HC-SR04超声波传感器的C程序未显示正确的距离

Question

我有一个带有AlphaBot2的Raspberry Pi Zero，它带有HC-SR04超声波传感器。使用Python的实现效果很好。我想用 C 实现，因为我需要将其与另一个程序绑定，也是在 C 中并且出于优化原因。我注意到的第一件事是Python代码使用RPi.GPIO库，在C中我必须使用WiringPi或bcm2835。所以我决定使用布线Pi库。我的程序执行，但距离不正确。与我在web上找到的实现不同的一点是，我使用的是TRIG 22和ECHO 27，因为我的HC-SR04连接到AlphaBot2。我没有使用 2 个电阻器将其连接到树莓派。当我在传感器前面放置一些障碍物时，即使将其移动到 30 厘米，我也只能获得 3 和 5 厘米。

Distance: 3905724cm
Distance: 5cm
Distance: 5cm
Distance: 5cm
Distance: 5cm
Distance: 3cm
Distance: 3cm
Distance: 5cm
Distance: 5cm

这是我的代码：

#include <stdio.h>
#include <stdlib.h>
#include <wiringPi.h>
#include "ultrasonicClient.h"
#define TRUE (1==1)
// HC-SR04 ultrasonic sensor on AlphaBot2 Pi Zero
#define TRIG 22
#define ECHO 27
static volatile long startTimeUsec;
static volatile long endTimeUsec;
double speedOfSoundMetersPerSecond = 340.29;
void recordPulseLength() {
startTimeUsec = micros();
while (digitalRead(ECHO) == HIGH);
endTimeUsec = micros();
}
void setupUltrasonic() {
wiringPiSetup();
pinMode(TRIG, OUTPUT);
pinMode(ECHO, INPUT);
// TRIG pin must start LOW
// Initialize the sensor's trigger pin to low. If we don't pause
// after setting it to low, sometimes the sensor doesn't work right.
digitalWrite(TRIG, LOW);
delay(500); // .5 seconds
}
int getCM() {
// Send trig pulse
// Triggering the sensor for 10 microseconds will cause it to send out
// 8 ultrasonic (40Khz) bursts and listen for the echos.
digitalWrite(TRIG, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG, LOW);
int now = micros();
// Wait for echo start
// The sensor will raise the echo pin high for the length of time that it took
// the ultrasonic bursts to travel round trip.
while (digitalRead(ECHO) == LOW && micros() - now < 30000);
recordPulseLength();
long travelTimeUsec = endTimeUsec - startTimeUsec;
double distanceMeters = 100 * ((travelTimeUsec / 1000000.0) * 340.29) / 2;
//Wait for echo end
long startTime = micros();
while (digitalRead(ECHO) == HIGH);
long travelTime = micros() - startTime;
//Get distance in cm
int distance = travelTime * 34000 / 2;
return distanceMeters * 100;
}
int runUltrasonicClient() {
int count = 0;
setupUltrasonic();
while (count < 60) {
printf("Distance: %dcmn", getCM());
count++;
delay(500); // 0.5 second
}
return 0;
}

Answer 1

我找到了一个使用 bcm2835 执行的代码。

static uint64_t cyclePulse(int trigger, int echo) {
if (!bcm2835_init())
return 1;
// Set RPi pin echo to be an input pin
bcm2835_gpio_fsel(echo, BCM2835_GPIO_FSEL_INPT);
// Set RPi pin P1-11 to be an output pin
bcm2835_gpio_fsel(trigger, BCM2835_GPIO_FSEL_OUTP);
// Declare the unsigned int timer variables to measure pulses
uint64_t width, begin, start, end;
int max = 80, check;
begin = bcm2835_st_read();
// Emit pulse for 10 microseconds
bcm2835_gpio_write(trigger, HIGH); // Set trigger state HIGH
bcm2835_delayMicroseconds(10);  // Wait 10 microseconds
bcm2835_gpio_write(trigger, LOW);  // Set trigger state LOW
// Infinite loop until a pulse is received
while (bcm2835_gpio_lev(echo) == LOW && check < max) {
start = bcm2835_st_read();
check = (int) begin - start;
}
// Loop and delay for one microsecond until falling edge detected
while (bcm2835_gpio_lev(echo) == HIGH) {
bcm2835_delayMicroseconds(1);
}
// Record the ending time of the pulse to get the pulse width
end = bcm2835_st_read();
// Get the final with of the pulse
width = end - start;
//Close the bcm2835 bridge
bcm2835_close();
// Return the total width of the returned pulse
return width;
}