# DOB seven segment display

Discussion in 'Homework Help' started by axel1111, Apr 20, 2011.

1. ### axel1111 Thread Starter New Member

Apr 20, 2011
2
0
iam getting confused on this problem in my homework in which all you have to do is display your DOB on 1 seven segment display by cycleing through them with three switches in binary. I am getting stuck at where it says "write the simplified Sum-Of-Products Boolean equations forthe seven outputs a, b, c, d, e, f, & g."

My truth table is here:http://pastebin.com/UuKatSvZ

(using pastebin so everything is still inline)

so my question is how would i write out the SOP equation for a,b,c,d,e,f & g?

2. ### Georacer Moderator

Nov 25, 2009
5,154
1,281
Actually, you need 7 Boolean functions, one for each segment of the 7-segment display. Each function will correspond to a logic circuit that will read the three inputs and drive only one segment.

Do you know how to construct a Boolean function from a truth table through a Karnaugh map? Check here if the answer is no: http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Logic/Logic3.html

3. ### axel1111 Thread Starter New Member

Apr 20, 2011
2
0
i know how to make a boolean expression from a kmap but this one doesnt make any sense to me

4. ### Georacer Moderator

Nov 25, 2009
5,154
1,281
Ok, let's describe it in a different way:

We know that the 7-seg display must show a predefined symbol for each different combination of its 3-bit input.
We 'll take it a bit further and say that each separate segment must be either ON or OFF for each of the 8 different inputs. Isn't that a standart boolean function that takes the value 0 or 1 depending on 3 input variables X, Y and Z?
And since we have 7 segment, we have 7 boolean functions in our hands.
For each function, a digital circuit must be built in order to drive the respective segment.

I 'll give you the example of the "a" segment, based on your image attachment:
Let the function A represent the boolean function that will describe the operation of the "a" segment.
A(X,Y,Z)=Σ(2,5).
After the simplification (which in this case is non-existent), that becomes:
A=X'YZ'+XY'Z.
That is the function which after being implemented into a circuit, will drive the "a" segment.

Is that clear?