555 fault

Discussion in 'The Projects Forum' started by gjs, Oct 30, 2013.

  1. gjs

    Thread Starter New Member

    Oct 30, 2013
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    0
    I have built a basic circuit with a 555 timer to flash an LED on and off. The LED just stays lit. It does not flash on and off. Are there any tests for me to do ?
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    1,393
    The circuit is a standard 555 astable multivibrator, and will work if:

    R1, R2, and C1 are appropriate values,
    circuit is wired properly,
    and the 555 is not damaged.

    Most likely is a wiring error.

    What are the values you used for R1, R2, and C1? (If C1 is too small, the LED will flash so fast that it will appear to be on all the time.)
    Are you sure the LED is correctly installed with the anode toward pin 3 and the cathode through a current limiting resistor to ground?
    What is your power source and can you measure its voltage on pins 1 and 8?
     
  3. gjs

    Thread Starter New Member

    Oct 30, 2013
    2
    0
    I have worked out what was wrong. The time high was 60 seconds. I just wasn't being patient enough ! I have found a smaller capacitor so time high is now 8 seconds.

    thanks for your reply
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    That happens to me very often. :)
     
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