Well, the SMT prototype is almost working. There's some sort of bug (maybe) with the mikroProg programmer I'm using which seems to be ignoring the CPUDIV configuration fuse that I need. As a result the MCU clock runs at 48 MHz instead of 24 MHz...not good. The LCD shows that it is trying to establish a USB connection but not quite making it.
I put an OnSemi MC14066B Quad Bilateral Switch on the prototype (instead of the Maxim MAX4066 that I originally intended). The MAX4066 has a lower "on" resistance (around 45 Ω compared to about 100 Ω for the MC14066B at 5V) but it's probably more important that the "off" resistance is high - otherwise you could see weird behaviour. Still not tested yet, but in theory it should work.
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