CircuitPython and Grove - Ultrasonic Ranger

Products & Technology XIAO
1

I was trying to get the Grove Ultrasonic Ranger to work with CircuitPython on the Xiao, but I believe that it’s simply too slow to handle the timing. I tried looking into this with very simple code:

while True:
    led.value = True
    led.value = False

The resulting pulse hi/low times are 26.4 us, and I don’t see how to get the Ultrasonic Ranger to work with that sort of timing resolution. For reference the trigger pulse is typically 10 us. I even attempted with pulseio, but couldn’t get it to work.

Please let me know if anyone finds a way. Maybe it would need to be a native library written in C?

2

Maybe you can try ArduPy, which has almost the same performance as using C.

3

Any idea if the decorators mentioned in this article could help Embedded Python: Cranking Performance Knob up to Eleven!? Edited to add - these don’t appear to be enabled for this board.

4

Hi Keith, we do have a library for similar device here: https://github.com/adafruit/Adafruit_CircuitPython_HCSR04/blob/master/adafruit_hcsr04.py

What did you try with pulseio? Did you try PulseIn.resume with a trigger duration? https://circuitpython.readthedocs.io/en/latest/autoapi/pulseio/index.html#pulseio.PulseIn.resume That is what we use for DHT11 temp sensors which require a trigger pulse.

5

Ok - I actually had looked at that library and believe that the initial timeout check in the hcsr04 library is what led me astray. It could be added back, but as a quick proof of concept this minimal code does work:

import board
import pulseio
import time

sig = pulseio.PulseIn(board.D7)
sig.pause()
sig.clear()
sig.resume(10)
time.sleep(1) # should poll len(sig) here with a timeout
sig.pause()
print("len(sig) = ", len(sig))
if len(sig) != 0:
    print("sig[0] = ", sig[0])
    print("Distance = {} [cm]".format(sig[0]*0.017))

I’m not sure why that library doesn’t pass a pulse length to resume, and manually toggles the trigger instead?

Anyways I think that this should work as long as pulseio is used.

Without pulseio there are a couple of potential issues. One is speed and being able to toggle pins quickly enough, and make quality measurements. The other issue is time.monotonic() and long run-times. I believe that even with a faster CPU the library would likely fail after a day or so of runtime do to the time being represented by a single precision float. A workaround would be for the higher level application to reset the timebase, but I don’t believe there’s a way to do that.

6

Here’s my attempt at porting the HC-SR04 library:

CircuitPython library for the Grove ultrasonic range sensor

It seems to work o.k. on the Seeeduino Xiao.