BakeBit - Light Sensor/zh

English

1 介绍

Light Sensor

• BakeBit - Light Sensor是一个光敏电阻模块，主要器件是一个光敏电阻。光敏电阻的制作材料具有在特定波长的光照射下，其阻值迅速减小的特性。
• 这是由于光照产生的载流子都参与导电，在外加电场的作用下作漂移运动，电子奔向电源的正极，空穴奔向电源的负极，从而使光敏电阻器的阻值迅速下降。在电源激励下，输出端分压减小。

2 特性

• 使用标准的2.0mm 4 Pin BakeBit接口
• PCB尺寸（mm）：20x24
• 模拟信号输出

• 引脚说明:

名称	描述
GND	地
5V	电源5V
NC	空
SIG	信号

3 示例程序：Smart Lighting

利用亮度传感器，聪明地控制灯光(灯用LED Bar来模拟)，环境越暗就让灯越亮，环境亮度足够时，就将灯变暗或者熄灭。 本示例需要配合BakeBit - LED Bar使用。

3.1 硬件连接

简单的将BakeBit - LED Bar模块插入 D3 接口，将BakeBit - Light Sensor插入 A0 接口，如下面这样：

3.2 示例源代码

import time
import bakebit
 
# Connect the BakeBit Light Sensor to analog port A0
# SIG,NC,VCC,GND
light_sensor = 0
 
# Connect the BakeBit LED Bar to digital port D3
# DI,DCKI,VCC,GND
ledbar = 3
 
 
lowThreshold = 500
highTreshold = 600
 
bakebit.pinMode(light_sensor,"INPUT")
bakebit.pinMode(ledbar,"OUTPUT")
time.sleep(.2)
bakebit.bakeBitLedBar_Init(ledbar, 0, 5)
time.sleep(.5)
old_color = 0
 
while True:
    try:
        light_count = 0
 
        # Get sensor value
        sensor_value = bakebit.analogRead(light_sensor)
        if sensor_value > highTreshold:
            f=(1023-highTreshold)/4
            light_count =  (sensor_value-highTreshold)/f+1
 
            # turn on ledbar
            color16bit = bakebit.Green
            if light_count > 1:
                color16bit = color16bit | (bakebit.Green << 3)
            if light_count > 2:
                color16bit = color16bit | (bakebit.Green << 6)
            if light_count > 3:
                color16bit = color16bit | (bakebit.Green << 9)
            if light_count > 4:
                color16bit = 0
                color16bit = color16bit | bakebit.Blue
                color16bit = color16bit | (bakebit.Blue << 3)
                color16bit = color16bit | (bakebit.Blue << 6)
                color16bit = color16bit | (bakebit.Blue << 9)
                color16bit = color16bit | (bakebit.Blue << 12)
 
            if color16bit != old_color:
                old_color = color16bit
                lowBits = color16bit & 255
                highBits = (color16bit & (255 << 8)) >> 8
                bakebit.bakeBitLedBar_Show(ledbar, highBits, lowBits)
 
        elif sensor_value < lowThreshold:
            # turn off ledbar
            bakebit.bakeBitLedBar_Show(ledbar, 0, 0)
 
        print("sensor_value = %d light_count =%d" %(sensor_value,  light_count))
        time.sleep(.5)
 
    except KeyboardInterrupt:
        bakebit.bakeBitLedBar_Release(ledbar)
        time.sleep(.2)
        break
    except IOError:
        print ("Error")

Github

3.3 运行示例

假设你已经参考bakebit教程安装了BakeBit源代码，
要运行示例程序，可以在开发板上进入 BakeBit/Software/Python目录,运行bakebit_prj_SmartLighting.py:

cd ~/BakeBit/Software/Python
sudo python bakebit_prj_SmartLighting.py

3.4 运行结果

测试时可用物品盖住光敏电阻模拟环境变暗，或者用手机电筒照射模拟环境变亮，然后观察LED Bar的变化。
LED Bar上被点亮的LED个数由当前环境的光线决定，越暗，被点亮的就最多。

4 相关资料

• [Schematic](BakeBit - Light Sensor.pdf)
• [BakeBit Github项目](https://github.com/friendlyarm/BakeBit)
• [BakeBit Starter Kit手册](http://wiki.friendlyarm.com/bakebit/bakebit_starter_kit_manual_cn.pdf)