AWOL:
m12lrpv:
From the datasheet the atmega328 will only reliably register a low on the a digital pin when the voltage is below 0.3v in a 5v system. It has to be above 0.6V to register as high.Wrong on both counts.
Read it again.
Table
ok 0.3 x Vcc so a little bit higher. Op still should do what I advised and log the serial to see what the signal looks like then proceed from there.