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    This simple code lock circuit described here is of an electronic combination lock for daily use. It responds only to the roght sequence of four digits that are keyed in remotely. If a wrong key is touched, it resets the lock. The lock code can be set by connectiong the line wires to the pads A, B, C and D in the figure. For example, if the code is 1756, connect line 1 to A, line 7 to B, line 5 to C, line 6 to D and rest of the lines-2,3,4,8 and 9 to the reset pad as shown by dotted lines in the schematic.

    Schematic of the code lock circuit

    code lock circuit schematic

    The code lock circuit is built around two CD4013 dual-D flip-flop ICs. The clock pins of the four flip-flops are connected to A, B, C and D pads. The correct code sequence for energisation of relay RL1 is realised by clocking points A, B, C and D in that order. The five remaining switches are connected to reset pad which resets all the flip-flops. Touching the key pad switch A/B/C/D briefly pulls the clock input pin high and the state of flip-flop is altered. The Q output pin of each flip-flop is wired to D input pin of the next flip-flop while D pin of the first flip-flop is grounded.

    If correct clocking sequence is followed then low level appears at Q2 output of IC2 which energises the relay through relay driver transistor T1. The reset keys are wired to set pins 6 to 8 of each IC. (Power-on-reset capacitor C1 has been added at EFY during testing as the state of Q output is indeterminate during switching on operation.)

    This simple code lock circuit can be usefully employed in cars so that the car can start only when the correct code sequence is keyed in via the key pad. The code lock design can also be used in various othee application.

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    37 Responses to "Simple Code Lock Circuit"

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    1. more notes can be given with function description

    2. ricky morco says: on December 15, 2009 at 2:45 am

      pls i need parts list.

    3. i need the operation of above elements

    4. Nikita jain says: on April 11, 2010 at 11:02 am

      i m working on the project mobile bug.so, plz, send me the layout of mobile bug on my mail addres.

    5. priyanka says: on June 26, 2010 at 1:07 pm

      plz, send me complete info abt simple code lock

    6. stremeni4 says: on May 24, 2011 at 11:09 am

      can you send me e pcb? please!

    7. plz give me more information & notes about electronic lock……….

    8. can your circuit be programmed in terms that the password could be reset?? Thnx :D

    9. Tahir Khan says: on October 7, 2011 at 5:29 am

      please tell me about part list…and can i attached LCD with this?if yes then how?

    10. chandrika k b says: on October 27, 2011 at 11:46 am

      i have made the circuit but i need the idea how to check its proper operation i.e how this code is taken by an encoder and help in accessing its application

    11. saravanan says: on January 3, 2012 at 5:41 pm

      c1 and c2 increase the value of capacitor for better result….

    12. sir please give more notes and description on this topic

    13. how does this circuit works?? and i want more applications….please send as soon as possible

    14. could you mail me a parts list for this please?

      many thanks

    15. sir..plz plz give more discription about ths ckt.
      Send me the working .
      I want to knw all abt ths ckt..
      As soon as possible

    16. i am working in this project please send me more description in my mail. thanks

    17. plz send me more detail of project.

    18. PLZ GIVE ME FULL INFO OR DISCRIPTION OF THIS PROJECT

    19. can this be done with a 74ls373 while pressing the wrong button the latch is turned on!

    20. Cn u send m the pcb layout and more info .about the simple code lock circuit

    21. .Plz response to my comment quickly ………hi nid pcb layout of dis circuits

    22. IS this circuit taking care of Debounsing effect

    23. vigneshdrv says: on February 6, 2013 at 12:03 pm

      please send the working process of the ckt to my mail id
      and also the switching sequence please

    24. we need operation of the above circuit it is not working

    25. heyy guyzz i want this code lock by using 4 ICs that 4013 so can i get diagram ??

    26. please send me the detailed info of the circuit to my mail id.

    27. plz send me detailed info of the circuit to my mail id.

    28. how can i implement this poject practically plz rply

    29. can you please send me more detailed information of the circuit? I really need this for our project. and also send the working process of the circuit to my mail id
      and the switching sequence please. thank you.

    30. DAUDI DITTO says: on October 23, 2013 at 1:40 am

      i am working on this project can yu please send me more information and more details.ASAP

    31. Peter mainza says: on March 27, 2014 at 5:33 pm

      Am done with this project only how to write a report help

    32. I am working on this project,please give me clear details about working of this project.

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