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import spidev
import time
import os
DEBUG = 0
spi = spidev.SpiDev()
spi.open(0,0)
# read SPI data from MCP3008 chip, 8 possible adc's (0 thru 7)
def readadc(adcnum):
if ((adcnum > 7) or (adcnum < 0)):
return -1
r = spi.xfer2([1,(8+adcnum)<<4,0])
adcout = ((r[1]&3) << 8) + r[2]
return adcout
# 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)
# 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)