Written by Anna Zeng, updated by Jennifer Lin
To reboot the Pi without unplugging and replugging in the USB-serial adapter, we can make use of the reset pin on the Pi. In the photo below, look for the red circle around two holes labeled “RUN”. The “RUN” hole is connected to the reset pin on the processor. When this pin is temporarily pulled low, the Raspberry Pi will reset.
This guide walks you through soldering a 2-pin header onto the RUN contacts and running jumpers from the header pins to a button or, better, a software switch controlled by
rpi-install.py via the DTR pin on the USB-serial adapter.
Grab a 2-pin header (available in our lab cabinet) and place onto the RUN contacts as shown below:
Heat the soldering iron to approximately 600 degrees F (60 on the dial), and wait until the light blinks rapidly.
While holding the soldering iron like a pen, touch the solder on one side of the pin and hold the soldering iron on the other side. The iron will heat up the pin and pad and the liquid solder will flow over the joint and forms a little volcano.
Once the joint is complete, remove the soldering iron and the solder. Repeat for the second pin. The contacts will look sort of like this:
If you temporarily connect the two header pins (such as by using a jumper or a pair of metal tweezers), your Pi should restart. This is a good test to verify your solder connections.
Once you have installed the header, if you attach two jumpers that connect the pins through a button, the button will act as hardware reset switch. Simply press the button to reset the Pi. Handy!
To take it to the next level, you can connect the RUN pin on the Pi to the DTR pin on your USB-serial adapter. When the USB-serial pulls the DTR pin to ground, it will trigger your Pi to restart. Find the pin labeled “DTR” on your USB-serial adapter. Use a jumper to connect the DTR pin to the RUN pin on your Pi. (We used a white jumper in the photos below.)
With this connection in place, pulling DTR to ground will now reset the Pi. When sending a program to the bootloader using our
rpi-install.py script, the first thing the script does is pull DTR to ground. This means it will automatically reset the Pi so it is ready to receive the new program. No more USB plugging and unplugging for you – super-cool!
Note to users of the Windows VM: Using your reset header as a hardware switch will work, but the VM does not support software reset via DTR. We are looking into it and will let you know if we come up with a workaround. (January 2019)