I need help to figure out this schematic

Discussion in 'The Projects Forum' started by Mussawar, Apr 11, 2013.

  1. Mussawar

    Thread Starter Member

    Oct 17, 2011
    68
    3
    Hi, following is a part of schematic (please see attachment). 555 is a delay off timer. When power is supplied to timer it energizes the Relay for 10 seconds. Timer itself and other parts are working fine. Yellow 9V supply line is always available to circuit. Red supply line is occasionally available. The goal was to “turn OFF the timer circuit when the RED supply is present and vice versa”. But here PNP transistor is not working properly. I thought it would cut off the timer’s power; when RED supply is present by turning its base high but it is not working as it was supposed to work. Probably I’ve selected the wrong values of biasing resisters. I’ve tried different values of base resisters. Sorry, I’m not expert of electronics and always need suggestions. Some body please trace out the fault. Where I am going wrong? Thanks and regards.
     
  2. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    Perhaps this?
     
  3. Mussawar

    Thread Starter Member

    Oct 17, 2011
    68
    3
    :) Hi, Thanks for suggestion. Grounding RESET pin is a good aproach but it'll not triger the timer every time when it is needed. regards
     
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