Can add two Hexadecimal digits to give sum upto only 1 digit, upto 15 (f).
The input is in the form of binary representation of the digits. You can find the number you want to give input via this table->
0000 -0
0001 -1
0010-2
0011-3
0100-4
0101-5
0110-6
0111-7
1000-8
1001-9
1010-A(10)
1011-b(11)
1100-C(12)
1101-d(13)
1110-E(14)
1111-F(15)
Give input via the 8 switches on the top if the circuit and you will get the algebric sum of the digits. Hope you can make it better.
