Hi, it seems that i cant get the rfid MC522 to work after I also connected an SD read/write modul, ordinary amazon uSD including v reg and 5 to 3,3v. The SD is working but not the rfid reader. Its shared SPI bus. Tried different cards and changing cs pin and some different program examples. When measuring the cs pin it seems to allways be about 2,2V, neither low or high... What can be the problem? the program isnt finished just trying to get things working together..
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Have a look at this discussion, sounds like you may have a similar microSD card adapter, the design is very common:
https://forum.arduino.cc/t/spi-sd-card-reader-other-spi-device-not-working-together/447006
Hi, thanks, its seems like that. Just cut off the miso wire from the sd card and then the mc522 jumped working. I will try the fix in the thread so I will be able to use both devices, thanks again 
Hi tried the fix with desoldering pin 13 and connect it directly on the cs pinas in the citat below, but it wont work. Ordered a new sd reader from adafruit, it seems to be build in a slightly other way so I hope that one will work.
The solution was to unsolder buffer pin 13 from the board then solder a wire between pin 13 and the CS input. Then use some hot glue to protect the hair thin wire and solder work. Now when the SD cards CS is high or low the MISO output is high impedance or active.
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