DHT11 实现温湿度传感器

DHT11
DHT11是一款含有已校准数字信号输出的温湿度复合传感器，它结合了电阻式感湿元件和一个NTC测温元件，并与一个高性能8位单片机相连接。通过采用专用的数字模块采集技术和温湿度传感技术，DHT11确保了产品的高可靠性和长期稳定性

DHT11时序部分主要为 DHT11启动时序，读取数字0和读取数字1

1 . DHT11启动时序

①

主机首先将电平拉低，至少持续18us [ mdelay(20) ]，随后再拉高；

static void dht11_start(void)
{
	gpio_direction_output(PIN_DHT11, 0);
	mdelay(20);
	gpio_set_value(PIN_DHT11, 1);
	udelay(30);
	gpio_direction_input(PIN_DHT11); 
//将引脚设置为输入模式开始读取数据
}

②

随后读取HDT发送的响应，先是80us的低电平随后拉高至80us；
表明DHT11已经正确响应启动信号，即将开始传输数据

static int dht11_wait_repon(void)
{
	int time = 100;
	while(gpio_get_value(PIN_DHT11))   // wait H end
	{
		udelay(1);
		if(!time--)
			return -1;
	}

	time = 100;
	while(!gpio_get_value(PIN_DHT11) && time)  // wait 80us L end
	{
		udelay(1);
		if(!time--)
			return -2;
	}

	time = 100;
	while(gpio_get_value(PIN_DHT11))   // wait 80us H end
	{
		udelay(1);
		if(!time--)
			return -3;
	}

	return 0;
}

2 . 读取0/1

①
当在启动时序的最后拉高80us后，如果遇到拉低50us和拉高26-28us则表示读取到 ‘ 0 ’；

当在启动时序最后，如果遇到了拉低50us和拉高70us则表示读取到 ‘ 1 ’ ；

所以可以根据高电平拉高时间来判断读取的是 ‘ 0 ’ 或者 ‘ 1 ’；

②
判断数据是都传输正确
数据接收完毕后，根据ret的值进行检验，如果hum_h、hum_l、temp_h、temp_l 相加的值的后8位和校验位不相等，那么此次数据作废。

static int dht11_get_value(unsigned char * data)
{
	int i = 0;
	int j = 0;
	unsigned char sum = 0;
	for(i = 0; i < 5; i++)
	{
		data[i] = 0;
		for(j = 0; j < 8; j++)
		{
			char bit = dht11_get_bit();	
			if(bit < 0)
				return bit;
			data[i] <<= 1;
			data[i] |= bit;
		}
	}

	for(i = 0; i < 4; i++)
	{
		sum += data[i];
	}

	if(sum == data[4])
		return 4;
	else
		return -1;
}

=== 数据格式：

DHT11采用单总线双向串行通信协议，每次采集信号时，都需要单片机向DHT11发送开始信号。DHT11在接收到开始信号后，即发送40bit的数据给单片机。高位在前，数据格式为：

湿度高8位+湿度低8位+温度高8位+温度低8位+8bit校验位

其中8bit校验位的值应与前4个8位数据相加后的数的低8位相同，如果不同则放弃本次数据

实践流程：

①编写dht11.c

②make Makefile 与 make Kconfig

③make modules 生成 dht11,ko

④cp drivers/char/dht11.ko /home/linux/nfs/rootfs

⑤编写dht11_app.c 在 /home/linux/nfs/rootfs下

⑥arm-linux-gcc dht11_app.c -o dht_app

⑦sudo minicom

⑧insmod dht11.ko

⑨./dht11_app

完整代码

dht11.c

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/module.h>
#include <asm/io.h>
#include <asm/string.h>
#include <asm/uaccess.h>
#include <linux/miscdevice.h>
#include <asm-generic/errno-base.h>
#include <mach/gpio-nrs.h>
#include <mach/gpio.h>
#include <linux/delay.h>

