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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?

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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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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  • it is a workaround because the voltage conversion is obsolete.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
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You can use the adapter because:

  • the adapter uses an AMS1117 to generate 3.3V to supply the SD card and the level shifter
  • the level shifter is a 74LVC125 which uses 3.3V and works with 3.3V (and accepts up to 5V as input level)

The adapter works for 3.3V and 5V systems as long as 5V power is available.

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Catalex Micro SD Card Adapter has built-in level converter in a form of 74LVC125A 3-state buffer. This buffer chip needs 1.65 to 3.6V voltage supply. The +5V from your Arduino is lowered to 3.3V by the adapter (as seen in the schematics, just change 74ABT125 to 74LVC125A).

Link to 74LVC125A
Link to Catalex Adapter schematic

To operate the adapter you would need a certain logic level. Your Arduino provides signals with 3.3V level. This fits perfectly to the adapter. The answer is yes, you can connect your Catalex SD card adapter with your Arduino.
Good luck

  • 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

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