555 Timer Help

Discussion in 'General Electronics Chat' started by BlackCow, Jan 22, 2010.

  1. BlackCow

    Thread Starter Active Member

    May 11, 2009
    I'm trying to figure out a 555 circuit that, when the input goes low the output will not go high until lets say 30 seconds. The output then needs to stay high until the input goes high again. (fixed, sorry t_n_k)

    Is this all possible around one 555 timer? This seems like it should be simple but I'm having issues trying to figure it out :(
    Last edited: Jan 23, 2010
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    This doesn't make sense.
  3. iulian28ti


    Dec 4, 2009
    SO... (odd request man...)
    input to low -> 30sec delay -> output to high
    input to high -> output to low

    well, you don't need an actual 555
  4. BlackCow

    Thread Starter Active Member

    May 11, 2009
    Ahhh I guess I was going in the wrong direction with the 555 for a time delay circuit. I'm having a bit of trouble following your schematic but I guess you are using the OP amp to compare the charging voltage to the +5 volts to turn it on?

    I think I can figure things out from here, thanks man.
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    I think this does what you want:
  6. Wendy


    Mar 24, 2008
    Pretty close to what I was thinking except leave off C2, and possibly R4 if it is being feed from a digital output. A 555 will stay high (inverted from the OPs request) while the input stays low after the monostable has timed out, which is why signal conditioners are usually part of the input. The monostable triggers on the negitive edge.

    Bill's Index

    The 555 Projects

    555 Monostable
    Last edited: Jan 23, 2010
  7. BlackCow

    Thread Starter Active Member

    May 11, 2009
    Ah perfect! Thank you so much. :D

    I guess what I was trying to ask for specifically was a time delay circuit, sorry for the confusion. And thanks for posting some alternatives without a 555 :)