Questions about SgtWookie's 555 schematic

Discussion in 'General Electronics Chat' started by RiG615, Dec 1, 2008.

  1. RiG615

    Thread Starter Active Member

    Nov 13, 2008
    I got a few questions about this schematic

    so R1 and C1 adjust how long the initial on delay is and R2 and C2 adjust how long the pulse is?
    and then is it all over, or does it repeat? i cant really tell which mode each of these are in, monostable or astable? confused about R3

    One more thing - in IC1 the trigger connected to pin2, is it a momentary switch? and is it connected to ground or Vcc?

    Thanks a bunch, ive been doing a lot of reading to try and understand these 555 chips
    -Beenthere -ill save you the trouble this time (by making a new thread)
  2. Wendy


    Mar 24, 2008
  3. RiG615

    Thread Starter Active Member

    Nov 13, 2008
    How does this schematic operate
    is it- once triggered there is a delay and then a pulse and then it ends and does not repeat
    correct or no?
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    To determine if 555 ckt. is one-shot or free-running ,check source of pin 2's input, if it's external to the ckt. then probably one-shot, if it is connected to timing cap. it's feee-running. R3 is part of a differentiator to produce a negative pulse on the trailing edge of IC 1 pin3 output pulse. The trigger ,2, is a level input so that it can follow the rising v. on charging cap., or can pe triggered by a - pulse.
  5. SgtWookie


    Jul 17, 2007
    I somehow missed this thread. Easy to do, since I'm not on here all the time.

    That circuit was created using Schematica's 555 Timer Pro in the "Lite" mode (freeware)
    You can download it here:
    A number of options aren't available in the "Lite" mode, but you can use it indefinitely as freeware.


    It's actually monostable.

    It could be.
    If you wanted to use a pushbutton switch to control it, that would work. You could connect a 10k resistor across pin 2 and Vcc, and also connect a N.O. pushbutton between pin 2 and ground. The 10k resistor would keep Vcc on pin 2 until the button was pressed. Pressing the button would ground pin 2, starting the timer.