树莓派基础实验16：霍尔传感器实验

#!/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 RPi.GPIO as GPIO
import PCF8591 as ADC
import time

HallPin = 11
Gpin   = 13
Rpin   = 12

def setup():
    ADC.setup(0x48)
    GPIO.setmode(GPIO.BOARD)       # Numbers GPIOs by physical location
    GPIO.setup(Gpin, GPIO.OUT)     # Set Green Led Pin mode to output
    GPIO.setup(Rpin, GPIO.OUT)     # Set Red Led Pin mode to output
    GPIO.setup(HallPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)    # Set BtnPin's mode is input, and pull up to high level(3.3V)
    GPIO.add_event_detect(HallPin, GPIO.BOTH, callback=detect, bouncetime=200)
#    检测到磁场时，数字输出低电平，即GPIO.input(HallPin)==0 
#没有检测到磁场时，数字输出高电平，即GPIO.input(HallPin)==1

def Led(x):
    if x == 0:    #检测到磁场时，亮红灯
        GPIO.output(Rpin, 1)
        GPIO.output(Gpin, 0)
    if x == 1:    #没有检测到磁场时，亮绿灯
        GPIO.output(Rpin, 0)
        GPIO.output(Gpin, 1)

def Print1(x):
    if x == 0:    #检测到磁场时，数字输出低电平，x==0
        print '    ***********************************'
        print '    *   Detected magnetic materials   *'
        print '    ***********************************'

def detect(chn):  
    Led(GPIO.input(HallPin))
    Print1(GPIO.input(HallPin))


def Print2(x):
    if x == 1:
        print ''
        print '*************'
        print '* No Magnet *'
        print '*************'
        print ''
    if x == 0:
        print ''
        print '*************'
        print '* Detected Magnet *'
        print '*************'
        print ''


def loop():
    status = 0
    while True:
        res = ADC.read(0)      #模拟输出信号A/D转换后的数字信号值
        print 'Current intensity of magnetic field : ', res
        if res  < 10:  #这里的数字输出ADC.read(0)只有两个值，0或255
            tmp = 0    #ADC.read(0)为255时没有检测到磁场
                       #ADC.read(0)为 0 时检测到磁场，但有少量误差的其它值，比如1或254等值偶尔出现
        if res > 200:  
            tmp = 1
        if tmp != status:
            Print2(tmp)
            status = tmp
        time.sleep(0.5)

def destroy():
    GPIO.output(Gpin, GPIO.LOW)       # Green led off
    GPIO.output(Rpin, GPIO.LOW)       # Red led off
    GPIO.cleanup()                     # Release resource

if __name__ == '__main__':
    setup()
    try:
        loop()
    except KeyboardInterrupt:  # When 'Ctrl+C' is pressed, the child program destroy() will be  executed.
        destroy()