# urgent help plz regarding 7 segment Display!

Discussion in 'The Projects Forum' started by Hasnatsaeed, Dec 11, 2010.

1. ### Hasnatsaeed Thread Starter New Member

Sep 23, 2010
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hi.I have made a fibonacci series generator.now theres a last problem i am stuck at i.e ive used two 4 bit adders to add the two 8 bit numbers.i mean one adder adds the first 4 bits and the other adds the next for bits with carry coming in from the first adder.now the problem is that i want to display this on 7 segment displays.so far ive worked with only one 7 segmet display to display numbers between 0 to 9.ive never used two segments to display 0 to 99 nos but i want to display the series till 99 so how can i connect two 7 segement displays to make this happen?e.g if i add 00000001(1) to 01000000(64), the answer is 01000001 which is 65.. now how can i display 65 on two 7 segment displays?6 on one display and 5 on other display and consequently all numbers between 0 and 99

2. ### beenthere Retired Moderator

Apr 20, 2004
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One problem you are going to face is that the numbers you are working with are binary, and the 7 segment displays are usually made to display BCD values. While you can get displays capable of showing numerals from 0 - 15, most can only do 0 - 9. The displays need a decoder IC in order to work as well.

One possible way to convert from binary to BCD is to load your addition into a string of counters. Clock the value down to zero, while at the same time counting up a string of BCD counters. Clunky, by it works. Or do the math in a microprocessor.

3. ### Hasnatsaeed Thread Starter New Member

Sep 23, 2010
27
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"One possible way to convert from binary to BCD is to load your addition into a string of counters. Clock the value down to zero, while at the same time counting up a string of BCD counters. Clunky, by it works"..i dont understand this.plz explain a little bit

4. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Curious, do you know how to make a BCD counter? A 7490 is a simple version, as is a 4029 (they call it a decade counter, but its real name is Binary Coded Decimal). They even make chips that will take the BCD digits and put them on a 7 segment display such as the 7447 or 4511.

You should now have the information (after you research it) to make a BCD counter yourself. It is pretty basic.

5. ### beenthere Retired Moderator

Apr 20, 2004
15,815
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Do you know that there are different number systems? In you case, you are doing math in Binary. But you need to convert the Binary value to Binary Coded Decimal for the displays.

If you have two Binary counters holding the value 1111 - 1111, you will find that you can't display those values. The largest BCD number is 1001 (that is 9). But, if I have been clever and loaded that count into an Up/Down counter, I can apply a clock and count the value down to zero.

With a string of BCD counters, the same clock, but counting up, when the value in the Binary counters has reached zero, the value in the three BCD counters will be 0010 - 0101 - 0110, and the displays will show 256.

6. ### elementalrage Active Member

Jul 30, 2009
59
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Can you show us what you have - schematic, PCB layout?

7. ### djsfantasi AAC Fanatic!

Apr 11, 2010
2,900
870
Or will they display 255 since that is the decimal value of the bindary number 1111 1111?

Apr 20, 2004
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9. ### n1ist Active Member

Mar 8, 2009
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You can always use a ROM for the decoder; looks like the 74185 is a pre-programmed ROM for doing binary to BCD conversion.

10. ### Hasnatsaeed Thread Starter New Member

Sep 23, 2010
27
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i am sorry but i still dont get this counter thing.i mean if i have a 8 bit number in binary like 01100000 which is 96,should i setup a counter that counts upward and stops until it reaches 96?how?..

11. ### n1ist Active Member

Mar 8, 2009
171
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You have two counters, one a parallel-load binary downcounter, and one a resettable BCD upcounter. Start by loading your binary value into the downcounter and clearing the upcounter. Then clock both until the downcounter hits 0...
/mike

12. ### Hasnatsaeed Thread Starter New Member

Sep 23, 2010
27
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parallel-load binary downcounter, and one a resettable BCD upcounter?..i seriously didnt get you.thanks to my novice knowledge in elctronics..please explain in detail if you can.i mean what are parallel-load binary downcounter, and resettable BCD upcounter and how are you exactly telling me to use them to achieve my goal?.your help is highly appreciated thanks

13. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,842
962
IF you could manage to re type those phrases and words you just posted, into the google search bar, you would find answers to those questions.

14. ### Hasnatsaeed Thread Starter New Member

Sep 23, 2010
27
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ok fine i got it.but whats the theory behind this technique?..i mean how will this work at all?

15. ### SgtWookie Expert

Jul 17, 2007
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The 74x193 is a presettable binary 4-bit up/down counter. You will need two of these.
The 74x192 is a presettable decade (BCD) 4-bit up/down counter. You will need three of these. You could also use a x160 or x162 for the BCD portion.

16. ### Hasnatsaeed Thread Starter New Member

Sep 23, 2010
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thanx.and whats next then?.

17. ### SgtWookie Expert

Jul 17, 2007
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You'll also need to gate the clock from the binary counters' outputs, so that when all of the binary counter outputs are zero, you stop counting up on the BCD counters.

18. ### Hasnatsaeed Thread Starter New Member

Sep 23, 2010
27
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dude your telling me the stuff i should be taking care of when i am half way through it.i am still at zerolevel.where should i start from?.i mean whats the theory behind using these counters to achieve this particular goal?

19. ### blueroomelectronics AAC Fanatic!

Jul 22, 2007
1,758
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Why isn't this in the Homework help section?

20. ### SgtWookie Expert

Jul 17, 2007
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1,728
Arrgh - lost my post.