The following code can be downloaded directly to your Raspberry Pi. It will read the trimpot value, translate the reading to a volume range and modify the OS output volume level on your Raspberry Pi.
The remap_range() method is being used to convert the 16-bit analog in range 0 - 65,535 to volume 0-100%.
# SPDX-FileCopyrightText: 2019 Mikey Sklar for Adafruit Industries
#
# SPDX-License-Identifier: MIT
import os
import time
import busio
import digitalio
import board
import adafruit_mcp3xxx.mcp3008 as MCP
from adafruit_mcp3xxx.analog_in import AnalogIn
# create the spi bus
spi = busio.SPI(clock=board.SCK, MISO=board.MISO, MOSI=board.MOSI)
# create the cs (chip select)
cs = digitalio.DigitalInOut(board.D22)
# create the mcp object
mcp = MCP.MCP3008(spi, cs)
# create an analog input channel on pin 0
chan0 = AnalogIn(mcp, MCP.P0)
print('Raw ADC Value: ', chan0.value)
print('ADC Voltage: ' + str(chan0.voltage) + 'V')
last_read = 0 # this keeps track of the last potentiometer value
tolerance = 250 # to keep from being jittery we'll only change
# volume when the pot has moved a significant amount
# on a 16-bit ADC
def remap_range(value, left_min, left_max, right_min, right_max):
# this remaps a value from original (left) range to new (right) range
# Figure out how 'wide' each range is
left_span = left_max - left_min
right_span = right_max - right_min
# Convert the left range into a 0-1 range (int)
valueScaled = int(value - left_min) / int(left_span)
# Convert the 0-1 range into a value in the right range.
return int(right_min + (valueScaled * right_span))
while True:
# we'll assume that the pot didn't move
trim_pot_changed = False
# read the analog pin
trim_pot = chan0.value
# how much has it changed since the last read?
pot_adjust = abs(trim_pot - last_read)
if pot_adjust > tolerance:
trim_pot_changed = True
if trim_pot_changed:
# convert 16bit adc0 (0-65535) trim pot read into 0-100 volume level
set_volume = remap_range(trim_pot, 0, 65535, 0, 100)
# set OS volume playback volume
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)
# 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)
Let's put this file right in your home directory for simplicity. The wget command makes things easy.
$ wget https://raw.githubusercontent.com/adafruit/Adafruit_Learning_System_Guides/master/Analog_Inputs_for_Raspberry_Pi_Using_the_MCP3008/code.py
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