Switch between Bluetooth and USB-UART bridge works partially

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Joined Aug 30, 2013
I designed this project to control an Arduino (custom board, 5V, 16MHz) wirelessly and its supposed to also work with the USB-UART bridge. I made this work through a multiplexer. When the USB cable gets plugged in, it isolates the BT module and cuts off power to it enabling comms only through the USB port. When the cable is unplugged, the BT module becomes active.

This works partially. This has the grbl firmware for stepper motion control programmed and I can communicate with grbl using the serial monitor, through both BT and the USB-UART. However, I cannot program the Arduino with this setup. I'm stumped as to why this won't work and any ideas would be really helpful.

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