AML-S905X-CC with HC-SR04

General
1

I’m working to hook up three HC-SR04 proximity sensors to my Le Potato via GPIO pins.

I’m following this guide for reading the pin states.

I need to figure out how to measure (as accurately as possible) how long the echo pin goes high for, as this is how to determine distance.

Starting this thread to document what I figure out. Also, any advice is appreciated too.

2

I’ve found this video to be invaluable: https://youtu.be/C02oB1n7rcg?si=rWHxMEmTrQjBU3Us

I figured out my model of the HC-SR04 (there are many) outputs 5v on the echo pin, so I created a voltage divider like such for all three to bring the voltage down to about 3.4v.

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3

That video made by Lori Pfahler helped out so immensely.

Here is a short demonstration script for how to get the distances for all three sensors using AML-S905X-CC with HC-SR04 (5v echo output).

from datetime import datetime
from time import sleep
from gpiod import Chip, LINE_REQ_DIR_OUT, LINE_REQ_DIR_IN

forward_ultrasonic_sensor = {
    "trigger": {"chip":"1","offset":91},
    "echo": {"chip":"1","offset":95}
}

left_ultrasonic_sensor = {
    "trigger": {"chip":"1","offset":92},
    "echo": {"chip":"1","offset":81}
}

right_ultrasonic_sensor = {
    "trigger": {"chip":"0","offset":6},
    "echo": {"chip":"1","offset":82}
}

def get_distance(sensor):
    trigger_chip = Chip(sensor["trigger"]["chip"])
    trigger_lines = trigger_chip.get_lines([sensor["trigger"]["offset"]])
    trigger_lines.request(consumer="",type=LINE_REQ_DIR_OUT)

    echo_chip = Chip(sensor["echo"]["chip"])
    echo_lines = echo_chip.get_lines([sensor["echo"]["offset"]])
    echo_lines.request(consumer="", type=LINE_REQ_DIR_IN)

    # Pull pin down to zero volts.
    trigger_lines.set_values([0])
    sleep(0.000002)

    # Set pin high for just 10 microseconds to initiate the trigger
    trigger_lines.set_values([1])
    sleep(0.00001)
    trigger_lines.set_values([0])

    while echo_lines.get_values()[0] == 0:
        continue

    start_time = datetime.now()
    while echo_lines.get_values()[0] == 1:
        continue

    end_time = datetime.now()
    duration_in_seconds = (end_time - start_time).total_seconds()

    distance_in_cm = (duration_in_seconds * 34444) / 2

    return distance_in_cm

forward_distance = get_distance(forward_ultrasonic_sensor)
left_distance = get_distance(left_ultrasonic_sensor)
right_distance = get_distance(right_ultrasonic_sensor)

print(str(forward_distance))
print(str(left_distance))
print(str(right_distance))

Example output below. The left sensor has the most distance shown since that part of my desk is clear and there’s a good distance until the wall. the other two sensors are pretty crowded with toolboxes and such all around.

python3 distance_measurement_demo.py 
14.070374000000001
68.147454
14.345926

The code provided above can be written better. For example you could trigger all three sensors at once via the gpiod library, and you could get all three values from all three sensors at once by getting the lines for all three at once via the gpiod library. Though the intent here is to give a basic example, not final code.

Here is the basic circuit which includes the sensors and the voltage dividers. Note: You do not need the voltage dividers if your sensor echo pin outputs 3.3v. Mine output 5v so I included the voltage dividers to bring voltage down to 3.4v

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As mentioned in the guide, you’d use this command to get the chip and line for each pin number.

lgpio info PIN

So for example to get pin 8, you’d use this command. I put the output just below the command, it shows the chip and line.

lgpio info 8
Chip	Line	sysfs	Name	Pad	Ref	Desc
1	91	492	GPIOX_12	A6	UART_A_TX	UART_TX_A
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