hi friends, i used one rc522 and one sdcard module. according to thread you adviced i used 4148 diodes between modules and arduino. only sd card module run. if i took off vcc wire from sd card module , rc522 run. and also took off rc522 vcc wire in this case sd card run. but at the same time that wires connected ,only sd card module run. and also i used 330r resistance instead of diodes , the result same .
so please give me some advice why? we can use a lot of spi modules. give me same electronical knowledge about this kind of problem.