While testing a slight modification on the PU-2 prototype, I decided to test the current draw of the SD Card reader described in the previous post. I placed my multimeter in series with the 3.3 volt pin and measured 11 milli-Ampères. Even while reading data, the current draw was constant. I then decided to measure the current draw when using 5 Volts. I disconnected the 3.3v pin and connected the 5v pin in series, again, with the multimeter. The current draw was 0 mA. !?
I disconnected the 5v pin and launched the reading program on the Arduino. It works. Really! The SD card reader is linked to ground, and MISO, MOSI, SCK and CS pins. NO power.
I can only guess that the SPI pins provide the necessary power to read the SD card. Here’s the schematic for this particular adapter:
Anyone has any idea? Anyone wants to try and replicate this?