‘char’ variables can be -128 to 127, you don’t need a negative in your case.
‘byte’ variables can be 0 to 255 .
Both are one byte of storage.
Get into the habit of selelecting the appropriate ‘type’ necessary for your variables.
Wawa is using ‘const byte’, const say this is a constant which will not change.
The compiler reserves no memory for constants.
If you want to maintain the isolation on the relay board, follow the suggested wiring changes.
Here is an 8 relay, similar, board and the suggested wiring:
