Question

how to solve the bouncing issues when using the HCSR04 sensor

Answer 1

To start the distance measurement the TRIGGER pin of HC-SR04 must receive a pulse of high (5V) for at least 10us, this will initiate the sensor will transmit out 8 cycle of ultrasonic burst at 40kHz and wait for the reflected ultrasonic burst. When the sensor detected ultrasonic from receiver, it will set the Echo pin to high (5V) and delay for a period (width) which proportion to distance. To obtain the distance, measure the width (Ton) of Echo pin.

Time = Width of Echo pulse, in uS (micro second)

• Distance in centimeters = Time / 58
• Distance in inches = Time / 148

To generate the right TRIGGER signal and measure the ECHO impulse it is required a program that runs in Linux Kernel space and send back to the user space the measurement done.

Code is

	#include <linux/version.h>
	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/gpio.h>
	#include <linux/delay.h>
	#include <linux/kernel.h>
	#include <linux/moduleparam.h>
	#include <linux/init.h>
	#include <linux/hrtimer.h>
	#include <linux/ktime.h>
	#include <linux/device.h>
	#include <linux/kdev_t.h>
	#include <linux/interrupt.h>
	MODULE_LICENSE("Dual BSD/GPL");
	MODULE_AUTHOR("Sergio Tanzilli");
	MODULE_DESCRIPTION("Driver for HC-SR04 ultrasonic sensor");
	// Change these two lines to use differents GPIOs
	#define HCSR04_ECHO 95 // J4.32 - PC31
	#define HCSR04_TRIGGER 91 // J4.30 - PC27
	//#define HCSR04_TEST 5 // J4.28 - PA5
	// adaptation for kernels >= 4.1.0
	#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,1,0)
	#define IRQF_DISABLED 0
	#endif
	static int gpio_irq=-1;
	static int valid_value = 0;
	static ktime_t echo_start;
	static ktime_t echo_end;
	// This function is called when you write something on /sys/class/hcsr04/value
	static ssize_t hcsr04_value_write(struct class *class, struct class_attribute *attr, const char *buf, size_t len) {
	printk(KERN_INFO "Buffer len %d bytes\n", len);
	return len;
	}
	// This function is called when you read /sys/class/hcsr04/value
	static ssize_t hcsr04_value_read(struct class *class, struct class_attribute *attr, char *buf) {
	int counter;
	// Send a 10uS impulse to the TRIGGER line
	gpio_set_value(HCSR04_TRIGGER,1);
	udelay(10);
	gpio_set_value(HCSR04_TRIGGER,0);
	valid_value=0;
	counter=0;
	while (valid_value==0) {
	// Out of range
	if (++counter>23200) {
	return sprintf(buf, "%d\n", -1);;
	}
	udelay(1);
	}
	//printk(KERN_INFO "Sub: %lld\n", ktime_to_us(ktime_sub(echo_end,echo_start)));
	return sprintf(buf, "%lld\n", ktime_to_us(ktime_sub(echo_end,echo_start)));;
	}
	// Sysfs definitions for hcsr04 class
	static struct class_attribute hcsr04_class_attrs[] = {
	__ATTR(value, S_IRUGO | S_IWUSR, hcsr04_value_read, hcsr04_value_write),
	__ATTR_NULL,
	};
	// Name of directory created in /sys/class
	static struct class hcsr04_class = {
	.name = "hcsr04",
	.owner = THIS_MODULE,
	.class_attrs = hcsr04_class_attrs,
	};
	// Interrupt handler on ECHO signal
	static irqreturn_t gpio_isr(int irq, void *data)
	{
	ktime_t ktime_dummy;
	//gpio_set_value(HCSR04_TEST,1);
	if (valid_value==0) {
	ktime_dummy=ktime_get();
	if (gpio_get_value(HCSR04_ECHO)==1) {
	echo_start=ktime_dummy;
	} else {
	echo_end=ktime_dummy;
	valid_value=1;
	}
	}
	//gpio_set_value(HCSR04_TEST,0);
	return IRQ_HANDLED;
	}
	static int hcsr04_init(void)
	{
	int rtc;
	printk(KERN_INFO "HC-SR04 driver v0.32 initializing.\n");
	if (class_register(&hcsr04_class)<0) goto fail;
	//rtc=gpio_request(HCSR04_TEST,"TEST");
	//if (rtc!=0) {
	// printk(KERN_INFO "Error %d\n",__LINE__);
	// goto fail;
	//}
	//rtc=gpio_direction_output(HCSR04_TEST,0);
	//if (rtc!=0) {
	// printk(KERN_INFO "Error %d\n",__LINE__);
	// goto fail;
	//}
	rtc=gpio_request(HCSR04_TRIGGER,"TRIGGER");
	if (rtc!=0) {
	printk(KERN_INFO "Error %d\n",__LINE__);
	goto fail;
	}
	rtc=gpio_request(HCSR04_ECHO,"ECHO");
	if (rtc!=0) {
	printk(KERN_INFO "Error %d\n",__LINE__);
	goto fail;
	}
	rtc=gpio_direction_output(HCSR04_TRIGGER,0);
	if (rtc!=0) {
	printk(KERN_INFO "Error %d\n",__LINE__);
	goto fail;
	}
	rtc=gpio_direction_input(HCSR04_ECHO);
	if (rtc!=0) {
	printk(KERN_INFO "Error %d\n",__LINE__);
	goto fail;
	}
	// http://lwn.net/Articles/532714/
	rtc=gpio_to_irq(HCSR04_ECHO);
	if (rtc<0) {
	printk(KERN_INFO "Error %d\n",__LINE__);
	goto fail;
	} else {
	gpio_irq=rtc;
	}
	rtc = request_irq(gpio_irq, gpio_isr, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING | IRQF_DISABLED , "hc-sr04.trigger", NULL);
	if(rtc) {
	printk(KERN_ERR "Unable to request IRQ: %d\n", rtc);
	goto fail;
	}
	return 0;
	fail:
	return -1;
	}
	static void hcsr04_exit(void)
	{
	if (gpio_irq!=-1) {
	free_irq(gpio_irq, NULL);
	}
	gpio_free(HCSR04_TRIGGER);
	gpio_free(HCSR04_ECHO);
	class_unregister(&hcsr04_class);
	printk(KERN_INFO "HC-SR04 disabled.\n");
	}
	module_init(hcsr04_init);
	module_exit(hcsr04_exit); It generate a TRIGGER pulse when any program tries to read the contents of this file then use an interrupt routine and an hi-res timer to measure the incoming pulse on the ECHO line.

Note: Please connect the GND pin first before supplying power to VCC. Please make sure the surface of object to be detect should have at least 0.5 meter2 for better performance.