mcp3208 和 树莓派3b板子的配置以及对应代码

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先上连接图。

MCP3208 在2013年一位日本大佬的代码：
https://seinzumtode.hatenadiary.jp/entry/20130918/1379501130
针对MQ-X这类气体模块，用MQ-2去做实验(这个模块是可燃气体，那个打火机就能看出程序里的读数变化)。所以MQ2的AO的小针就是对应MCP3208上面的CH0的。
最后 如果再修改的好一点的话，关于pot move的这类代码其实在气体模块这里是用不到的，然后volume的意义针对气体模块其实应该重新整理公式去换算。

import time
import os
import RPi.GPIO as GPIOGPIO.setmode(GPIO.BCM)
DEBUG = 1# read SPI data from MCP3208 chip, 8 possible adc's (0 thru 7)
def readadc(adcnum, clockpin, mosipin, misopin, cspin):if ((adcnum > 7) or (adcnum < 0)):return -1GPIO.output(cspin, True)GPIO.output(clockpin, False)  # start clock lowGPIO.output(cspin, False)     # bring CS lowcommandout = adcnumcommandout |= 0x18  # start bit + single-ended bitcommandout <<= 3    # we only need to send 5 bits herefor i in range(5):if (commandout & 0x80):GPIO.output(mosipin, True)else:GPIO.output(mosipin, False)commandout <<= 1GPIO.output(clockpin, True)GPIO.output(clockpin, False)adcout = 0# read in one empty bit, one null bit and 10 ADC bitsfor i in range(12):GPIO.output(clockpin, True)GPIO.output(clockpin, False)adcout <<= 1if (GPIO.input(misopin)):adcout |= 0x1GPIO.output(cspin, True)adcout >>= 1       # first bit is 'null' so drop itreturn adcout# change these as desired - they're the pins connected from the
# SPI port on the ADC to the Cobbler
#SPICLK = 18
#SPIMISO = 23
#SPIMOSI = 24
#SPICS = 25
# Above pin number seems not working. I modified the pin as below.
# See also: http://elinux.org/RPi_Low-level_peripherals
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)# 10k trim pot connected to adc #0
potentiometer_adc = 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'while True:# we'll assume that the pot didn't movetrim_pot_changed = False# read the analog pintrim_pot = readadc(potentiometer_adc, SPICLK, SPIMOSI, SPIMISO, SPICS)# how much has it changed since the last read?pot_adjust = abs(trim_pot - last_read)if DEBUG:print "trim_pot:", trim_potprint "pot_adjust:", pot_adjustprint "last_read", last_readif ( pot_adjust > tolerance ):trim_pot_changed = Trueif DEBUG:print "trim_pot_changed", trim_pot_changedif ( trim_pot_changed ):# convert 12bit adc0 (0-4096) trim pot read into 0-100 volume levelset_volume = trim_pot / (10.24 * 4)set_volume = round(set_volume)          # round out decimal valueset_volume = int(set_volume)            # cast volume as integerprint 'Volume = {volume}%' .format(volume = set_volume)set_vol_cmd = 'sudo amixer cset numid=1 -- {volume}% > /dev/null' .format(volume = set_volume)os.system(set_vol_cmd)  # set volumeif DEBUG:print "set_volume", set_volumeprint "tri_pot_changed", set_volume# save the potentiometer reading for the next looplast_read = trim_pot# hang out and do nothing for a half secondtime.sleep(0.5)

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