This is just a reiteration of my post on http://www.eevblog.com/forum/. Since then some people have picked up the challenged and designed new firmware for the microcontroller. Let me explain.
The module is a cheap (2-3$) 0-30V voltmeter. It has a 3-digit output, is pretty accurate and begs curiosity with it's TXD/RXD soldermask labels.
The inside sports an STM800S3F3 chip with nice features:
- 2.95-5.5V supply voltage
- 16 Mhz internal oscillator
- 3 timers
- 4 CCP/PWM modules
- 5-channel 10-bit ADC
- UART, SPI, I2C
- 8k Flash, 1k RAM
SWIM / PD1 (HS)
TX / AIN5(HS) / PD5
RX / AIN6 (HS) / PD6
The board also includes a 3V/30mA linear regulator that can take up to 30V. All-in-all a very cheap development board that can be used for a lot of stuff
Here's a close-up picture of the board under strong light so you can reference the double-sided PCB without taking the thing apart:
And if you want to dig into this deeper just have a look at http://smokedprojects.blogspot.ca/2013/08/i2c-led-display-from-hacked-voltmeter.html and http://hackaday.com/2013/08/25/turning-cheap-voltmeters-into-i2c-displays/.
The board in the article looks slightly different than mine, but I just bought the cheapest one I could find on ebay.