Arduino: Formula to convert byte

Question

Im looking for a way to modify a binary byte value on Arduino.

Because of the Hardware, its neccesarry, to split a two digit number into 2 4-bit.

the code to set output is wire.write(byte, 0xFF) which sets all outputs on High.

0xFF = binary 1111 1111

the formula should be convert a value like this:

e.g nr 35 is binary 0010 0011

but for my use it should displayed as 0011 0101 which would be refer to 53 in reality.

The first 4 bits are for a BCD-Input IC which displays the 5 from 35, the second 4 bits are for a BCD-Input IC which displays the 3 from 35.

Does anybody has a idea how to convert this by code, or like a mathematical formula? Possible numbers are from 00 to 59.

Thank you for your help

So you want to split the numbers up, convert them and 'glue' them back together again... — Beta Decay
– Beta Decay, Commented Aug 3, 2014 at 15:53

Scott Hunter · Accepted Answer · 2014-08-03 18:16:48Z

1

To convert a value n between 0 and 99 to BCD:

((n / 10) * 16) + (n % 10)

assuming n is an integer and thus / is doing integer division; also assumes this will be stored in an unsigned byte.

(If this is not producing the desired result, please either explain how it is incorrect for the example given, or provide a different example for which it is incorrect.)

edited Aug 3, 2014 at 18:16

answered Aug 3, 2014 at 14:37

Scott Hunter

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3 Comments

sgtBear Over a year ago

i dont want to convert to bcd! i have to adjust the byte! My port expander has 8 Outputs, and you only can adress the whole byte! its about assemble 2 4-bit bytes to an single 8 one.

cup Over a year ago

Do you mean you want the first byte to be (n/10) and the second one to be (n%10) or do you want them both in the same byte? If you want them both in the same byte then it is the BCD conversion the @Scott Hunter has given.

sgtBear Over a year ago

cup the byte is 0000 0000, the first 4 0 should contain digit 1, and the second 4 0 should contain digit 2

Beta Decay · Accepted Answer · 2014-08-03 16:09:04Z

#include <string.h> int num = // Any number from 0 to 59 int tens = num/10; int units = num-(tens*10); // Make string array for binary string tensbinary; int quotient = tens; char buffer[1]; // Convert numbers for (int i = 0; i < 4; i++) { quotientint = quotientint % 2; sprintf(buffer, 1, "%d", quotientint); binary.append(buffer); } // Repeat above for the units // Now join the two together binarytens.append(binaryunits);

I don't know if this will work, but still, you might be able to extrapolate based on the available information in my code.

The last thing you need to do is convert the string to binary.

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