Binary to ASCII using logical operations
By looking at a ASCII table you can see that the $4$ least significant bits of all characters between $0$ and $9$ correspond to the respective integer representations of the numbers between $0$ and $9$, while the 4 most significant bits are always $0011$ (leading zeroes are not shown in the table, so keep in mind you need to pad binary numbers to 8 bits).

If $x$ is the binary representation of a number between $0$ and $9$, you can then obtain the ASCII representation of the corresponding character as
$$
x \;| \;00110000,
$$

where $|$ denotes a bitwise logical or and the second operand is in binary.