lms-esp32-pybricks-info

Using a VL53L0X laser distance sensor with the LMS-ESP32 board from Antons Mindstorms and LEGO® Spike running Pybricks

If you only want to connect a single VL53L0X and expose it as a LEGO compatible sensor, follow Antons article.

If you want to connect multiple sensors and expose them with PUPRemote framework, start with below example that compares LEGO ultrasonic distance sensor with VL53L0X laser distance aka. time of flight sensor.

As already mentioned in Antons article, the VL35L0X by default needs ~30msec for a measurement.

To achieve highest sensor measurement rate, use a separate read thread. The Pybricks rh.call('tof') reads the latest value each ~13 msec.

If using vl53l0x.read() in tof() function instead of using a thread, the Pybricks side would have to use rh.call('tof', wait_ms=30) which would result in a roundtrip time over 40 msec.

LMS-ESP32 code:

from machine import SoftI2C, Pin
from pupremote import PUPRemoteSensor
from VL53L0X import VL53L0X # https://github.com/antonvh/PUPRemote/blob/main/examples/emulate_dist_sensor/VL53L0X.py
import _thread

class VL53L0XThread:
    def __init__(self, device: VL53L0X):
        self.device = device
        self.value = 0
        self.enabled = False

    def _run(self):
        self.device.start()
        while self.enabled:
            self.value = self.device.read()
        self.device.stop()
        self.value = 0

    def start(self):
        self.enabled = True
        _thread.start_new_thread(self._run, ())

    def stop(self):
        self.enabled = False

    def get(self):
        return self.value

vl53l0x = VL53L0X(SoftI2C(scl=Pin(4), sda=Pin(5), freq=200000))
vl53l0xThread = VL53L0XThread(vl53l0x)

def tof(): 
    return vl53l0xThread.get()

def tofOn(on):
    if on:
        vl53l0xThread.start()
    else:
        vl53l0xThread.stop()
  
rs = PUPRemoteSensor(power=True)
rs.add_command('tof', 'H', '')
rs.add_command('tofOn', '', 'B')

while True:
    rs.process()

Add a file named VL53L0X.py with content from https://github.com/antonvh/PUPRemote/blob/main/examples/emulate_dist_sensor/VL53L0X.py

Pybricks code:

from pybricks.pupdevices import UltrasonicSensor
from pybricks.parameters import Port
from pybricks.tools import StopWatch
from pupremote_hub import PUPRemoteHub # https://github.com/antonvh/PUPRemote/blob/main/src/pupremote_hub.py

sw = StopWatch()
us = UltrasonicSensor(Port.B)
rh = PUPRemoteHub(Port.A)
rh.add_command('tof', 'H', '')
rh.add_command('tofOn', '', 'B')

print('time; lego; tof')
rh.call('tofOn', 1)
while True:
    a = us.distance()
    b = rh.call('tof')
    print(f'{sw.time()}; {a}; {b}')

Comparison

Values look comparable and there is nearly no lagging of vl53l0x data that is processed by the LMS-ESP32 first.

Misc

The VL53L0X i used, behaved a bit strange.

• It reported values ~15mm larger than real distance.
• The values for set_measurement_timing_budget are not as documented. With values below ~108 000 it returned False. I had to use:

  value	timing
  0	30 msec
  300 000	20 msec
  200 000	50 msec

I will check again with another device.