Disabling pushbutton

Discussion in 'The Projects Forum' started by nivekevin, Oct 8, 2010.

  1. nivekevin

    Thread Starter New Member

    Oct 5, 2010
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    Hello,

    Its pretaining to my project assignment....
    How do I disable a pushbutton temporary for 5 seconds? Meaning during these 5 second, pressing the pushbutton will have no effect on the whole circuit at all... then it is after 5 second have passed then the push button will be working again?

    Pls advise. I am really unsure of how to implement it... :confused:
     
  2. wayneh

    Expert

    Sep 9, 2010
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    That's called de-bouncing, and can be accomplished with a standard 555 circuit. (Just search for 555 debounce).

    [edit] I think the debounce is the same as holding the button down for that time. Is that OK?
     
  3. nivekevin

    Thread Starter New Member

    Oct 5, 2010
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    Hmmm... I'm still not sure on how to do it...

    Like me explain further... I have a circuit that check whether two passwords are the same. If they are the not the same, I would need to disable the circuit for 5 seconds...

    Meaning that if the pushbutton is disable... then the circuit cannot read in any password value anymore for the 5 secs... after the 5 sec, the passwords can be read once again...
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    What signal would start the 5-second timer?

    Ken
     
  5. mcgyvr

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    Oct 15, 2009
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    You have some sort of micro correct? If so this can all be accomplished on the software side.
     
  6. nivekevin

    Thread Starter New Member

    Oct 5, 2010
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    Sorry.. i dun know what does micro correct means.... T_T...
     
  7. retched

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    Dec 5, 2009
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    He meant:

    You are using a MicroController, correct? If so, you can write some code in software to disable the keypad input pins for 5 seconds after the last password is checked.

    ;)
     
  8. KMoffett

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    Dec 19, 2007
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    mcgyver was asking if your security/password circuit was being on a programmable micro-controller chip. Can you explain what the whole project, hardware and software, involves?

    Ken
     
  9. retched

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    Dec 5, 2009
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    If this is a quest into flip-flop and logic gates, the disable could be an interesting task. I agree with KMoffett, an explanation of the project will keep us from burning off too much oil running in circles.
     
  10. nivekevin

    Thread Starter New Member

    Oct 5, 2010
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    My project is about using flip-flops and logic gates to design a circuit... Micro-controller is not allowed at all in my task...

    Let me provide you with the question:

    After September 11 attacks, there is an increased demand for security systems to control access to the cockpit while the plane is in the air. Retina image analysis based biometric systems are becoming increasingly popular for security applications. In Digital Airlines, only designated cabin crew members can open the cockpit door by being subject to a retina scan followed by a PASSCODE entry. The image processing subsystem encodes the retina image as a 4 bit VALUE (given to the system using a 4-bit DIP switch, and read upon pressing an OPEN pushbutton). In the next clock cycle, the 4 bit PASSCODE from the user is read in (given using the same DIP switch). If the VALUE is greater than the PASSCODE by exactly 5, entry is granted (shown using a GRANTED LED); otherwise, the system is disabled (which can be optionally shown using an LED) for 5 clock cycles. A further failed attempt will LOCK (shown using a red LED) the system completely, and will not be active until the technicians perform a manual reset to the system after landing (to be simulated using a RESET push button).
    [Note: There is no need to account for overflow in arithmetic operations.]
    [Hint: you may have to use a clock slower than 1 Hz for giving input accurately]


    The red words is the issue that I have been concerned with regarding disabling the pushbutton.. which i think will be effective in disabling the system...

    Pls advise.

    Thank you!!! :)
     
  11. retched

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  12. nivekevin

    Thread Starter New Member

    Oct 5, 2010
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    Hmmm.. actually I have already implement the counting using a 74191 counter... I cannot use too much flip flops because I am limit to only using 12 MSI Chips in the whole design...

    Hmmm... let me attach the schematic that i have developed so far for the project that I am working on...
     
  13. KMoffett

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    Dec 19, 2007
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    I would say a simple 5-second monostable, or counter tied to your "system clock" (?), disabling a line to or from the keypad. But it gets a little tricky to design a circuit to attach to an unspecified, imaginary circuit.
    Can you post a schematic?

    Ken
     
  14. Wendy

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    Mar 24, 2008
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  15. nivekevin

    Thread Starter New Member

    Oct 5, 2010
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    I already attached my schematics in my previous post (in PDF version).
     
  16. nivekevin

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    Oct 5, 2010
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    Actually I have already implemented a 555 clock timer.... its jus that in my schematics... I used a pulser instead to model the behavior of a 555 timer.
     
  17. Wendy

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    Mar 24, 2008
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    I looked at the PDF, the schematic for the 555 is not in there. Since there are several schematics for 555 monostables I wouldn't assume.
     
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