your own assembly. I find that when I build a breadboard, it helps to use a highlighter to mark each component and connection on the schematic as I add it to the breadboard; then, when all the components and connections are highlighted, my breadboard should be complete and correct. But we all make assembly errors from time to time.

    And my breadboard works perfectly as shown in the photo. The LED flashes continually at about 1 Hz.
    NE555 Simplified Astable Multivibrator.jpg
     
    Last edited: Jun 25, 2016
    Sinus23, GopherT, Bernard and 5 others like this.
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