Pro Mini & SD Card Problems


I currently have a project im working on that consists of a Pro Mini, WaveShare 4.2" e paper display, TinyRTC, RFID reader - RC522 and Micro SD card reader.

Everything is working fine except for the SD card reader. when i plug it in directly to the 3.3v of the pro mini it doesnt work. When i plug it into an external 5v supply, it does but the RFID reader stops working.

Any thoughts on why this is and how can i fix it? link for the SD card reader is here: SD Card Reader

And link for RFID reader: RFID Reader

Is it possible that the SD card reader is sending 5v to the SPI pins causing the RFID reader to not work properly? Is there an easy way to fix or is there any sd card readers that use native 3.3v instead of having a regulator on it?

PS: i tried removing the regular from the sd card reader and jumping the connection to have straight 3.3v go to the cards but it doesnt work either.

Any help is greatly appreciated.


Several things could be going on.

1.) Not enough current for the SD card reader to boot up/work perhaps?

2.) How are things wired? Do the RFID reader and the SD card reader have different CS pins? Are you toggling them correctly? (when you need to use/access either of the devices?

3.) Is the Nano or a +3.3v device? or a +5v device?

4.) If a +5v device... is this SD card reader a shield? Where does the level/logic shifting come into play here?

..cardreader board needs a small fix to release MISO when not selected.
This post shows how. (there is two models shown)