#define DEV_NAME "dht11"
#define PIN_DHT11 S3C2410_GPF(6)

static void pin_init(void)
{
	gpio_request(PIN_DHT11, "dht11");
}

static void dht11_start(void)
{
	gpio_direction_output(PIN_DHT11, 0);
	mdelay(20);
	gpio_set_value(PIN_DHT11, 1);
	udelay(30);
	gpio_direction_input(PIN_DHT11);
}

static int dht11_wait_repon(void)
{
	int time = 100;
	while(gpio_get_value(PIN_DHT11))   // wait H end
	{
		udelay(1);
		if(!time--)
			return -1;
	}

	time = 100;
	while(!gpio_get_value(PIN_DHT11) && time)  // wait 80us L end
	{
		udelay(1);
		if(!time--)
			return -2;
	}

	time = 100;
	while(gpio_get_value(PIN_DHT11))   // wait 80us H end
	{
		udelay(1);
		if(!time--)
			return -3;
	}

	return 0;
}

static int dht11_get_bit(void)
{
	int time = 100;
	while(!gpio_get_value(PIN_DHT11))  // wait 50us L end
	{
		udelay(1);	
		if(!time--)
			return -1;
	}

	udelay(30);

	if(0 == gpio_get_value(PIN_DHT11))
		return 0;

	while(gpio_get_value(PIN_DHT11))   // wait 40us H end
	{
		udelay(1);	
		if(!time--)
			return -2;
	}

	return 1;
}

static int dht11_get_value(unsigned char * data)
{
	int i = 0;
	int j = 0;
	unsigned char sum = 0;
	for(i = 0; i < 5; i++)
	{
		data[i] = 0;
		for(j = 0; j < 8; j++)
		{
			char bit = dht11_get_bit();	
			if(bit < 0)
				return bit;
			data[i] <<= 1;
			data[i] |= bit;
		}
	}

	for(i = 0; i < 4; i++)
	{
		sum += data[i];
	}

	if(sum == data[4])
		return 4;
	else
		return -1;
}

static int open (struct inode * inode, struct file * file)
{
	pin_init();
	printk("dht11 open ...\n");
	return 0;
}

static ssize_t read (struct file * file, char __user * buf, size_t len, loff_t * offset)
{
	unsigned char data[4] = {0};
	int ret = 0;
	dht11_start();
	ret = dht11_wait_repon();
	if(ret < 0)
		goto err_wait;

	ret = dht11_get_value(data);
	if(ret < 0)
		goto err;

	copy_to_user(buf, data, sizeof(data));

	printk("dht11 read ...\n");
	return sizeof(data);

err_wait:
	printk("dht11_wait_repon err ... \n");
	return ret;

err:
	printk("dht11_get_value err ...\n");
	return ret;
}

static ssize_t write (struct file * file, const char __user * buf, size_t len, loff_t * offset)
{
	return 0;
}

static int close (struct inode * inode, struct file * file)
{
	printk("dht11 close ...\n");
	return 0;
}

static struct file_operations fops = 
{
	.owner = THIS_MODULE,
	.open = open,
	.read = read,
	.write = write,
	.release = close
};

static struct miscdevice misc = 
{
	.minor = MISC_DYNAMIC_MINOR,
	.name = DEV_NAME,
	.fops = &fops
};

static int __init dht11_init(void)
{
	int ret = misc_register(&misc);
	if(ret < 0)
		goto err_misc_register;

	printk("dht11_init  ...\n");
	return ret;

err_misc_register:
	misc_deregister(&misc);
	printk("dht11 misc_register faidht11\n");	
	return ret;
}

static void __exit dht11_exit(void)
{
	misc_deregister(&misc);
	printk("dht11_exit  ###############################\n");
}

module_init(dht11_init);
module_exit(dht11_exit);
MODULE_LICENSE("GPL");

hdt11_app.c

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/module.h>
#include <asm/io.h>
#include <asm/string.h>
#include <asm/uaccess.h>
#include <linux/miscdevice.h>
#include <asm-generic/errno-base.h>
#include <mach/gpio-nrs.h>
#include <mach/gpio.h>
#include <linux/delay.h>

