Vermes
Advanced Member level 4
Presented here design is a universal small adapter for microSD memory cards. The main assumption of this project was to create a construction which can be supplied with +5V or +3,3V.
A socket for microSD memory cards was placed on the PCB in a way that the memory card protrudes a little, so it can be easier removed and put back. The system operates with buffer 74LVC125 which provides the possibility to use different supply voltages for cards. Only input lines for cards are buffered: SCK, MOSI and CS. Line MISO in direction to the processor is not buffered. The entire system was tested on both presented voltages and operates correctly even on big values of SPI.
There is also a program possibility to enable/disable the supply for the card itself so that it can be reset if necessary. In addition there is CD (Card Detect) signal derived.
Schematic:
The PCB is very small (29x35mm). It allows mounting on 3mm spacers in the front. In the rear you can direct the headers down or sideways (in the prototype they are directed upwards). If they are directed down, the PCB can be shortened by cutting because in that part there are no paths except the headers.
In a series of headers, next to the PWR pin for supply control, another GND pin was mounted. It was done so that you can connect PWR signal to GND using a jumper, and permanently enable the card supply.
Link to original thread - Adapter microSD - podwójne zasilanie +5V/+3,3V do WAV playera