adafruit_mcp3008.py
====================
#!/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)
====================