树莓派基础实验17：温度传感器实验

#!/usr/bin/env python
#------------------------------------------------------
#
#       您可以使用下面语句将此脚本导入另一个脚本：
#           “import PCF8591 as ADC”                
#   
#   ADC.Setup(Address)  # 查询PCF8591的地址：“sudo i2cdetect -y 1”
# i2cdetect  is  a  userspace  program to scan an I2C bus for devices.
# It outputs a table with the list of detected devices on the specified bus.
#   ADC.read(channal)   # Channal范围从0到3 
#   ADC.write(Value)    # Value范围从0到255
#
#------------------------------------------------------
#SMBus (System Management Bus,系统管理总线) 
import smbus   #在程序中导入“smbus”模块
import time

# for RPI version 1, use "bus = smbus.SMBus(1)"
# 0 代表 /dev/i2c-0， 1 代表 /dev/i2c-1 ,具体看使用的树莓派那个I2C来决定
bus = smbus.SMBus(1)         #创建一个smbus实例

#在树莓派上查询PCF8591的地址：“sudo i2cdetect -y 1”
def setup(Addr):
    global address
    address = Addr

def read(chn): #channel
    if chn == 0:
        bus.write_byte(address,0x40)   #发送一个控制字节到设备
    if chn == 1:
        bus.write_byte(address,0x41)
    if chn == 2:
        bus.write_byte(address,0x42)
    if chn == 3:
        bus.write_byte(address,0x43)
    bus.read_byte(address)         # 从设备读取单个字节，而不指定设备寄存器。
    return bus.read_byte(address)  #返回某通道输入的模拟值A/D转换后的数字值

def write(val):
    temp = val  # 将字符串值移动到temp
    temp = int(temp) # 将字符串改为整数类型
    # print temp to see on terminal else comment out
    bus.write_byte_data(address, 0x40, temp) 
    #写入字节数据，将数字值转化成模拟值从AOUT输出

if __name__ == "__main__":
    setup(0x48) 
 #在树莓派终端上使用命令“sudo i2cdetect -y 1”，查询出PCF8591的地址为0x48
    while True:
        print '电位计   AIN0 = ', read(0)   #电位计模拟信号转化的数字值
        print '光敏电阻 AIN1 = ', read(1)   #光敏电阻模拟信号转化的数字
        print '热敏电阻 AIN2 = ', read(2)   #热敏电阻模拟信号转化的数字值
        tmp = read(0)
        tmp = tmp*(255-125)/255+125 
# 125以下LED不会亮，所以将“0-255”转换为“125-255”，调节亮度时灯不会熄灭
        write(tmp)
        time.sleep(2)

#!/usr/bin/env python
import PCF8591 as ADC
import RPi.GPIO as GPIO
import time
import math

DO = 17
GPIO.setmode(GPIO.BCM)

def setup():
    ADC.setup(0x48)
    GPIO.setup(DO, GPIO.IN)

def Print(x):
    if x == 1:
        print ''
        print '***********'
        print '* Better~ *'
        print '***********'
        print ''
    if x == 0:
        print ''
        print '************'
        print '* Too Hot! *'
        print '************'
        print ''

def loop():
    status = 1
    tmp = 1
    while True:
        analogVal = ADC.read(0)   #温度传感器模拟输出A/D转化后的数字值
        Vr = 5 * float(analogVal) / 255   #Vr为数字值转化为热敏电阻的原始模拟电压值
        Rt = 10000 * Vr / (5 - Vr)   
        #Rt是热敏电阻在T1温度下的阻值,10000=10k为与热敏电阻串联的电阻的阻值
        #查阅传感器电路图知，因为是串联，所以电流值相等 Vr/Rt=(5-Vr)/10000

        temp = 1/(((math.log(Rt / 10000)) / 3950) + (1 / (273.15+25)))
        # T1=1/（ln（Rt/R）/B+1/T2） 对应的摄氏温度t=T1-273.15 
        # R=10k=10000 B=3950 T2=(273.15+25)
        temp = temp - 273.15
        print 'temperature = ', temp, 'C'


        if temp > 33:
            tmp = 0;
        elif temp < 31:
            tmp = 1;
        

        if tmp != status:
            Print(tmp)
            status = tmp

        time.sleep(0.2)

if __name__ == '__main__':
    try:
        setup()
        loop()
    except KeyboardInterrupt: 
        pass