Thinking more on this, the alternating 0 with non-0 readings were probably due to having the
trigger pulses so close together that the units hadn't finished the previous "full" cycle before
the next trigger came along. So increasing delay from 10 to 100-msec fixed that.
As far as noise goes, there isn't much noise in the good sets of readings, the only anomaly is
the first EZ4 reading is much lower than the others. I don't know why, but probably should take
more than 1 reading and throw the first away every time. ????
I don't know what spikes you are seeing. I don't have the 100-100 filter you show, but do actually
have a 100-uF cap on the Vdd buss in the area that feeds the sonars.
Also, as noted last time, I think the short readings are largely due to ground clutter pickup.
I have one more test to try.