Having got everything pulled back together and wired back up, I can now report that it doesn’t work. Since I don’t own an oscilloscope (yet!) debugging it is going to prove difficult. However, I can’t see anything obvious wrong with my little circuit, so I now rather suspect that I may have blown the UART in the router.
Ideally I should now test that, but again, without an oscilloscope to hand, that’s going to be awkward. If anyone reading this is an electonics wiz, feel free to comment on any issues I may have overlooked in the design of my circuit.
In the meantime I’m going to see about acquiring some test tools to help me debug it further. Drat.