[sdiy] binary to two 7 segment display thingy..

[René Schmitz]

Hi Nils and all,

nice solution!

I think it can be simplified even further, comparing against less or 
equal 7 means just that bit 3 must be 0, so you can use that directly to 
control the B2 and B3 inputs of the adder.

Cheers,
  René

nils wrote:
> Someone asked about that some hours ago, how to converting 4-bit numbers to two 
> bcd's from 01 to16.
> 
> That was a nice puzzle. How to do it with few and cheap standard parts? Here is 
> the solution I came up with.
> 
> I just use a 4bit adder and a 4 bit comparator. Outputs are two BCD's ready to 
> be feed into a decoder chip.
> 
> The trick is to take the binary input and compare it against 8. If  the number 
> is lower or equal to 7 I just add one (for the numbers 1 to 9), otherwise I'll 
> add 7. The overflow inside the adder will signal numbers higher than 9 on the 
> carry output and adjust the adder sum to be between 0 and 6 again. It doesn't 
> even need any gluelogic :)
> 
> I haven't simulated it though, if you want to use it you'll better check it..
> 
>   Bye,
>     Nils
> 
>                                         74HC283
>                                         +-------+
>            >------+---------------------|A0   S0|------>
>     binary >-----+|---------------------|A1   S1|------> to low digit
>     input  >----+||---------------------|A2   S2|------> bcd->7segment decoder
>            >---+|||---------------------|A3   S3|------>
>                ||||                  1--|B0     |
>                ||||              +------|B1   C0|---0
>                ||||              +------|B2     |
>                ||||  74HC85      |   0--|B3   C1|------>
>                |||| +-------+    |      +-------+  0---> to high digit
>                |||+-|A0  A<B|    |                 0---> bcd->7segment decoder
>                ||+--|A1  A=B|    |                 0--->
>                |+---|A2  A>B|----+
>                +----|A3     |    
>                  0--|B0    2|--0 
>                  0--|B1    3|--1 
>                  0--|B2    4|--0
>                  1--|B3     |
>                     +-------+
> 
> 

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159






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