As one who is just starting out to explore the Particle IoT world, I want to be sure I don’t mess up the Photon.
My Photon will be powered from a ‘12V’ battery via the Relay Shield. I would prefer to use a Windows7 PC to do the programming via USB, but am concerned that when I’m doing that I’d be supplying power from two ends, both from the USB and from the Relay Shield.
@brettn, there is a protection diode on the Photon between Vusb and Vin. The Vin pin is used to supply the power to the Photon from the 12v to 5v converter on the shield. This diode will provide the protection you need.