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Raspbery Pi Analog Input with MCP3008
#!/usr/bin/env python
# Written by Limor "Ladyada" Fried for Adafruit Industries, (c) 2015
# This code is released into the public domain
import time
import os
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
DEBUG = 1
# read SPI data from MCP3008 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 = 18
SPIMISO = 23
SPIMOSI = 24
SPICS = 25
# 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 move
trim_pot_changed = False
# read the analog pin
trim_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_pot
print "pot_adjust:", pot_adjust
print "last_read", last_read
if ( pot_adjust > tolerance ):
trim_pot_changed = True
if DEBUG:
print "trim_pot_changed", trim_pot_changed
if ( trim_pot_changed ):
set_volume = trim_pot / 10.24 # convert 10bit adc0 (0-1024) trim pot read into 0-100 volume level
set_volume = round(set_volume) # round out decimal value
set_volume = int(set_volume) # cast volume as integer
print '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 volume
if DEBUG:
print "set_volume", set_volume
print "tri_pot_changed", set_volume
# save the potentiometer reading for the next loop
last_read = trim_pot
# hang out and do nothing for a half second
time.sleep(0.5)
@Muuo
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Muuo commented Feb 11, 2013

I'm assuming that

adcout >>= 1 # first bit is 'null' so drop it

is a erroneously commented correction for the mistake mentioned by ChickenProp above

@naikrovek
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Why aren't you using the SPI hardware? raspi-config can enable it, so it's not hard. It's easy to use from C, and I HATE C. Bit banging SPI doesn't teach anyone how to use SPI, IMHO.

@ralfiii
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ralfiii commented Apr 10, 2015

Has anyone ported the code to use the SPI interface?
Thank,
Ralf

@luxedo
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luxedo commented Nov 23, 2015

Hey guys!
take a look at my library that uses SpiDev to communicate with the chip.

@haydenroche5
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haydenroche5 commented Aug 13, 2016

Reviving this because I think the issue ChickenProp raised in 2012 still remains. Reading 12 bits in that loop is indeed 1 too many, and a right shift or, equivalently, division by 2 is misleading, as is the comment that this is a "null" bit. As someone learning about SPI, this mysterious shift confused me for 2 solid days. The empty bit is already on the bus after the command, as ChickenProp states, so you only need to read out 11 bits: 1 null and 10 valid ADC bits. Sure, you can read the additional bit and shift it out after, but what's the point?

@chiques
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chiques commented Jun 1, 2017

You have to follow these instructions or else the account blocks the script.

"> If the tips above didn't help, visit https://www.google.com/accounts/DisplayUnlockCaptcha and follow the steps on the page."

@thijstriemstra
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Can you make the print statements compatible with Python 2.7/3.x?

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