#define DEV_NAME "dht11"
#define PIN_DHT11 S3C2410_GPF(6)

static void pin_init(void)
{
	gpio_request(PIN_DHT11, "dht11");
}

static void dht11_start(void)
{
	gpio_direction_output(PIN_DHT11, 0);
	mdelay(20);
	gpio_set_value(PIN_DHT11, 1);
	udelay(30);
	gpio_direction_input(PIN_DHT11);
}

static int dht11_wait_repon(void)
{
	int time = 100;
	while(gpio_get_value(PIN_DHT11))   // wait H end
	{
		udelay(1);
		if(!time--)
			return -1;
	}

	time = 100;
	while(!gpio_get_value(PIN_DHT11) && time)  // wait 80us L end
	{
		udelay(1);
		if(!time--)
			return -2;
	}

	time = 100;
	while(gpio_get_value(PIN_DHT11))   // wait 80us H end
	{
		udelay(1);
		if(!time--)
			return -3;
	}

	return 0;
}

static int dht11_get_bit(void)
{
	int time = 100;
	while(!gpio_get_value(PIN_DHT11))  // wait 50us L end
	{
		udelay(1);	
		if(!time--)
			return -1;
	}

	udelay(30);

	if(0 == gpio_get_value(PIN_DHT11))
		return 0;

	while(gpio_get_value(PIN_DHT11))   // wait 40us H end
	{
		udelay(1);	
		if(!time--)
			return -2;
	}

	return 1;
}

static int dht11_get_value(unsigned char * data)
{
	int i = 0;
	int j = 0;
	unsigned char sum = 0;
	for(i = 0; i < 5; i++)
	{
		data[i] = 0;
		for(j = 0; j < 8; j++)
		{
			char bit = dht11_get_bit();	
			if(bit < 0)
				return bit;
			data[i] <<= 1;
			data[i] |= bit;
		}
	}

	for(i = 0; i < 4; i++)
	{
		sum += data[i];
	}

	if(sum == data[4])
		return 4;
	else
		return -1;
}

static int open (struct inode * inode, struct file * file)
{
	pin_init();
	printk("dht11 open ...\n");
	return 0;
}

static ssize_t read (struct file * file, char __user * buf, size_t len, loff_t * offset)
{
	unsigned char data[4] = {0};
	int ret = 0;
	dht11_start();
	ret = dht11_wait_repon();
	if(ret < 0)
		goto err_wait;

	ret = dht11_get_value(data);
	if(ret < 0)
		goto err;

	copy_to_user(buf, data, sizeof(data));

	printk("dht11 read ...\n");
	return sizeof(data);

err_wait:
	printk("dht11_wait_repon err ... \n");
	return ret;

err:
	printk("dht11_get_value err ...\n");
	return ret;
}

static ssize_t write (struct file * file, const char __user * buf, size_t len, loff_t * offset)
{
	return 0;
}

static int close (struct inode * inode, struct file * file)
{
	printk("dht11 close ...\n");
	return 0;
}

static struct file_operations fops = 
{
	.owner = THIS_MODULE,
	.open = open,
	.read = read,
	.write = write,
	.release = close
};

static struct miscdevice misc = 
{
	.minor = MISC_DYNAMIC_MINOR,
	.name = DEV_NAME,
	.fops = &fops
};

static int __init dht11_init(void)
{
	int ret = misc_register(&misc);
	if(ret < 0)
		goto err_misc_register;

	printk("dht11_init  ...\n");
	return ret;

err_misc_register:
	misc_deregister(&misc);
	printk("dht11 misc_register faidht11\n");	
	return ret;
}

static void __exit dht11_exit(void)
{
	misc_deregister(&misc);
	printk("dht11_exit  ###############################\n");
}

module_init(dht11_init);
module_exit(dht11_exit);
MODULE_LICENSE("GPL");