AVR recycling

Initially I wanted to use a PDIP ATmega168, but it was just way too large. The knock sensor needs some more space, as it needs an opamp. Luckily the latest LED Ring boards already include a 5V regulator, which saves some more space. The number of available IO pins is sufficient as well (6 including RX/TX, but only RX is shared).

I added a jumper to disconnect the reed relay from the RX pin when I need to update the code. It turns out that a load of 500Ω doesn't interfere at all. I can hear the relay click happily during upload.