The i2c bus is active low. Data is transmitted by pulling the data line to ground. When the data line isn't in use it floats to the supply voltage of the bus master.
In this case, everything is OK as you're powering the sensor off the 3v3 Omeaga supply.
If you needed to use a sensor that has (say) a 5v supply, then you have several options.
use a bidirectional opto isolator on tha data line. Only the clock and gnd are connected together.
use a bidirectonal level shifter to conver between the 5v and 3v3 systems , again only the clock and gnd are connected together.
the bus is driven by the master, and its voltage levels. You don't have to do anything special as 5v should never get anywhere near the data lines, and the sensor will pull the data line to gnd when it transmits data (connect the data, clock and gnd together).
Option1is the safest, the Aruinodo dock v2 uses option2 , but I've used option 3 to hook RPIs to Arduinos over i2c, with different supply voltages without anything going bang. The RPi (like the Omega) is a bus master and controls the line levels.
One caveat is if the sensor has pullup resistors to the supply line, so check any circuit diagrams if they are available.
@cas said in Omega2+ losing power / powering off unexpectedly:
The pin pad underneath: <photo>
"Thermal pad is connected to GND layer through vias (recommend 4X4 pins and the aperture is 10mil)." /active-semi/
These holes are (thermal conducting) vias between the top and the bottom copper layers of the PCB.
The bottom of the dock was very hot to the touch, so I suspect I burnt out the ACT2801 which appears to have a pin pad underneath. Actually upon closer inspection of the pin pad, one if the holes appears to be blocked with a silver substance and I can't help wondering if that's solder (if that's at all possible).
Spot the mistake.... ;-)
It's a "perfect" solder material "bead" / "ball" - it's OK here - no problem.
I don't have Power Dock - so I'm speculating based on active-semi's ACT2801 data sheet and Onion's schematics only.
VIN Input Voltage nom. +5V (range +4.5 ... 5.5V), Absolute Max. +6.5V
VIN_OVP Over Voltage Protection typ. +6.0v (range +5.5 ... 6.5V)
So 5.4V was OK.
The IC has an Input Current limiter.
ILIM Input Current Limit - Omega's setting is R2=2.4kΩ about 1A - so the input current couldn't have been more than 1A. (It was 1.8A / 1.9A!)
Please try to recall. You might have done something else or something else might have happened.
Or simply this is one of those cases where Murphy's Law happened to be working.
I had a similar problem, the battery would not charge at all. It worked fine until I drained the battery completely, after that the power dock would no longer charge the battery. Just as a quick experiment I connected the battery to one of my adafruit feather boards and let it charge the battery for 15 minutes, after this it worked fine again and was charged by the power dock.