I recently bought a WTV020 module from eBay, advertised as ‘MP3 VOICE SD CARD VOICE MODULE U-DISK AUDIO PLAYER WTV020-SD’ in one of the ads, in the hope that it would allow me to develop my own SD-card MP3 player using a PIC18/PIC24 micro-controller. Unfortunately, I was in for a disappointment as soon as I read the datasheet…
The module works on 3.3V and has two operating modes. The first is a propietary serial mode where commands are sent via a 2-line (DATA, CLOCK) serial connection. And the second mode is referred to the datasheet as an ‘MP3′ mode, which allows the usage of the module for playback without the need of a micro-controller:
Basically this mode allows the module to be operated directly just by connecting signals to the volume, next/previous, play/pause pins. The module would look up the supported tracks (either WAV or AD4) on the SD card and play them in order. This mode makes the module look like an MP3 player (or so the seller thought), and therefore the item is advertised as an MP3 module! There is actually no support for playback of an MP3-formatted file, as mentioned in the item title. Should I consider this false advertising?
Anyway, after an initial disappoinment, I proceed with testing nevertheless and below are some of my observations:
- Audio playback is via pulse width modulation (PWM), hence the quality is poor. Adequate for low quality voice, but definitely not for music.
- Only small size SD cards (32MB, 64MB, 128MB) seem to work well. Cards with larger capacity (256MB and above) tend to work inconsistently or do not work at all.
- Despite the schematic showing a direct connection with a speaker from the SPK+ and SPK- pins, you’ll definitely need an amplifier such as LM386 (or a crystal earpiece), before you’ll be able to hear anything.
I have not yet had the time to try the serial mode for playback on this module yet. Or perhaps my time should be better spent on figuring out how to get a free sample of the ‘real’ STA013 MP3 player IC from STMicroelectronics and get it to work. All of my attempts to submit a free samples order, however, have been rejected.