triggering a 555 using 10 trigger inputs

Discussion in 'The Projects Forum' started by wtpovey1941, Jan 5, 2012.

  1. wtpovey1941

    Thread Starter New Member

    Jan 5, 2012
    Hi, I want to trigger a 555 monostable from multiple inputs which are derived from the outputs from the LM3914 set in dot mode Instead of using the led on each output I have 13k resistors. I have connected these outputs from each pin of the LM 3914 via an inverting buffer to their respective capacitors to the trigger input of the 555. So the trigger pulse is normally from high to low. The circuit only works when one or two are connected to 555. when 10 are connected the 555 is not triggered. What am I doing wrong. Please help, thanks.
  2. wayneh


    Sep 9, 2010
    I know you've described your circuit but please post a schematic. It will save a lot of words and get you to a solution much faster.
    wtpovey1941 likes this.
  3. Wendy


    Mar 24, 2008
    10 Inputs, 1 Output, what is the duration?
  4. w2aew

    Active Member

    Jan 3, 2012
    Bill - it sounds like the the load of the 10 buffer outputs is too low to be driven by any single output, so it's reducing the amplitude of your trigger pulse. Try using series diodes in each path to Wire-OR them together. I'm making the assumption that you've got 10 buffer outputs that you intend to drive into a single trigger input on the 555...
    Last edited: Jan 5, 2012
  5. wtpovey1941

    Thread Starter New Member

    Jan 5, 2012
    Hi Bill, The 555 monostable duration once triggered is 45 seconds Thanks Bill