I have an I2CXL sonar sensor that I want to use for altitude measurements indoors. I've connected it to the I2C extender that came with the Pixhawk but for some reason the Pixhawk doesn't seem to see it. The PX4 site isn't very helpful, just saying that up to 6 are supported on the I2C bus. I read elsewhere that I need to make driver for it, but the PX4 site doesn't mention this. If anyone else has had this problem, please let me know what I need to do to fix it.