# Problem/idea with flip flop circuit

Discussion in 'Homework Help' started by wildan03, May 19, 2012.

1. ### wildan03 Thread Starter New Member

May 19, 2012
2
0
Im currently trying to modified a simple car alarm system (using flip flop ) as shown in the figure below

the above system will trigger and alarm if either the door (D) or any vibration (V) occur to the car and by using flip flop it will remain the alarm on even if the door or the vibration stop.

So what i wanna change here is i want to make it a password safety system. It will compare D and V value if same will let the user login but if wrong for 3 times, user can never login even if the next password entered is correct. So anyone? how do i make it for the flip flop gives a value of 0 for the 1st try, 0 for the 2nd try but 1 for the 3rd try? do i have to use 2 flip flop?

2. ### MrChips Moderator

Oct 2, 2009
18,330
5,793
You need a counter to count from 0 to 3. Hence you will need another pair of flip-flops, three would be better.

Since you can use four flip-flops altogether, why not use two dual flip-flip ICs.

3. ### wildan03 Thread Starter New Member

May 19, 2012
2
0
thx for the reply, unfortunately my project only allow me to use simple JK flip flop, cannot use IC, can sugest any useful link for reference purpose? =(

4. ### MrChips Moderator

Oct 2, 2009
18,330
5,793
The circuit you showed is not a J-K flip-flop. That is an R-S flip-flop.

What do you mean by IC? They are all ICs.

So what is wrong with using four J-K filp-flops?