MEGA 1280 and 3.3V sensors

[UndCon]

HI!

As I have a MEGA1280 lying unused I figured I could connect my sensors to this board as well...

I have ADXL345, BMP085 along with the WM? and NK

On Jussi's boards (and similar) there is a 3.3V output and in some schematics there are a LLC (low level converter) in use

Do We need to use a LLC when the MEGA1280 has 3.3V out?

The SDA/SCL are not affected right?

I also have 2 LLC's available and figured I could connect everything on a MEGA prototype board

//UndCon

[noobee]

if the processor is powered by 5v, then i think you need the llc for the scl/sda lines to convert between the 5v processor and 3.3v devices.

[quax]

The ATmega has defined 3.0V as a garanteed value for a high level detection with Vcc=5V. If you deactivate the internal pullups of the ATmega and put 2k7 resistors to 3V3 as pullups on SDA and SCK, then you can be sure, that the components will communicate without problems. I tested it with about 2k5 and had a very good connection with a 400kHz I2C-clock.