08-05-2012, 10:42 AM
PASSWORD DETECTOR
PROBLEM STATEMENT (2).docx (Size: 324.22 KB / Downloads: 49)
PROBLEM STATEMENT
Design a circuit that takes an input code from user and checks if the entered code is same as the password set and if so indicates it.
HARDWARE USED TO DESIGN THE CIRCUIT 1
AND gate ICs
D-FLIP FLOP ICs
Diodes
Resistors
Push buttons
A voltage source
Transistor
WORKING OF CIRCUIT 1
In the circuit shown, A, B, C, D, RE are inputs. S represents the preset, R represents the reset, CLK represents the clock of the D FLIP-FLOPS. The inputs are in the form of pulses.
The circuit responds only to the right sequence of four digits that are keyed in remotely. If a wrong key is touched, it resets the flip flops. The password can be set by connecting the input 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-0,2,3,4,8 and 9 to RE.
When the key 1 is pressed the first flip-flop sets and the output Q of the flip-flop becomes 1 and Q’ becomes 0. When the key 7 is pressed the second flip-flop sets and the output Q of the flip-flop becomes 1 and Q’ becomes 0.similarly When the key 5 and then the key 6 is pressed the third and fourth flip-flop sets and the output Q of the flip-flops becomes 1 and Q’ becomes 0. For all other combinations the flip-flops resets.
Hence this circuit successfully detects if the entered code is the right password or not.
HARDWARE USED TO DESIGN THE CIRCUIT 2
D-FLIP FLOP ICs
Resistors
Push buttons
A voltage source
Transistor
WORKING OF CIRCUIT 2
This is a simple but effective code lock circuit that has an automatic reset facility. The circuit is made around the dual flip-flop IC 4013.Two 4013 ICs are used here. Push button switches are used for entering the code number. One side of all the push button switches are connected to +12V DC. The remaining end of push buttons 2,3,6,8 is connected to clock input pins of the flip-flops. The remaining end of other push button switches are shorted and connected to the set pin of the flip-flops.
The led will glow only if the code is entered in correct sequence and if there is any variation, the lock will be reset. Here is correct code is 2,3,6,8. When you press 2 the first flip flop(IC1a) will be triggered and the value at the data in (pin9) will be transferred to the Q output (pin13).Since pin 9 is grounded the value is “0” and so the pin 13 becomes low. For the subsequent pressing of the remaining code digits in the correct sequence the “0” will reach the Q output (pin1) of the last flip flop (IC2b).Hence only entering the code in the right sequence makes the LED glow.