Level Shifting with Data Logger and Multiple Sensors

Hey guys,

So I am going to be using a Mega 2560 and and a data logger shield (this one in specific Adafruit Assembled Data Logging shield for Arduino : ID 1141 : $13.95 : Adafruit Industries, Unique & fun DIY electronics and kits) and am going to be hooking up one 5V sensor, and two 3.3V sensors to the same I2C bus. My question is, because this has a level shifter in it for the SD card, can I just hook up the sensors to the appropriate power rails, and then tie in the SDA and SCL pins from each sensor together to get accurate sensor readings from each sensor? If you look at page three of the sensor, you will see the power rails. So for the 2 power pins of the sensors, I was going to run them to the appropriate rails, and then in the middle where the protoyping section is, I was going to solder together 4 pins for the SCL and 4 pins for the SDA. I was going to run the 3 SDA lines from the sensors to those lines, and have the last line going to appropriate SDA pin (pin 20 on the MEGA 2560) and then have the other 3 SCL pins run to the SCL header, and the last pin running to pin 21 of the MEGA 2560 for the SCL line. Is this okay? It seemed like when I say level shifters that you have to hook up the SCL and SDA lines and run them a level shifter too but I am not too positive about it in regards to this. I looked through the datasheet and it is not very clear. Sorry, I am kind of a noob at all of this. Thanks.

You lost me after the second sentence. Break up the massive paragraph, please.

You need a separate, I2C capable (bidirectional) level shifter for the 3.3V sensors. The SD card uses the SPI bus has no connection to the I2C bus.

So the level shifter is for the SPI interface and has nothing to do with the I2C bus. So if I want the I2C sensors to function properly with each other appropriately then I can pass the 5V sensor through a I2C bi directional level shifter to get it down to 3.3V which will allow it to work alongside the other 3.3V sensors.

Perhaps incorrect, not sure exactly how you see the configuration.

I2C is a two wire parallel bus. The 5 volt sensors connect directly to the SDA/SCL lines of the Arduino. Also connected to the same SDA/SCL lines is the 5 volt side of the level shifter. The 3.3 volt sensors connect to the low voltage side of the level shifter.

Be aware that different Arduino boards have very different 3.3 volt supply capabilities.