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[教程] 在树莓派上面使用 MCP3424 18位AD转换模块

前段时间在DFRobot的用户群里面有个用户用到了这个模块:
他想要一个中文的教程, 在LZ的努力下, 终于跑通了.
1. 安装最新的树莓派镜像, 可以参考这个帖子:
2. 然后进行连线的工作 (MCP3424上面的编码器全部拨到ON的一侧)
在树莓派上面使用 MCP3424 18位AD转换模块图1

MCP3424 GND >> 树莓派 Ground
MCP3424 +5V >> 树莓派 DC Power 5V
MCP3424 SCL >> 树莓派 GPIO03(SCL1, I2C)
MCP3424 SDA >> 树莓派 GPIO02(SDA1, I2C)
MCP3424 C*+ 和 C*- 接上对应需要测电压的两端.

3. 首先要启用I2C接口功能,

打开Terminal.
键入
```
sudo raspi-config
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```
用上下键选择 5 Interfacing Options , 按回车进入.
选择 5 I2C , 按回车确认.(需要重启)

4. 安装Python依赖库(树莓派需要联网)

更新包
```
sudo apt-get update
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```
安装包
```
sudo apt-get install build-essential libi2c-dev i2c-tools python-dev libffi-dev
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```
安装Python包(最新的0.3.4会出现依赖问题, 这里使用了0.3.3版)
```
pip install MCP342x==0.3.3
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```

5. 运行下面的Python脚本就可以了:

#!/usr/bin/env python

import glob
import logging
import smbus
from MCP342x import MCP342x

import numpy as np


__author__ = 'Steve Marple'
__version__ = '0.3.3'
__license__ = 'MIT'


def get_smbus():
    candidates = []
    prefix = '/dev/i2c-'
    for bus in glob.glob(prefix + '*'):
        try:
            n = int(bus.replace(prefix, ''))
            candidates.append(n)
        except:
            pass

    if len(candidates) == 1:
        return smbus.SMBus(candidates[0])
    elif len(candidates) == 0:
        raise Exception("Could not find an I2C bus")
    else:
        raise Exception("Multiple I2C busses found")


logging.basicConfig(level='DEBUG')

logger = logging.getLogger(__name__)

bus = get_smbus()

# Create objects for each signal to be sampled
addr68_ch0 = MCP342x(bus, 0x68, channel=0, resolution=18)
addr68_ch1 = MCP342x(bus, 0x68, channel=1, resolution=18)
addr68_ch2 = MCP342x(bus, 0x68, channel=2, resolution=18)
addr68_ch3 = MCP342x(bus, 0x68, channel=3, resolution=16)

# Create a list of all the objects. They will be sampled in this
# order, unless any later objects can be sampled can be moved earlier
# for simultaneous sampling.
adcs = [addr68_ch0, addr68_ch1, addr68_ch2, addr68_ch3]
r = MCP342x.convert_and_read_many(adcs, samples=2)
print('return values: ')
print(r)


# , scale_factor=2.448579823702253
addr68_ch0.convert()
print(addr68_ch3.convert_and_read())
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