I've been connecting sensors to the i2c line on the apm 2.5 and after a little while the i2c port stops working. This is the second APM this has happened to and I can't keep on spending money.
Here is what I did to trouble shoot. I uploaded the arducopter firmware onto the apm 2.5 and try to connect to mission planner, but it gives me an error that says no packets received. Then I pull up the arduino serial monitor. The first two errors that show up are that the barometer and compass can't be initialized and calibrated respectively.
I just checked the voltage out of the I2C port and it is 228mV, which is really low from the correct 3.3V that the I2C voltage should be at.
I need help soon! This control board is part of my thesis project and the copter needed to be flying yesterday!