I have a spare BT HomeHub 5a clone (actually a PlusNet Hub One router). I would like to install the OpenWRT firmware on it, in order to reliably use it as a wired wifi range extender without a DHCP server or ADSL connection.
How do I use a Raspberry Pi to connect to the serial connections on the HomeHub, and to perform the firmware upgrade over tftp, so I don't have to affect any other computers in my household?
I did this 6 months ago and it took me ages to collect together all the information I needed in order to use my Raspberry Pi to achieve this.
I needed to do this again and found I could not remember everything, so had to go through the process of finding it all out again.
I am therefore simultaneously asking and answering this question in order to put all the steps in one place for when I need to do this again, and in the hope it may be helpful for others.