Python script for Raspberry Pi, Adafruit 7-segment 4-digit LCD backpack and a LED. Uses an USB mic to measure and display sound level.

SoundMonitor.py

#!/usr/bin/python

# Sound level indicator on a 7-segment 4-digit LCD, for Raspberry Pi
# Uses a USB mic to measure sound level
# 
# https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code/blob/master/Adafruit_LEDBackpack/Adafruit_7Segment.py
# https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code/blob/master/Adafruit_LEDBackpack/Adafruit_LEDBackpack.py
# https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code/blob/master/Adafruit_I2C/Adafruit_I2C.py
# 
# Author Ando Roots <ando@sqroot.eu> 2013
# http://sqroot.eu

import alsaaudio, time, audioop, datetime
from Adafruit_7Segment import SevenSegment
import RPi.GPIO as GPIO

class SoundMonitor:
  
	# Red LED address
	RED_LED = 23
	
	# Light red LED when measured sound value exceeds the preset limit
	WARNING_THRESHOLD = 800
	
	# Tolerance as a percentage (0.5 is 50%)
	# LCD output is changed when the measured value exceeds this tolerance
	TOLERANCE = 0.15
	
	# Minimum time in seconds between each LCD value change
	MAX_CHANGE_FREQ = 0.5	
	
	# 7-segment display (run i2cdetect -y 1 to get the addr)
	segment = SevenSegment(address=0x70)
	
	# Alsaaudio instance
	inp = alsaaudio.PCM(alsaaudio.PCM_CAPTURE,alsaaudio.PCM_NORMAL, 'sysdefault:CARD=Set')
	
	def __init__(self):
		
		# LED
		GPIO.setmode(GPIO.BCM)
		GPIO.setup(self.RED_LED, GPIO.OUT)
		
		# Set attributes: Mono, 8000 Hz, 16 bit little endian samples
		self.inp.setchannels(1)
		self.inp.setrate(8000)
		self.inp.setformat(alsaaudio.PCM_FORMAT_S16_LE)
		self.inp.setperiodsize(160)

	
	# Write a 4-digit number to the LCD
	def write_number(self, value):
		value = int(value)
		if value > 9999:
			print "Value %s is out of bounds, setting to 9999" % value
			value = 9999
		value = str(value).zfill(4)
		self.segment.writeDigit(0, int(value[0]))
		self.segment.writeDigit(1, int(value[1]))
		self.segment.writeDigit(3, int(value[2]))
		self.segment.writeDigit(4, int(value[3]))
		return self
	
	# Get the current sound level
	def get_sound_level(self):
		
		# Read data from device
		l,data = self.inp.read()
		if not l:
			return 1
		
		# Return the maximum of the absolute value of all samples in a fragment.
		value = float(audioop.max(data, 2))
		if value < 1:
			value = 1.0
		return value
	
	# Main loop
	def run(self):
		print "Running the program - press Ctrl + C to exit."
		time.sleep(2)
		
		saved_value = 1
		last_changed = time.time()
		
		while True:
			value = self.get_sound_level()
			red_state = value > self.WARNING_THRESHOLD 
			
			print "Level: %s; Red: %s;" % (value, red_state)
			if abs((saved_value - value) / value) > self.TOLERANCE:
				if time.time() > last_changed + self.MAX_CHANGE_FREQ:
					self.write_number(value) # Change LCD output
					GPIO.output(self.RED_LED, red_state) # Light red LED?
					saved_value = value
					last_changed = time.time()
		
		time.sleep(.001)
		    
    # Cleanup on exit
	def __del__(self):
		self.segment.disp.clear()
		GPIO.cleanup()
		
# Run the program
monitor = SoundMonitor().run()