Can anyone help me clean up this layout

Thread Starter

mnunez021

Joined Feb 27, 2009
18
When I test this layout everything works fine except the decimal. The decimal has to work by itself but when I turn it on, other parts turn on also
 

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SgtWookie

Joined Jul 17, 2007
22,220
I replied to your post in the Homework Help forum.

Sorry it takes awhile; this forum isn't interactive and I have several things going on.
 

Audioguru

Joined Dec 20, 2007
11,249
This site is asleep.
It takes many minutes for the attachement to load. It takes many minutes for my reply to work.
The attachment is not a schematic. It is a fuzzy JPG file type that is covered with chicken-pox dots.
 

beenthere

Joined Apr 20, 2004
15,819
It shows no voltage pin to the 7 segment display, nor does the logic have current limiting resistors. I question the working part.
 

SgtWookie

Joined Jul 17, 2007
22,220
It shows no voltage pin to the 7 segment display, nor does the logic have current limiting resistors. I question the working part.
I was wondering about those same issues.
So, I downloaded Logisim, available for free here:
http://sourceforge.net/projects/circuit
No limitations.

The quirky thing about the library 7-segment display is that it's common-cathode (and automatically "grounded"), whereas most 7-segment display drivers are common-anode.
It also appears to have a "built in" current limiting circuit; just supply a logic '1' to a segment, and it lights up.
 

SgtWookie

Joined Jul 17, 2007
22,220
Is the decimal point being turned on by I3 only?
No, it's supposed to be turned on if the input is not a valid BCD number.

DecimalPoint = I3 AND (I2 OR I1).

They need some additional logic to accomplish what they need to do; if the input is not a valid BCD number, then none of the segments should be lit except for the decimal point.
 

mik3

Joined Feb 4, 2008
4,843
He has to check his truth table and his connections carefully.


Decimal point=I3 I2' I1 I0' + I3 I2' I1 I0 + I3 I2 I1' I0' + I3 I2 I1' I0 +
I3 I2 I1 I0' + I3 I2 I1 I0
 

mik3

Joined Feb 4, 2008
4,843
Your truth table is not very helpful for you.

Put each signal for each segment of the display on the table and derive boolean equations according to the table.
 
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