CPython or MicroPython support for PWM distance sensors

Support Sensors
1

Hi, I’m considering replacing the current pair of analog Sharp Analog Distance Sensors (#2474) I’m using as they’ve been discontinued.

I was wondering if anyone had found any CPython support code or library for converting the output from the Distance Sensors with Pulse Width Output (e.g., #4064, #4071 and #4079) into a numeric value. I understand that an MCU may be more suitable than a Raspberry Pi but I’d rather prefer the latter if possible since that’s what is running my robot OS.

Thanks!

2

Hello.

Unfortunately, I do not have a CPython example program that will run on a Raspberry Pi computer, but here is a MicroPython example (which we know works on a Raspberry Pi Pico) written earlier this year by one of our summer interns:

# Example MicroPython program for reading the
# Pololu Distance Sensors with Pulse Width Output
import time
import machine
from machine import Pin

# Change the '17' to the digital pin number connected to the sensor's OUT pin.
sensorPin = Pin(17, Pin.IN)

while True:
    # Measure the pulse width.
    t = machine.time_pulse_us(sensorPin, 1)

    if t == 0:
        # time_pulse_us() did not detect the start of a pulse within 1 second.
        print("timeout")

    elif t > 1850:
        # No detection.
        print("Out of range")

    else:
        # Valid pulse width reading. Converts pulse width in microseconds to 
        # distance in millimeters.
        # Uncomment the appropriate line for your sensor.
        d = (t - 1000) * 3 / 4 #4064 - 50 cm max sensor
        #d = (t - 1000) * 2     #4071 - 130 cm max sensor
        #d = (t - 1000) * 4     #4079 - 300 cm max sensor

        # Limit minimum distance to zero.
        if d < 0:
            d = 0

        print(str(d) + " mm")

If you make a CPython example, please consider posting it here since that might be a useful resource for others.

- Patrick

3

Thanks very much! I don’t have the hardware in stock but am considering an order, so if I do end up with one to try I’ll certainly post any code I create here.

I think the tricky part in CPython (that’s clearly simple in MicroPython) would be that first line:

t = machine.time_pulse_us(sensorPin, 1)

But I’ve written a handler for motor encoders in CPython so it’s not exactly rocket science. Thanks for the basic algorithm, it’s a good guide.

1 Like