Configuration: PocketBeagle (PB) with an I2C connection to a MPU6050 breakout board. Power to the MPU6050 board is 3.3 volts from the PB.
The PB is connected to a CurieNano using uart TX and RX. This is serial port 4. The two boards have their own power supplies. There is a common ground wire between the two boards. This configuration works well and I can send messages between the two boards. The PB has no problem "talking" to the MPU6050. I had the power to the PB disconnected and was just using the CurieNano. I was uploading a script. I noticed that the power LED on the MPU6050 board was on (not very bright). I measured the 3.3 volts line going into the board. It measured 1.7 volts. I also measured the 5 volts output pin on the PB. It measured 1.8 volts. As there was no power to the PB and the only other connection was the serial port, I removed the two wires. The LED went off and the voltages on the PB went to zero. Put the cable back on and voltages come back. I measured the TX and RX line from/to the CurieNano. The TX was 3.0 volts and the RX was 0.08. Removing the I2C cable had no effect. Questions: 1: Had anyone else seen this behavour? How is a voltage on a serial port on a PB with no power showing up (as a lower voltage) on the 5.0 volt and 3.3 volt output pins!! 2: Is this an issue I need to be concerned about. Could it damage the boards? 3: Is this just a design artifact of the OSD3358 when it is powered off the voltage on the RX pin is reflect via some substrate to the voltage output pins? 4: Am I missing something? I have look for any shorts and found none. And anyway the voltage output pads on the IC are nowhere near the serial port 4 pads. Graham -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/9eab48a6-867b-473a-b913-872bc88a4022%40googlegroups.com.
