combination lock

Discussion in 'The Projects Forum' started by onebird, Apr 7, 2010.

  1. onebird

    Thread Starter New Member

    Mar 27, 2010
    I am currently working on an electronic combination lock circuit that operates as follows:
    A user enters a four digit code that goes through a decimal-to-binary encoder. Because there are four input digits, it means that there are four identical comp[arator circuits. whenever an input is applied a pulse is sent to a counter circuit that switches the input from one comparator circuit to the next. This should be clear from the attached circuit. the problem is just that when the input of the fourth digit is applied to the fourth comparator - the counter returns to the first comparator and so implying that the fourth number is placed at the first input. The idea is to have a circuit that is always ready to accept the input from the user at any time, so I am having trouble trying to stop the fourth input from interfering with the first input. Can anyone help me on this one?
    NB: The circuit has a facility for changing the preset code, using the SR flipflop near the bottom, which is working perfectly-it turns off soon after the fourth number is stored.