555 Timer Output PIN 3 permanently high

Discussion in 'The Projects Forum' started by voldeparso, May 27, 2016.

  1. voldeparso

    Thread Starter New Member

    Apr 10, 2016
    6
    0
    Hello, I have a question, what are the reasons for permanently high output from a monostable configuration of 555 timer?
    upload_2016-5-27_23-18-4.png

    I have this circuit activated by a clap, and the 555 output goes high after one clap and never goes low after that. Can you help me?
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,516
    1,246
    To start with, there is no DC reference potential on the + input to the 741. Also, the 741 output cannot swing all the way down to its negative power rail on pin 4, so Q1 night not be turning off.

    ak
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,990
    3,226
    What's the voltage at the TR input (Pin 2) after the clap?
     
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