@jacmika it would need shell escaping and it is missing the initial D. I would try something like --extra-cxxflags="-DMY_RF24_BASE_RADIO_ID=0x00,0xFC,0xE1,0xA8,0xA8 If I recall correctly, the output of make will show which defines are activated, and what values they have. That's what I usually use to check if I got it right.