从事IOT行业，难免需要与硬件打交道；
今天正好领导要求，让我使用树莓派通过GPIO从DHT11温湿度传感器上采集温湿度信息，并将温湿度信息存到一个指定的H2DB中；
一、学习本章节的基础
首先，你得懂python，至少得能看懂我的代码，知道如何使用pip安装依赖包；
其次，你得懂树莓派，树莓派其实就是一个简单的Linux系统（ubuntu）；
再然后，你得懂GPIO，知道如何去接线，知道哪些针应该连到哪个触角上；
最后，你还得懂H2DB，这个数据库虽然不难，有点类似于mysql，但毕竟工作中用的少！
二、直接上手开干
1、了解DHT11温湿度传感的线路图：
可以参考本篇文章：https://blog.csdn.net/weixin_54039182/article/details/124854207
2、了解GPIO的引脚对应表：
其中土黄色圈出来的引脚，是我选择使用的引脚！
3、编写python脚本（包含DHT11的读取和数据库写入的逻辑）：
import RPi.GPIO as GPIO
import jaydebeapi
import time
DHTPIN = 17
GPIO.setmode(GPIO.BCM)
MAX_UNCHANGE_COUNT = 100
STATE_INIT_PULL_DOWN = 1
STATE_INIT_PULL_UP = 2
STATE_DATA_FIRST_PULL_DOWN = 3
STATE_DATA_PULL_UP = 4
STATE_DATA_PULL_DOWN = 5
def read_dht11_dat():
GPIO.setup(DHTPIN, GPIO.OUT)
GPIO.output(DHTPIN, GPIO.HIGH)
time.sleep(0.05)
GPIO.output(DHTPIN, GPIO.LOW)
time.sleep(0.02)
GPIO.setup(DHTPIN, GPIO.IN, GPIO.PUD_UP)
unchanged_count = 0
last = -1
data = []
while True:
current = GPIO.input(DHTPIN)
data.append(current)
if last != current:
unchanged_count = 0
last = current
else:
unchanged_count += 1
if unchanged_count > MAX_UNCHANGE_COUNT:
break
state = STATE_INIT_PULL_DOWN
lengths = []
current_length = 0
for current in data:
current_length += 1
if state == STATE_INIT_PULL_DOWN:
if current == GPIO.LOW:
state = STATE_INIT_PULL_UP
else:
continue
if state == STATE_INIT_PULL_UP:
if current == GPIO.HIGH:
state = STATE_DATA_FIRST_PULL_DOWN
else:
continue
if state == STATE_DATA_FIRST_PULL_DOWN:
if current == GPIO.LOW:
state = STATE_DATA_PULL_UP
else:
continue
if state == STATE_DATA_PULL_UP:
if current == GPIO.HIGH:
current_length = 0
state = STATE_DATA_PULL_DOWN
else:
continue
if state == STATE_DATA_PULL_DOWN:
if current == GPIO.LOW:
lengths.append(current_length)
state = STATE_DATA_PULL_UP
else:
continue
if len(lengths) != 40:
return False
shortest_pull_up = min(lengths)
longest_pull_up = max(lengths)
halfway = (longest_pull_up + shortest_pull_up) / 2
bits = []
the_bytes = []
byte = 0
for length in lengths:
bit = 0
if length > halfway:
bit = 1
bits.append(bit)
for i in range(0, len(bits)):
byte = byte << 1
if (bits[i]):
byte = byte | 1
else:
byte = byte | 0
if ((i + 1) % 8 == 0):
the_bytes.append(byte)
byte = 0
checksum = (the_bytes[0] + the_bytes[1] + the_bytes[2] + the_bytes[3]) & 0xFF
if the_bytes[4] != checksum:
return False
return the_bytes[0], the_bytes[2]
def main():
print("启动从GPIO获取温湿度信息，并写入h2db的程序")
driver = 'org.h2.Driver'
url = 'jdbc:h2:tcp://172.16.10.213:9123/mem:kuradb;DB_CLOSE_DELAY=-1'
username = 'sa'
password = ''
originSql = 'insert into telemetry(temperature, humidity) values(%.2f, %.2f)'
jar = '/jiguiquan/h2-1.4.200.jar'
conn = jaydebeapi.connect(driver, url, [username, password], jar)
curs = conn.cursor()
try:
while True:
result = read_dht11_dat()
if result:
humidity, temperature = result
insertSql = originSql % (temperature, humidity / float(100))
curs.execute(insertSql)
if curs.rowcount > 0:
print("本轮插入h2db成功，温度为：%.2f，湿度为：%.2f" % (temperature, humidity / float(100)))
else:
print("本轮插入h2db失败，温度为：%.2f，湿度为：%.2f" % (temperature, humidity / float(100)))
time.sleep(1)
finally:
curs.close()
conn.close()
def destroy():
GPIO.cleanup()
if __name__ == '__main__':
try:
main()
except KeyboardInterrupt:
destroy()
4、要想运行的上面的python程序，需要我们安装一些依赖：
# 检查一下环境 root@raspberrypi:~# python -V Python 3.9.2 root@raspberrypi:~# pip -V pip 20.3.4 from /usr/lib/python3/dist-packages/pip (python 3.9) ## 安装RPi.GPIO root@raspberrypi:~# pip install RPi.GPIO ## 安装jaydebeapi root@raspberrypi:~# pip install jaydebeapi
5、由于使用的jdbc连接h2db，所以还需要使用到连接h2的jar包：
root@raspberrypi:/jiguiquan# pwd /jiguiquan root@raspberrypi:/jiguiquan# ls h2-1.4.200.jar jiguiquan.py
6、在h2db数据库中创建我们需要的telemetry表：
CREATE TABLE telemetry(id INTEGER AUTO_INCREMENT PRIMARY KEY, temperature DOUBLE, humidity DOUBLE, ts timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP);
7、nohup运行jiguiquan.py，并查看日志：
nohup python -u jiguiquan.py > jiguiquan.log 2>&1 & # 因为python的输出有缓冲，导致nohup.out并不能够马上看到输出，所以我们可以通过 -u关闭python缓冲！ ## 查看nohup日志： root@raspberrypi:/jiguiquan# tail -f -n 50 jiguiquan.log 启动从GPIO获取温湿度信息，并写入h2db的程序 本轮插入h2db成功，温度为：25.00，湿度为：0.46 本轮插入h2db成功，温度为：25.00，湿度为：0.46 本轮插入h2db成功，温度为：25.00，湿度为：0.46
8、我们去h2db数据库看看，数据是否写入成功：
有些时候，我们为了节约h2db的存储空间，还可以使用update代替insert！
update telemetry set temperature= %.2f, humidity = %.2f, ts = CURRENT_TIMESTAMP where id =1;
