Merge pull request adafruit#515 from adafruit/Analog_Inputs_for_Raspberry_Pi_Using_the_MCP3008

Analog inputs for raspberry pi using the mcp3008

Author: ladyada

Analog_Inputs_for_Raspberry_Pi_Using_the_MCP3008/Analog_Inputs_for_Raspberry_Pi_Using_the_MCP3008-Pi-Cobbler.fzz

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+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)

Analog_Inputs_for_Raspberry_Pi_Using_the_MCP3008/Analog_Inputs_for_Raspberry_Pi_Using_the_MCP3008-T-Cobbler-Plus.fzz

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+# Analog_Inputs_for_Raspberry_Pi_Using_the_MCP3008
+
+Code to accompany this tutorial:
+https://learn.adafruit.com/reading-a-analog-in-and-controlling-audio-volume-with-the-raspberry-pi