I have a Deo Nano SoC piggy backed (via 40pins through 2 dip rows) to my pcb. My pcb has an aux connector that uses an RJ45 connector. The aux pin-out to the color wires is as follows: Green to gnd, Green/W to 3.3v, Orange to a gpio, Orange/W to gnd, Blue to a gpio, Blue/W to gnd, Brown to gpio, Brown/W to gnd.

I have a second pcb attached to the first via the brown wire pair ( ~ 20 inch cable) with a mosfet that drives 4 LEDs and is set up for low duty cycle. The brown pair is soldered to the mosfet pcb and is used to drive the base. The remaining 6 wires are protected with heat shrink (the ends are floating). The GPIOs of the orange and blue are set to high impedance "Z" from the FPGA. The mosfet pcb has a small camera mount is uses as a light ring. The base pin has a 100 ohm series resistor and a 25k pull down resistor at the base. I plug my mosfet board to a 5v power supply board with no problem using a molex type connector. I can flash the LEDs at will using the brown wire as control.

The problem I have is when I connect/disconnect the RJ45 connector, the LEDs flash once longer than the duty cycle I am operating. This is a problem in that I plan to operate the LEDs at higher voltage to provide sufficient light. The long duration from connect/disconnect could cause LED failure. The speed I connect/disconnect the RJ45 connector is proportional to the unwanted flash duration. Any thoughts to why I may be getting the unwanted flash?

 

I think after writing my plea, the issue may be a floating ground versus a defined ground getting pulled together at the RJ45 connection.