长夜漫漫,不再黑暗

Byamber

长夜漫漫,不再黑暗

Overview

光敏电阻是是利用光电导效应的一种特殊的电阻,它的电阻和光线的强弱有直接关系,光强度增加,则电阻减小;光强度减小,则电阻增大。利用这一特性可以做很多东西,比如照相机、草坪灯、声光控开关、路灯自动开关等。本项目我们在树莓派上用光敏电阻、继电器等器件完成路灯自动开关制作。当光照比较暗的时候继电器闭合点亮LED灯;光照变亮的时候,继电器断开,LED熄灭。

DSC_5460

Parts

LACC2006ADx3
光敏电阻 x1
PI
Pi3 x1
LACC2006AD-24
LED x1
BMP180
继电器 x1
LACC2006AD-26
10K电阻 x1
LACC2006AD-26
1K电阻 x1
LACC2006AD-31
跳线若干
LACC2006AD-12
面包板 x1
MCP3008
MCP2008 x1
(MCP3204 x1)

Hardware

Raspberry Pi是一个出色的微型计算机,你可以使用它来控制数字输入和输出。但是当你想用它来处理模拟信号,例如像热敏电阻、电位器等模拟传感器输出时候,Raspberry Pi就有些力不从心了,就需要借助模数转换芯片将模拟信号转换成数字信号。本项目中利用MCP3008(or MCP3204)把光敏电阻输出的电压信号转换成数字信号,Pi根据转换后的数值大小控制继电器通断,从而控制灯亮灭。MCP3008是一款8通道10位精度的模数转换芯片;MCP3204是一款4通道12位精度的模数装换芯片。一路继电器模块是高电平有效,即控制器(Pi)给继电器一个高电平,继电器导通,继电器模块上的LED指示灯亮起;低电平断开,继电器模块上的LED指示灯灯熄灭。

MCP3008接线图:

Untitled Sketch_MCP3008

MCP3204接线图:

Untitled Sketch_MCP32041

Software

(1)在开始编写程序前需要对我们的树莓派Python库文件进行安装设置,此处要用到GPIO库,先安装GPIO库,打开终端,更新apt-get软件安装包列表(注意必须要在网络连接正常情况下),然后执行安装命令来安装raspberry-gpio-python包(如果已经安装请跳过此步),具体指令如下:

1)更新源

pi@raspberrypi ~ $ sudo apt-get update

2)安装python

pi@raspberrypi ~ $ sudo apt-get install python-dev

 

3)安装python-pip(python-pip是一个管理python软件包的工具)

pi@raspberrypi ~ $ sudo apt-get install python-pip

4)利用pip安装rpi.gpio

pi@raspberrypi ~ $ sudo pip install rpi.gpio

(2)测试是否安装成功

图片4

通过上述几个步骤,已经安装好了Python与树莓派外置硬件GPIO库文件,在接下来的程序里就可以直接调用代码了。

(3)编写代码

你可以将Pi接到一台显示器上编写代码,也可以通过SSH连接到你的Pi编写代码

1)在Pi中任一目录下(如/home/pi/)新建一个led.py文件

pi@raspberrypi ~ $ sudo touch raspi-adc-photo.py

2)打开raspi-adc-photo.py文件

pi@raspberrypi ~ $ sudo nano raspi-adc-photo.py

3)向raspi-adc-photo.py中写入如下代码

import time      #importing the time module
import os     #importing the os module
import RPi.GPIO as GPIO       #importing the RPi.GPIO module
GPIO.cleanup()      #clean up at the end of your script
GPIO.setmode(GPIO.BCM)    #to specify whilch pin numbering system

#read SPI data from MCP3008(or MCP3204) chip,8 possible adc's (0 thru 7)
def readadc(adcnum, clockpin, mosipin, misopin, cspin):
        if ((adcnum > 7) or (adcnum < 0)):
                return -1
        GPIO.output(cspin, True)  

        GPIO.output(clockpin, False)  # start clock low
        GPIO.output(cspin, False)     # bring CS low

        commandout = adcnum
        commandout |= 0x18  # start bit + single-ended bit
        commandout <<= 3    # we only need to send 5 bits here
        for i in range(5):
                if (commandout & 0x80):
                        GPIO.output(mosipin, True)
                else:
                        GPIO.output(mosipin, False)
                commandout <<= 1
                GPIO.output(clockpin, True)
                GPIO.output(clockpin, False)

        adcout = 0
        # read in one empty bit, one null bit and 10 ADC bits
        for i in range(12):
                GPIO.output(clockpin, True)
                GPIO.output(clockpin, False)
                adcout <<= 1
                if (GPIO.input(misopin)):
                        adcout |= 0x1

        GPIO.output(cspin, True)
        
        adcout >>= 1       # first bit is 'null' so drop it
        return adcout

# change these as desired - they're the pins connected from the
# SPI port on the ADC to the Cobbler
SPICLK = 11
SPIMISO = 9
SPIMOSI = 10
SPICS = 8

# set up the SPI interface pins
GPIO.setup(SPIMOSI, GPIO.OUT)
GPIO.setup(SPIMISO, GPIO.IN)
GPIO.setup(SPICLK, GPIO.OUT)
GPIO.setup(SPICS, GPIO.OUT)

#relay port to the cobbler
Relay_pin = 26

#set up the relay port
GPIO.setup(Relay_pin,GPIO.OUT)
 
#disable the gpio warning information
GPIO.setwarnings(False)

# photoresistor connected to adc #0
photo_ch = 0;

#last_read = 0       # this keeps track of the last potentiometer value
#tolerance = 5       # to keep from being jittery we'll only change
                    # volume when the pot has moved more than 5 'counts'
print"______________________________________________________________________"
while True:
  photo_value = readadc(photo_ch, SPICLK, SPIMOSI, SPIMISO, SPICS)
  if(photo_value<=300):
    print "It`s dark,turn on the light"
    GPIO.output(Relay_pin,True)
  else:
    print "dawn,turn off the light"
    GPIO.output(Relay_pin,False)

  print "photo_value=", photo_value
  time.sleep(0.5)

#GPIO.cleanup()

也可以通过如下命令下载得到:

4)保存退出

编写完程序后,键盘输入”Ctrl X”,提示是否保存退出,键入Y然后回车就可以保存退出了

2017-03-14-102304_1824x984_scrot

(5)运行程序,查看效果

pi@raspberrypi ~ $ sudo python ./raspi-adc-photo.py

2017-03-14-102441_1824x984_scrot用手遮住光敏电阻可以听到继电器闭合声,灯亮起;用光照着光敏电阻,也能听到继电器断开的声音,灯熄灭。

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