Measure the mA it draws at 3.6v and use a resistor to drop the remaining 1.4v at that measurement from the 5v out of the board. Cheap and easy, of course at the price of efficiency.
Ok, 2 diodes in series?
Hello...I've just bought a couple of these, not knowing what problems were waiting for me. I've just been fighting with them for a couple of hours and basically had every problem described in these forums. I think the real problem comes down to power supply.a) SD cards need up to 3.6V to operate - more than the Arduino 3.3V pin can supply.b) SD cards need a surprising amount of current to work. Add to this that you're also trying to drive a 4W speaker (or whatever) and you'll soon overwhelm a little voltage regulator.The voltage/current needed by a card obviously varies between cards which is why some cards work better than others. Using an external amplifier probably helps a lot, too.In my case I was getting nothing at all with the Arduino 3.3V supply. I tried the "two diodes" trick and got sound, but the files only played for a couple of seconds before stopping. I looked at the voltage and it was going up and down wildly. There was usually a drop down to about 3V when the sounds stopped playing (probably low enough to give SD card errors...)As a test, I tried using a 3xAAA battery pack, and ... bingo! Everything started working perfectly. The batteries were putting out about 3.8V and not drooping too much when things got busy.Bottom line: I think you need a fairly beefy 3.6V supply to run this thing properly (or a reasonably good 3.6V supply plus an external amplifier).