I spent a several days ( 12-15 hrs ++) trying to get a WTV020-SD-16P to work as a standalone sound player, just as a test for my project. It did finally work as a standalone. If I can do it, so can you, from this test setup, the experience can be built on. I used a buck power supply ( cost less than $2 ) to get the 3.3 V from a 5v power supply ( the 5V power supply is a cell phone charger ).
Some really good information is scattered in the forum, so I started a post here just for listing best practices and troubleshooting tips.
My big problem: Wired very simply as shown, MP3 mode, when the play was triggered by connecting pin 9 to ground, all that came out was a feeble 1/2 sec beep. It didnt matter if the SD card was blank or had files on it. Root problem was the micro-SD memory card. It worked fine connected to my PC thru a card reader. The needed advice, not found in vendor documentation, is: " Before the memory card can be used it must first be formatted with FAT16 option."
After reformatting the memory card, copied sample .ad4 files to the card & voila ! success ! http://www.4dsystems.com.au/prod.php?id=73. I'd thought the files would be limited to 20 seconds, these sample ad4s seem to be alot longer than that.
I also wired pin 2 [DAC +] up to a 15W amp to drive a car speaker. There is a loud POP when the sound files starts and stops, not sure of a DC blocking capacitor will fix that. Any suggestions ?
P.S. the LED goes out when pin 15 "BUSY" output goes high, so the LED really should be labeled "Not Busy". After the aggravation of getting started is over, this inexpensive module looks to have alot of capability and uses for many fun hobby projects.