Security Alarm system

Thread Starter


Joined Dec 8, 2006
Hello everyone.
I am doing my final project for DLD ( Digital Logic Design ). I have to make a security alarm system..the user will input a password, if it matches with the one saved in register,the light will turn on otherwise if both the passwords don't match,it won't turn on.

Kindly someone send me a circuit diagram for it. I need it urgently.


Joined Mar 3, 2007
ok using DLD is not flexible if you want to change the password even you change the wiring for the circuit
but you can do this simply by th following if you want three digits password let them a,b and c let input b tb be inverted by inverter then use and gate with inputs A and B' use to get x another and gate with input x and C to get the out put Y then Y won't be true unless the entered value 101 so the password is 101


Joined May 16, 2005
I would use exclusive OR gates. Put the compliment of the password on one set of leads (can be set with dip switches). Put the password itself on the other set of leads (probably from a shift register.) AND the outputs together. Done.