I2C communication between sensor and Pysense not working

[ambropete]

Hello all together,

I posted my issue under another topic three weeks ago but it could not be solved and I still got no idea why my setup fails to work. I have a hc-sr04 ultrasonic sensor (5V signal level) level shifted from 5v to 3v3 and connected to the Pysense external I/O header. Echo goes to PIN7, Trigger to Pin8 and Ground to Pin 1. Very sporadically I receive a distance measurement that sometimes seems to be correct and sometimes is 0; 99% of the time, the serial port seems to be dead! Do you have an idea what could be the issue? Is there a mistake in the code? I have two Pysense and the problem with them both. Thank you very much for your time in advance!

import pycom
import time
from machine import Pin, Timer
from machine import I2C
import ubinascii
import micropython


echo = Pin(Pin.exp_board.G17, mode=Pin.IN)
trigger = Pin(Pin.exp_board.G22, mode=Pin.OUT)
trigger(0)
chrono = Timer.Chrono()
while True:
    chrono.reset()

    trigger(1)
    time.sleep_us(10)
    trigger(0)

    while echo() == 0:
        pass

    chrono.start()

    while echo() == 1:
        pass

    chrono.stop()

    distance = chrono.read_us() / 58.0

    if distance > 400:
        print("Out of range")
    else:
        print("Distance {:.0f} cm".format(distance))

    time.sleep(500)