Multisim circuit breaks when a 555 square generator is just present in the circuit

Discussion in 'Homework Help' started by Abdi Rahman, Apr 30, 2018.

  1. Abdi Rahman

    Thread Starter New Member

    Apr 23, 2018
    Hi, I have a pretty bizarre problem with Multisim. I have a larger circuit which works perfectly when the inbuilt square wave generator for Multsim is used. I wish to replace the square wave generator with my own.

    I have a 555 square generator circuit which works perfectly when I test it by itself, the moment I recreate that circuit in the main circuit and connect it to a 5V source the output of the main circuit just stops after a few milliseconds. This only occurs when the square wave generator is connected to a source without even connecting it to the rest of the circuit, when I remove the 5V source the circuit simulates for a few seconds and then just stops the only way to get the correct waveform is to completely remove the 555 square wave circuit.

    The circuit is supposed to count up until the green wave form reaches the red and then it resets and starts again.
    Circuit with the square wave generator in the bottom left hand corner
    [​IMG] output when the 555 timer is disconnected from the circuit but the 5V source is connected
    output when the 555 timer is connected
    The correct waveform and what I am trying to achieve. My multsim file is here
  2. crutschow


    Mar 14, 2008
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Where is the Vcc source for the 555?
  4. Abdi Rahman

    Thread Starter New Member

    Apr 23, 2018
    @crutschow My apologies I thought I had posted it, I have narrowed the problem down to the 555 timer refusing to work with the staircase circuit so the file I am posting now contains only those two, if you connect a pulse generator circuit to the staircase circuit and disconnect VCC you should see the staircase circuit works as intended. @Alec_t I thought VCC was a source? The square wave circuit works when it is on a page of its own.

    Edit: Link