Digital Keypad Combination Lock


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This simple circuit is the electronic version of the combination lock. Using the special purpose LS7220 digital lock IC, the circuit allows a 4 digit combination of your choice to activate a relay for a set period of time. This relay can then be used to trigger a lock solenoid, enable a starter button, open a motorized door, or many other tasks that require a momentary signal.

Schematic

Schematic for combination lock

Parts

Part
Total Qty.
Description
Substitutions
C111uF 25V Electrolytic Capacitor
C21220uF 25V Electrolytic Capacitor
R112.2K 1/4W Resistor
Q112N3904 NPN Transistor2N2222
D111N4148 Rectifier Diode1N4001-1N4007
K1112V SPDT RelayAny appropriate relay with 12V coil
U11LS7220 Digital Lock IC
S1-S1212SPST Momentary PushbuttonKeypad (see notes)
HD1112 Position Header

Notes

  1. To set the combination, wire the appropriate switches to U1 pins 3, 4, 5 and 6 using the header. For example if S1 was connected to pin 3, S2 to pin 4, S3 to pin 5 and S4 to pin 6, the combination would be 1,2,3,4. Now wire all other unused switches across the header to pin 2 of U1. In this way you can create any 4 digit combination you want. Pin 2 is the reset pin, so connecting all unused keys to it assures that the entire combination must be reentered if an incorrect key is pressed.
  2. When the appropriate combination is entered, the relay is activated for a period of time determined by C1. The 1uF capacitor specified in the parts list will result in an on-time of roughly 5 seconds. Increase the value of C1 to increase this time.
  3. An easy way to make a keypad is to buy 12 PC board mount pushbuttons and then etch a PC board so that the buttons are in 4 rows of 3, similar to a telephone keypad. Place this in a case and then use a label maker or transfer letters to add your numbers to the tops of the pushbuttons. You can also use a pre made keypad but keep in mind that you need a pad which provides an output for each key. Most pads available have the keys connected to provide a row and column signal when they are pressed.

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Comments

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Mike
Digital Keypad Combination Lock
Sunday, September 29, 2013 12:02:01 PM
If i was to put a switch and jumper cable before C1, will this allow me to keep the relay active permanently when the switch is set to bypass (valet mode)? I basically want to have a set up where i punch the code in as normal to activate the relay then after X number of seconds the relay will deactivate Then at certain times like for car servicing i want to punch the code in and keep the relay active permanently so i dont have to give the code to the service manager? hope you can under stand where i am coming from? C|heers, Mike.
pervez
Digital Keypad Combination Lock
Tuesday, March 13, 2012 8:50:08 PM
I am new and 1st year 2nd semester. My course teacher give a project of electronic lock. Please somebody help me giving a helpful link. or help me via Facebook. search me at afsarpervez@gmail.com Please help me . I have got only 20 days to complete this project.
rituraj chouhan
Digital Keypad Combination Lock
Sunday, September 06, 2009 2:09:10 AM
its nice for major project
catprog
Digital Keypad Combination Lock
Tuesday, June 23, 2009 6:03:47 AM
you can do something similar by connecting the 1st button to the s pin of a SR flip flop. Take the Q output and use an AND gate to combine it with the next button and run the output to another S pin. then using the Q bar outputs use not or nor gates to get a number of high outputs which you can AND together
Patrick
Digital Keypad Combination Lock
Friday, April 10, 2009 1:19:09 PM
They can also be found on ebay for a reasonable price. There is a kit there that does something similar to this
SAN
Digital Keypad Combination Lock
Friday, March 27, 2009 8:05:25 AM
I cant get the LS7220 in any of the shops in kolkata .can you plz suggest an alternate chip for the circuit?
anonymous
Digital Keypad Combination Lock
Sunday, February 15, 2009 12:04:39 AM
how do i connect my keypad together with an lcd to display the code
john ng'ang'a ngugi
Digital Keypad Combination Lock
Thursday, January 22, 2009 3:20:29 AM
can i get less expensive alternative components to enable a student present the project to the market?bearing in mind the student is not earning but al for expertise.
HappyMan
Digital Keypad Combination Lock
Thursday, January 15, 2009 12:26:47 PM
http://www.abra-electronics.com/products/product.php?productid=1395&cat=0&page=1 The parts is sold there..... but expensive..... > $19
anonymous
Digital Keypad Combination Lock
Tuesday, November 04, 2008 8:24:32 AM
how do i connect my keypad together with an lcd to display the code
ielle
Digital Keypad Combination Lock
Tuesday, August 12, 2008 5:52:57 AM
i just want to ask, where do you buy a sample of the LS7220 Digital Lock IC chip.
RJL
Digital Keypad Combination Lock
Tuesday, May 06, 2008 11:48:34 AM
is there any substitute for LS7220 ?
anonymous Mario Maciel
Digital Keypad Combination Lock
Thursday, April 17, 2008 7:14:09 AM
I buy keypads perfect for this application...... 1 common + and 1 signal for each key. copy and paste to go to: http://www.allelectronics.com/cgi-bin/item/KP-12/300/12_BUTTON_KEYPAD_.html
farhad gul
Digital Keypad Combination Lock
Wednesday, March 26, 2008 7:23:24 AM
Sir,where could i get LS7220 Digital Lock IC..i had tried for it for more than enough shop but i cant got.plzzzzzzzzzzzzzzz rep me
Raj
Where could i get LS7220 Digital Lock IC
Wednesday, February 27, 2008 3:32:16 AM
Where could i get LS7220 Digital Lock IC..i had tried for it for more than twenty five shops..plz send an alternate or send me the an alternate ic to be used in that place.. Regards rajkumar..
Ramzi .B
Digital Keypad Combination Lock
Friday, January 25, 2008 5:31:06 AM
Hi. I'm just asking if u can brovide me with another circuit for the electronic door key lock. And that would be kind!

(Editor's notes: What's wrong with this one?)

Hessam Siddiqui
Digital Keypad Combination Lock
Thursday, January 10, 2008 6:15:26 PM
Hello. I just would like to know were you can buy or order a sample of the LS7220 Digital Lock IC chip.
Alok D
Flash Trigger
Tuesday, January 01, 2008 3:14:00 AM
Respected Sir, I need a circuit for momentarily triggering a Flash used in a standard Film Camera. Thanks and Regards, Alok D
mayur
Digital Keypad Combination Lock
Sunday, December 09, 2007 9:59:48 AM
can you give the real image of Digital Keypad Combination Lock
Kevin
Digital Keypad Combination Lock
Wednesday, November 07, 2007 8:45:57 PM
Where do you buy LS7220?
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