circuit problems

Discussion in 'General Electronics Chat' started by spondootre, Sep 22, 2006.

  1. spondootre

    Thread Starter New Member

    Sep 21, 2006
    I've copied this circuit and I thought it was supposed to latch on with one press of the switch and off with another. However what I get running it at 12 volts is an output of 12v, then when the sw. is released it instantly drops to 0, if the switch is held on it drops to 0 after a few seconds indicating that the timer part is working fine. Any ideas?? Or is it supposed to do this?!

  2. hgmjr


    Jan 28, 2005
    Greetings spondootre,

    This circuit appears to be set up to respond to a pressing of the switch by generating a positive output pulse whose pulse width is set by the RC circuit.

    When you press the switch the output goes high immediately. You can then release the switch but the output pulse will stay high until the capacitor charges to the value needed to set the output pulse back to the low state.

    It is not set up to alternately toggle high and then toggle low with each depression of the switch.

  3. Gadget

    Distinguished Member

    Jan 10, 2006
    Remove the cap, resistor, and diode on the output of the second stage, and tie pin 10 to earth.
    You dont even really need the first stage... you could remove it and hook the switch (and it's de-bounce components) directly to the clock input of the second stage.