For my project i need a bunch of arduinos to log a few readings per second to an SD card. Absolute reliability is not that important since i have redundancy.
So i got these super cheap SD card modules from china:
Yeah, yeah, ive heard all about how these things dont properly convert the logic signals and can damage the cards... but ive also heard plenty of people getting them to work. I also got some super cheap 256 mb sd cards from china which i dont care that much about destroying.
I uploaded this logging sketch: http://profmason.com/?p=1956
and the card either corrupts or the file is created and nothing is actually saved to the file. HOWEVER, when i wire the arduino 3v3 directly to the sd module 3v3 (bypassing the onboard reg) it magically works. Upon measuring the voltages coming out of the SD module's onboard reg (powered by the 5v arduino reg), i read 3.1v. Is that low enough to cause the SD card to not work properly? And does the arduino have sufficient power to run an SD card off its 3v3 reg if nothing else external is using that rail?