Skip to main content

MicroSD Card Module with SPI Connection


A MicroSD card can be directly connected to a 3.3v microcontroller without the need of any additional module. However, a cheap module such as shown in the picture above can be handy in terms of wiring and card replacement. Yet, if you get the module from China then you are on your own, you have to figure it out yourself how the module works.

The module above needs 5v VCC to operate. The 5v is needed by the 3.3v LM1117 regulator to power the MicroSD card and the 74125 bus buffer (the 14-pin IC in the module above). Hence, the bus buffer is operating at 3.3v. The VCC is connected directly to the input of the regulator and no where else. Thus, the VCC is solely meant for the regulator. The right-side SPI bus (CS, SCK, MOSI & MISO) is connected directly to the 3.3v bus buffer. No line in the SPI bus that is connected to the VCC. Thus, the SPI bus does not follow VCC. The buffer is 5v tolerant so the right-side SPI connection can be driven at either 3.3v or 5v. Hence, the SPI can be connected directly to a 3.3v or 5v microcontroller.

However, if your design has only 3.3v power line then you can just connect the input and the output of the regulator together as shown by the green line in the picture above and apply 3.3v to the VCC. That is bypassing the regulator. You may want to remove the regulator all together but not necessary.

The module was designed for 5v operation. The bus buffer is used as a level shifter between a 5v microcontroller and the 3.3v MicroSD card.

You may want to read Connecting a Micro SD Card Adapter to the ESP8266 Development Board.

Comments

Popular posts from this blog

Setting Up PyScripter for Quantum GIS

PyScripter is a general purpose Python Integrated Development Environment (IDE). Quantum GIS (QGIS) is a desktop GIS application that can be extended with Python plugins. Both are open source softwares. We intend to use PyScripter as an IDE to build QGIS Python plugin. We are using PyScripter 2.4.1.0 and QGIS 1.6.0 in Windows. PyScripter does not come with Python. On the other hand, QGIS is built in with Python. Thus, we will setup up PyScripter to use the build in Python in QGIS. We assume both PyScripter and QGIS are already installed. Preparing PyScripter batch file We assume that QGIS is installed in C:\OSGeo4W\ folder and PyScripter is installed in C:\Program Files\PyScripter\ . 1. Copy qgis.bat in C:\OSGeo4W\ bin to pyscripter.bat 2. Edit pyscripter.bat to remove the last line that read something like this start "Quantum GIS" /B "%OSGEO4W_ROOT%"\apps\qgis\bin\qgis.exe %* and replace it with this in one line Start "PyScripter" /B "C:\Progr

Using React in Foundation for Sites

This post was the precursor to the Foundation-React Template . React and Foundation are two different web UI frameworks addressing different needs. They evolve differently. Both of them are powerful on their own accord. Fusing them together may create superpower. We will walk through the process of adding React into Foundation. We will start by installing both Foundation and React through command line interface (CLI). Then we will create a simple Todo web app. Along the way we will highlight the development process. But before all that, let us summarize React and Foundation. The details can be found at their respective websites. Both of them are well documented. React is a run-time UI rendering engine. It renders dynamic UI elements in its own fast virtual DOM, and only update necessary changes to the slow browser DOM. This behaves like a  double buffering DOM which makes any UI update feels fast. React wraps a UI rendering script in a component. A React component can be bound