树莓派3+温度传感器+伺服电机

Question

我有树莓派 3 并尝试创建智能温室模型。如果温度过高，此模型应打开窗口。

我是新人用Python写代码，找了几个例子：1.温度传感器和2.伺服电机旋转。

谁能帮我用伺服电机？例如，如果温度为 20°C，我想将伺服移动到 30°，如果是 21°C，则移动 40° 伺服等等。

我有 Python 代码：

import sys
import Adafruit_DHT
import time
import wiringpi
sensor_args = { '11': Adafruit_DHT.DHT11,
            '22': Adafruit_DHT.DHT22,
            '2302': Adafruit_DHT.AM2302 }
if len(sys.argv) == 3 and sys.argv[1] in sensor_args:
  sensor = sensor_args[sys.argv[1]]
  pin = sys.argv[2]
else:
  print('usage: sudo ./Adafruit_DHT.py [11|22|2302] GPIOpin#')
  print('example: sudo ./Adafruit_DHT.py 2302 4 - Read from an AM2302 
  connected to GPIO #4')
  sys.exit(1)


humidity, temperature = Adafruit_DHT.read_retry(sensor, pin)

if humidity is not None and temperature is not None:
  print('Temp={0:0.1f}*  Humidity={1:0.1f}%'.format(temperature, humidity))
else:
  print('Failed to get reading. Try again!')
  sys.exit(1)

temp=temperature
text_file = open("output.txt", "w")
text_file.write("%s" %(temp))
text_file.close()

wiringpi.wiringPiSetupGpio()
wiringpi.pinMode(18,wiringpi.GPIO.PWM_OUTPUT)
wiringpi.pwmSetMode(wiringpi.GPIO.PWM_MODE_MS)

wiringpi.pwmSetClock(192)
wiringpi.pwmSetRange(2000)
delay_period = 0.01

while temp==20.0:
  for pulse in range(50,250,1):
    wiringpi.pwmWrite(18,50)
    time.sleep(delay_period)

for pulse in range(250,50,-1):
    wiringpi.pwmWrite(18,pulse)
    time.sleep(delay_period)

关于伺服电机的部分我在互联网上找到的示例。我需要将“while”替换为“if”。我自己试过，但转子一直旋转到相同的角度。 谁能帮我处理这小部分代码？

第二个问题，如何在树莓派上的终端“sudo python server.py 11 17”中每 10 分钟自动运行此命令，并且在树莓派打开时自动运行？

感谢您的帮助！

Answer 1

脉冲是您在代码中控制伺服位置的方式：

wiringpi.pwmWrite(18,pulse)

看这个例子： https://learn.adafruit.com/adafruits-raspberry-pi-lesson-8-using-a-servo-motor?view=all

根据您的舵机，100 的脉冲值将舵机一直向左移动（在本例中关闭），200 一直向右移动（在本例中打开）。您需要通过阅读数据表或通过实验找到这些值。一旦你有了这些，你将如何设置伺服的位置：

min_servo_val = 100 
max_servo_val = 200

wiringpi.pwmWrite(18, min_servo_val) # Move all the way left
time.sleep(1) # Wait a second
wiringpi.pwmWrite(18, max_servo_val) # Move all the way right

现在您可以编写一个函数，将温度转换为 min_servo_val 和 max_servo_val 之间的伺服位置，或者使用简单的 if 语句。这是将温度转换为脉冲（伺服位置）的函数示例：

def get_servo_position(temp):

    min_servo_val = 100 # Pulse value at which window is all the way closed closed
    max_servo_val = 200 # Pulse value at which window is all the way open


    full_closed_temp = 20.0 # Temperature at which window is completely closed
    full_open_temp = 26.0 # Temperature at which window is completely open

    if temp <= full_closed_temp:
        return min_servo_val
    elif temp >= full_open_temp:
        return max_servo_val
    else:
        return ((temp - full_closed_temp) / (full_open_temp - full_closed_temp)) * (max_servo_val - min_servo_val) + min_servo_val

现在你可以这样做了：

print get_servo_position(19) # 100 all the way closed

print get_servo_position(22) # 133.3, or 33% of the way between min_servo_val and max_servo_val

print get_servo_position(25) # 183.3, or 83% of the way between min_servo_val and max_servo_val

print get_servo_position(27) # 200 all the way open

现在您需要一个循环，每十分钟检查一次温度并调整伺服位置。像这样的：

while True:
    humidity, temp = Adafruit_DHT.read_retry(sensor, pin) # Get temperature.
    position = get_servo_position(temp) # Get the servo position
    wiringpi.pwmWrite(18,position) # Move to the position
    time.sleep(10*60) # Wait 10 minutes

把它们放在一起，你的脚本应该看起来像这样：

import sys
import Adafruit_DHT
import time
import wiringpi

dht_pin = 17 # GPIO conencted to DHT
servo_pin = 18 # GPIO connected to servo

dht_sensor = Adafruit_DHT.DHT11 # Put your sensor here, or set it from command line args 


min_servo_val = 100 # Pulse value at which window is all the way closed closed
max_servo_val = 200 # Pulse value at which window is all the way open


full_closed_temp = 20.0 # Temperature at which window is completely closed
full_open_temp = 26.0 # Temperature at which window is completely open


def get_servo_position(temp):

    if temp <= full_closed_temp:
        return min_servo_val
    elif temp >= full_open_temp:
        return max_servo_val
    else:
        return ((temp - full_closed_temp) / (full_open_temp - full_closed_temp)) * (max_servo_val - min_servo_val) + min_servo_val


def main_loop():
    while True:
        humidity, temp = Adafruit_DHT.read_retry(dht_sensor, dht_pin) # Get temperature.
        position = get_servo_position(temp) # Get the servo position
        wiringpi.pwmWrite(18,position) # Move to the position
        time.sleep(10*60) # Wait 10 minutes


if __name__ == '__main__':
    # If you need to get command line arguments, do it below, otherwise just set the pins and other settings at the top of this script.

    # For example...
    # dht_pin = sys.argv[1] 
    # servo_pin = sys.argv[2]


    # Set up servo
    wiringpi.wiringPiSetupGpio()
    wiringpi.pinMode(18,wiringpi.GPIO.PWM_OUTPUT)
    wiringpi.pwmSetMode(wiringpi.GPIO.PWM_MODE_MS)

    wiringpi.pwmSetClock(192)
    wiringpi.pwmSetRange(2000)

    # Enter main loop
    main_loop()

请注意，我遗漏了命令行参数解析。如果你需要这些，你可以在if __name__ == '__main__':之后添加它们

最后，让脚本在启动时运行是一个很好的话题： Start shell script on Raspberry Pi startup