digital lock

Discussion in 'Homework Help' started by Gizew, May 22, 2008.

  1. Gizew

    Thread Starter Member

    Nov 29, 2007
    17
    0
    hi my friends, can u give me some additional information?
    i want to do aproject on digital lock. it operates when the user gives the passward. if the passward is wrong it will give sound using a bell.
    here is what i propose to do. i will use two comparator circuits(using only logic gates) and if the two inputs (0's and 1's )are the same the comparator output will be one and forces the lock to be opened. but if the passward is wrong the bell will ring. what i want additionally is to transmit messages or to call to the police station when the wrong passward is given. at this point i have faced a problem how to convert the word message to the 1's and 0's that the computer will understand. there are ASCCI codes to change but there must be a connection b/n the wrong output and the message.
    can you give me some ideas or other modifications. note that i will do my project using only logic gates and some ics that are constracted from them.
    thankyou.
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Dealing with your lock first: Your proposal, although vague, is the right approach. You could use XOR-gates (as many as numbers in your key-code) as comparators and then use NOR gates as control inverters connected to your bell.

    Dave
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Since humans often make mistakes, you might consider waiting until the third wrong password in a given amount of time before actually triggering the dialer. I don't know how things work in your nation, but here in mine the police do not respond to automated dialers - a third party monitors several dialer accounts and a human must talk to the police.
     
  4. Gizew

    Thread Starter Member

    Nov 29, 2007
    17
    0
    thanks for the first suggestion. i put it in my mind.

    but about the police station , i am not doing it practically. i am desgning the circuit. and i told u that by assuming.
     
  5. Gizew

    Thread Starter Member

    Nov 29, 2007
    17
    0
    thanks,
    but wuold u try the circuit?

    i planned to use a four bit number as a passward(0's and 1's)
    thanks Dave
     
  6. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Yes, so that is one XOR (as a comparator) per bit. The e-book covers this design: http://sub.allaboutcircuits.com/images/05314.png

    Obviously you are driving a bell and not a LED; furthermore you will need to move on to the transmission of messages - are you considering a microcontroller or something similar?

    Dave
     
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