Three switch Analogy

Now when we already know how to design a control logic for a 2 switch input let us proceed further now taking 3 input switches and solving some questions on them;

Ex 1:- Given three switches I₁, I₂, I₃ to control the O/P, it is mandatory that all the three switches are pressed together to activate the O/P.

I1	I2	I3	O/P
0	0	0	0
0	0	1	0
0	1	0	0
0	1	1	0
1	0	0	0
1	0	1	0
1	1	0	0
1	1	1	1

Let us check out the question first so that we can pull out a truth table from it which will tell us that on what condition of the switches the output was ON or the relay coil was ON.

Just like a general truth table we put the inputs on one side and output on another one.

Each input will have only two conditions but when connected to each other that might raise upto 8

Now keeping in mind,

1     =  pressed

 0  =  released (no action)

We need to find out on which situation the output turn ON(high).

Recalling the question we find out a specific line “all the three switches are pressed together to activate the O/P” that verifies that the output will turn ON when all the switches (inputs) are pressed(1).

1

1

1

1

Hence forth the output will turn on when    I1 = 1,     I2 = 1, and I3 = 1.

Checking out the status of the switches and will give us there types and as the situation in which the output turns ON is when   I1 is pressed(1) and  I2 is pressed(1), and I3 is pressed(1), it provides us the relation between the inputs. i.e. AND gate.  Hence forth the Boolean equation can be deduced, i.e.

I1 . I2 . I3 = O/P

Now let’s pen down the relay logic diagram for the given Boolean equation that is easy just keep in mind the simple logics that we have created.