Strange I2C Behavior BMP085


So I am working on building an altimeter for my quadcopter based around the BMP085. I was having a heck of a time getting it to work so I ran the I2C scanner. The BMP085 did NOT show up. To make sure the error was not in the arduino, I hooked up an extra GY-521 board (MPU-6050) I had laying around and it showed up on the scanner, and even weirder was the BMP085 showed up. I ran the altimeter code and it worked, but only when I had the GY-521 also hooked up, even though Im not reading any data from it it makes the other sensor work. Soooo how do i get the 085 to work with out adding an extraneous I2C device? What is going on here?


Hi N314

When using just the BMP085, do you have pullup resistors from SDA and SCL to +5V? If not, maybe the GY-521 breakout board does have these resistors.




Added 4.7k pullups and all is well.

Thanks, -Nick