The NVIDIA Jetson Nano is a great device and its choice of I/O is ideal for user space development. If you are a kernel hacker, however, you will soon feel the need for serial console and a reset button. If you want to hack the bootloader you will also need a recovery button. The Nanobug integrates a UART to USB and buttons into a little board that plugs directly into the nano developer kit. To aid automated testing it is possible to control the buttons through USB as well.
The circuit is quite simple. It uses the common FTDI FT230X for the USB to UART functionality. The 4 GPIOs available on the FT230X are used to control the Power, Reset and Recovery signals and the last remaining pin is used for UART Rx/Tx. The USB portion is straight from the FT230X datasheet. Q1-Q3 isolate the FT230X from the buttons so the system will work properly even when the USB is not plugged in. R7 should be assembled to disable the auto power on feature of the Nano developer kit.
If the USB to UART is not needed, the board may be assembled with just the buttons, the J2 and J3 connectors and optionally R7 to only add the button functionality.