10K series-R with 100 pF to gnd looks like the winner, if wanting to make a reasonable
low-pass filter on RX0.
For reference, you might try the 220K series-R without the 100 pF to gnd, and no pullup.
The first and second waveforms here are useless. The first is basically like smoothing out
a PWM signal to produce a d.c. level, and in the 2nd, the output is too tiny.