So I have a 3.3 vDC SamD21G18 board running on 3.3 volts DC and the only 2 wires hooked up we’re the ground and the TX pin how could I brick 2 different devices one that 5 vDC tolerant… anyone have some answers ?
Not sure how, but on the Xenon there are no 5V tolerant GPIOs.
How long are your wires?
Got a schematic diagram?
Not much to diagram … Gnd 6” jumper … TX 6” jumper
And my device is 3.3 power and regulate work or it would have bricked that as well if there were issues
Not sure how this then fits into the picture 
Yes Very Odd…Would a bad Ground cause a feed back into the Particle burning out the Voltage regulator ?
If the voltage on the GND pin would be higher than the level on the RX pin or the voltage difference between RX and GND exceeds 3.6V then chances are that the device takes a hit.
Longish wires can act like antennae and may pick up induced voltage from EMI.