I just posted the following warning to the www.w0eb.com website and want to make sure everyone that has constructed or is constructing one of our BITeensio boards gets the following critical information.
It has recently come to my attention that the tiny power jumper on the back of the Teensy 3.5 or 3.6 MUST be cut when using external power to the Teensy (from the BITeensio board). Left intact, it is possible to have power being applied to the Teensy through BOTH the BITeensio board AND the USB connection, especially during programming or remote control operation via the USB port. This causes board power and USB power to conflict with each other and can destroy the Teensy. The jumper is pointed out on the back side of the pin-out card that comes with every Teensy and it states: "Cut to separate VIN from VUSB, if using a battery charger or external power." with an arrow pointing to the jumper between the two pads.
Carefully cut this tiny jumper with a very sharp hobby knife to avoid any possible problems. After cutting the jumper, you will have to power the board externally through the BITeensio card (or other means) when programming or re-programming the Teensy through the USB port. This holds true for Teensy boards used in just about any application, not just on our BITeensio board.
Jim Sheldon, W0EB