0

I am using C/C++ on a rapsberry pi Pico and this is the code I wrote for the sensor:

#include <FreeRTOS.h>
#include <task.h>
#include <stdio.h>
#include <queue.h>
#include <memory>
#include "pico/stdlib.h"
#include "pico/binary_info.h"
#include "one_wire.h"
#include "LCD_I2C.hpp"
#include "i2c-display-lib.h"
#include "hardware/gpio.h"
#include "hardware/timer.h"


void setupUltrasonicPins(uint trigPin, uint echoPin)
{
    gpio_init(trigPin);
    gpio_init(echoPin);
    
    gpio_set_dir(trigPin, GPIO_OUT);
    gpio_set_dir(echoPin, GPIO_IN);

    gpio_pull_up(echoPin);
}



int getPulse(uint trigPin, uint echoPin)
{
    int loop1 = 0;
    int loop2 = 0;
    
    sleep_us(2);
    gpio_put(trigPin, 1);
    sleep_us(20);
    gpio_put(trigPin, 0);
    sleep_us(2);
    
    while (gpio_get(echoPin) == 0)
    {
        loop1++;
        sleep_us(1);
        if(loop1 > 5000){
            printf("\n I got here 1");
            break;
        }
    }

    while (gpio_get(echoPin) != 0 ) 
    {
        loop2++;
        sleep_us(1);
        if(loop2 > 3000){
            printf("I got here 2");
            return 0;
        }
    }
   
    return loop2;
    
}

float getCm(uint trigPin, uint echoPin)
{
    int pulseLength = getPulse(trigPin, echoPin);
    return (float)pulseLength/2  * 0.0343;
}



int main() {
    stdio_init_all();

    //sleep_ms(10000);
    
    uint trigPin = 17;
    uint echoPin = 16;
    setupUltrasonicPins(trigPin, echoPin);

    while(1){
        printf("\n %.2f cm",getCm(trigPin, echoPin));
        sleep_ms(100);

    }
}

Please ignore the extra libraries.

With this sensor you basically have to check how much time has passed between the trigger being activated and the echo receiving a signal so that you can calculate the distance.

The code somewhat works BUT it will show a value for the distance that is always about 30% smaller than the actual distance and from time to time it will fail to provide a value and in the first while it will just timeout and print the message "I got here 1". Sometimes it will also just print a small value like 0.02 for no reason.

Here is the sample of what the result looks like:

 31.59 cm
 31.73 cm
 31.59 cm
 0.02 cm
 31.59 cm
 31.59 cm
 31.73 cm
 32.02 cm
 31.59 cm
 31.61 cm
 31.86 cm
 31.61 cm
 31.73 cm
 31.66 cm
 31.86 cm
 31.88 cm
 31.88 cm
 31.88 cm
 32.00 cm
 I got here 1
 0.00 cm
 I got here 1
 0.00 cm
 31.88 cm
 31.61 cm
 31.61 cm
 31.88 cm
 31.92 cm
 I got here 1
 0.00 cm
 31.88 cm
 31.88 cm
 32.00 cm
 0.02 cm
 0.02 cm
 31.59 cm
 31.59 cm
 31.88 cm
 32.16 cm
 0.02 cm
 0.00 cm
 32.43 cm
 32.16 cm
 32.43 cm
 I got here 1
 0.00 cm
 I got here 1
 0.00 cm

This is what my setup looks like. Just ignore the buzzer in the pic and consider that I used other pins for the trigger and echo.

Schema of the Pico and sensor

Can somebody please help me understand this?

Jonas
  • 121,568
  • 97
  • 310
  • 388
Vlad Dobritoiu
  • 1
  • 1
  • I'm confused. You tagged C++, but I don't see any C++ specific code. You are also using a non-existant language C/C++. The C++ and C languages are different. For example, C++ language allows overloading of functions and operators and C doesn't. This overloading may cause the compiler and linker to use name mangling to resolve symbols. The C language doesn't have this issue. – Thomas Matthews Aug 05 '22 at 22:36
  • Yes, there is only C in the code that I showed here and that I have been using to test the sensor. But I am going to use C++ libraries and C++ for other parts of the same project. I also tagged C++ in this post because the file I used to compile the code is C++ file. I thought that might be relevant. Sorry for the confusion. – Vlad Dobritoiu Aug 05 '22 at 22:41
  • See: https://lastminuteengineers.com/arduino-sr04-ultrasonic-sensor-tutorial/ Then, look at the NewPing library. In particular: https://bitbucket.org/teckel12/arduino-new-ping/src/master/src/NewPing.cpp I think your code handles startup and timeouts differently – Craig Estey Aug 06 '22 at 17:04

0 Answers0