I want to use a Catalex Micro SD Card Adapter in Combination with my Arduino MKR GSM 1400. The problem is, that the Arduino uses 3.3V to operate but the SD Adapter needs 5V (or at least 4.5V) to operate properly. Can I just use the 5V output of my Arduino to power the adapter, or will a higher voltage destroy the arduino when using it over a longer period of time? And if so, how can I use my MKR GSM 1400 with a SD-module? Maybe by unsing a step up/down converter in my circuit or just switch to a module that uses 3.3V?


Catalex Micro SD Card Adapter has built-in level converter in a form of 74ABT125 3-state buffer. This buffer chip needs 4.5 to 5.5V voltage supply (recommended values) This is why you would need +5V from your Arduino to the adapter.
Link to 74ABT125
Link to Catalex Adapter schematic

To operate Adapter you would need a certain logic level. Your Arduino provides signals with 3.3V level. The question is: Is it enough? Let's see the datasheet: enter image description here The answer is yes, you can connect your Catalex SD card adapter with your Arduino.
Good luck

There is a concern regarding MISO line voltage levels. MISO signal is the one from 74ABT125 to Arduino. Look at the schematic below: Catalex Again, looking into 74ABT125 datasheet (High level output voltage):
enter image description here
Looking at this datasheet, it shouldn't be a problem. Anyway, you can add a resistor divider in MISO line to mitigate the problems.

Note: SAM microcontroller used in your Arduino can accept Vdd + 0.6V on the PIN (maximum rating) making 3.3V + 0.6V = 3.9V

enter image description here

  • So how should I wire it? Just connect to SD-VCC with the 5V output of the Arduino . And put both ground pins together and the arduino won't be affected by this higher voltage because on all the other pins (cs,mosi,miso and sck) it will send all the data with 2V high an 0.8V low? So nothing over 3.3V wich would harm this arduino? – Cowboy_Patrick Aug 30 '18 at 8:09

The SD card is a 3.3 V device. The 5 V module with SD card adapter steps down the voltage for powering the card and has logic level conversion for card's SPI pins.

If you want to connect SD card to a 3.3 V board it is better to use a simple breakout board without power and signal conversion.

I do not recommend you to connect a 5 V SPI device to MKR SPI pins without logic level conversion.

EDIT: smajli analyzed in his answer the logic level conversion chip used on the adapter you use. it doesn't output more than 3.3 V and you can use it powered from 5 V. but it is still a workaround.

  • why is it a workaround if it has even bulit in such a chip? so can i use it safely and no 3.3v electronics can get damaged? of course if the wiring is right – Cowboy_Patrick Aug 30 '18 at 11:21
  • it is a workaround because the voltage conversion is obsolete. you should us an adapter without conversion. – Juraj Aug 30 '18 at 12:00
  • ok, thanks i'll buy a 3.3V sd adapter – Cowboy_Patrick Aug 30 '18 at 12:18

I have seen in several Catalex schematics that show pin 13 of the 74ABT125 is connected directly to GND. This would be correct?

Catalex schematic

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