Need Suggestion For Lock !

Discussion in 'The Projects Forum' started by hzk17, May 3, 2013.

  1. hzk17

    Thread Starter Member

    Mar 20, 2013
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    I have asked for help in the forum regarding my circuit "One Transistor Based Lock" the feedback is really great, I have made this circuit about 3 times, now I have asked my teacher, he has allowed me to change the circuit, but it should be a lock. Now I should use Transistor, also now i am allowed to use a IC, but it shouldnt be a PIC. I am using a DPDT Relay 5V, when an incorrect combination is entered the buzzer will sound, and when the correct combination is entered a dc toy motor will be driven.

    So please direct me towards a circuit which will fulfill my need
    The Attached image of the circuit is the one which is worthless, the good people on this forum have pointed out the problems in the circuit diagram.
     
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Creating a new thread will not engender additional help. You already were asked to supply additonal info, but you did not:

    I will humor you though (and I hope a moderator will connect the threads).

    Your circuit should work. Can you tell us *how* it is not working?

    Here are some tips:

    1. Confirm your power supply is, in fact, outputting the correct voltage.

    2. Check continuity on your switch banks. The top set should be continuous when all switches are on, the bottom bank should be discontinuous when all switches are off.

    3. Measure Vb (the transistor base voltage with respect to ground). It should be 0 volts when the incorrect code is entered, and about .6 or .7 volts when the correct code is entered.

    4. Measure Vc (the transistor collector voltage with respect to ground. It should be equal to the power supply when the incorrect code is entered (assuming the relay is connected!), and about 0.1V when the correct code is entered.

    5. Measure the voltage across the relay coil terminals. It should be equal to the power supply (less about 0.1V) when the correct code is entered, and about 0V when the incorrect code is entered.
     
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  3. hzk17

    Thread Starter Member

    Mar 20, 2013
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    @joeyd999 Sgt.Rookie, he said in the earlier post as the diode cathode is on the +ve rail so if the supply is given inversely the diode would be Forward Biased, and therefore it would fry the transistor.
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Do you mean that if you reverse the supply polarity the transistor will fry? Yes that could happen, so that is why you don´t want to put reverse voltage into anything that isn´t specifically made to cope with it.
     
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  5. hzk17

    Thread Starter Member

    Mar 20, 2013
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    you are right
     
  6. joeyd999

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    Jun 6, 2011
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    Thanks. I missed that post (and, apparently so did OP).
     
  7. hzk17

    Thread Starter Member

    Mar 20, 2013
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    @joeyd999, my friend has made the circuit about which i am talking now we want to add a magnet, a miniature door would be added when the correct sequnece will be entered we want to demagnetize the holder or stopper of the door so that it could be opened. Can you tell me what is device called or do we have to magnetize some piece of steel or something.
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    If I understand you correctly, you want an electromagnet attached to the door frame that holds a metal piece attached to the door until you enter the correct code, right?
     
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  9. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    I know what you are talking about, but not what it's called. Sorry. But, essentially it is an electromagnet installed in the door jam, along with an iron plate attached to the door. Activating the magnet "locks" the door shut. Deactivating it allows the door to be opened. They are neat because there is no sound or click when the magnet is released, and there are no visible door latches.
     
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  10. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    As I remember these magnets from an RFID card operated door lock, they make a huge clang when the magnet is already activated and the door closes, so it may not be as neat in certain arrangements. And with the lock hzk17 has this will happen as it has no delay.
     
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  11. hzk17

    Thread Starter Member

    Mar 20, 2013
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    right @kubeek
     
  12. hzk17

    Thread Starter Member

    Mar 20, 2013
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    guys if you have any idea what would be this device called, please tell me ASAP
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Oh, the irony! ;) :D
     
  14. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    The ones I've seen (on professional office buildings) were able to sense when the door closed, and would then activate the magnet silently.
     
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