# BCD to 7 segment display

Discussion in 'Homework Help' started by diamondking3, Apr 10, 2011.

1. ### diamondking3 Thread Starter New Member

Mar 16, 2011
14
0
Hi there, I'm kind of stuck with how to figure out the logic circuit using Boolean expression.

My question is:
for the first logic circuit, use the un-simplified boolean expression from the fundamental truth table. use multisim to confirm the logic operation. explain the state of the 7 output LEDs for all the comination of the 4 input switches.

I've done the truth table and now don't really know what to do next...

2. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
Post it here.....

3. ### JDT Well-Known Member

Feb 12, 2009
658
85
From your truth table (if you have done it correctly) you should be able to produce a logic equation for each segment. Simplify these equations.

Mar 16, 2011
14
0
5. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
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6. ### diamondking3 Thread Starter New Member

Mar 16, 2011
14
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Thank you debjit625!
But.... i'm still kind of confused....
Could you please do an example?

7. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
You could get the data sheet for a CD4510 and see how that works. The process is pretty straightforward, though. For each input in the table, the output has to enable the correct segments in the display.

Thee are only 7 segments, so the logic is not quite endless.

8. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
Ok I will show you an example for the "a" output,here in the truth table the output goes low only two times first when (A = 1,B = 0,C = 0,D = 0) and second time when (A = 0,B = 0,C = 1,D = 0) so if we find the product of sum for this we will get

Output = (A' + B + C + D) (A + B + C' + D)

The circuit will be some thing like this

If you still dont get it you can try our ebook a bit further

Good Luck

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9. ### diamondking3 Thread Starter New Member

Mar 16, 2011
14
0
OK, Thanks! Don't worry, i've got it now.
BUT... hehe..... (sorry to bother u)
theres another question...
How do i create a circuit using BCD Counters (i suppose its 4510) and make it count to the value of 27 using teo seven segement displays. (so that means i have to make a segment from 00 to 27)

10. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
For that you need two BCD counters (like 7490 or 4510) and two BCD to seven segment decoder/driver (like 7447 or 4511).

Note like 7490 and 7447 , 4511 decoder is a complementary IC to the 4510 counter so when using 4510 use 4511 for the decoder.

Good Luck

Apr 15, 2011
2
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12. ### diamondking3 Thread Starter New Member

Mar 16, 2011
14
0
Cool, Thanks Guy!
Just wondering how do i make it automatic???
How to switch the 1 segment display on then wait till it turns to 9 and the other segment display turns on..... showing 2 digit number???

13. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
Let's look at the logic behind your inquiry. You want a segment to be deactivated until the previous segment reaches 9. Then it should behave normally.

In order to recognize the "9", you can build a standard boolean logic function. I presume you know how to do it.
Next you must store that output somewhere. A D-Flip Flop is ideal. Since you want the information about the appearance of the "9" to be permanent, you must loop the output of the DFF back to its input in order to constantly feed it the HIGH, once it has appeared once.

Now that you have the acknowledgment signal, you must decide what you can do with it.
At first I thought of the LE Enable input of the 4511, but then I noticed that the output isn't stictly defined by it. So I thought about using a 8-to-4 MUX. When the FF output is 0, the MUX will give 1111 to the 4511, making it display a blank screen. When the FF output is 1, the 4511 should be given its normal input.

Is that clear?

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