Micro SD card reader question

Thread Starter

Lucky-Luka

Joined Mar 28, 2019
173
Hi all
I have bought a micro SD card reader for an ARduino project.
Micro SD card reader

3.3Vdc or 5Vdc power supply; Communication via SPI.
✅ Compatible with SD Card up to 16GB and SDHC Card up to 16GB; Support SD library.
✅ Through programming, you can read and write to the SD card using your Microcontroller.
✅ Energy consumption module that allows the reading of all the data contained in the SD card, easily interfaced with various types of microcontroller.
✅ This product includes an E-Book which provides useful information on how to start your project. It allows for quick installation and saves time during the setup process. Includes a number of application examples, comprehensive installation guides, and libraries.



I have noticed 2 IC on it:
AMS1117 that is a voltage regulator to have 3.3V on data lines
VHCT125A that should be a buffer
Buffer
Why is this buffer needed? What does it do? I have seen SD cards directly connected to Arduino.
NO buffer connection
Thanks
 
Last edited:

Ian0

Joined Aug 7, 2020
5,097
At a guess it is in the MISO line (Data output from the card), and it allows several devices to be connected to the SPI interface, by making the MISO line high impedance when other devices on the bus are enabled.
If there is only one peripheral connected to the bus, then the buffer is unnecessary.
 

Thread Starter

Lucky-Luka

Joined Mar 28, 2019
173
At a guess it is in the MISO line (Data output from the card), and it allows several devices to be connected to the SPI interface, by making the MISO line high impedance when other devices on the bus are enabled.
If there is only one peripheral connected to the bus, then the buffer is unnecessary.
I have found another possible answer:
https://lastminuteengineers.com/arduino-micro-sd-card-module-tutorial/
There’s also a 74LVC125A chip on the module which converts the interface logic from 3.3V-5V to 3.3V. This is called logic level shifting. That means you can use this board to interact with both 3.3V and 5V microcontrollers like Arduino.
If that is true I wonder how this Chip can understand the voltage of the MISO MOSI pins of my ARduino board.
Moreover if this board would be connected directly to a 3.3V Arduino, this buffer/voltage shifter wouldn't be necessary, right?
 

Ian0

Joined Aug 7, 2020
5,097
SD Cards work at 3.3V, so it could be level-shifting for a 5V microcontroller. A 3.3V microcontroller won't need level-shifting.
It the public has access to the SD card socket then a buffer might protect your microcontroller. You would be amazed how ingenious the public are at making things that are not SD cards fit into SD card sockets.
 
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