I have a current sensor that sends and receives using I2C, and I have a serial LCD that can use uart(rs232), SPI, and I2C. Are there enough pins for two I2C devices or should i use UART for the LCD, or do i need a more advanced arduino?
Current sensor: http://www.parallax.com/product/29130
LCD: http://www.newhavendisplay.com/specs/NHD-0420D3Z-NSW-BBW-V3.pdf
One of the big advantages of using I2C is that you can wire many I2C devices (up to 127 in theory) to the same two arduino I2C pins. It's a 'shared' bus where every device on the I2C bus has it's own unique 7 bit address so the wiring library handles passing the data to and from the proper device attached.
You should be able to have the LCD and sensors share the I2C bus, the LCD is at address 0x50 (user changeable anyway) and the sensor at any one of 16 possible addresses. That said you could also use SPI fo rit and I2C fo rthe sensor. Either way will should work.
BTW, despite what they say in the docs that LCD does NOT use RS-232, it uses async serial at "TTL" levels, but most people (even these presumed professionals) mistake that for RS-232.
Rob