Project

# Build an Audio Detector

August 09, 2015 by Travis Fagerness

## Detect audio with an electret microphone and a TI CC3200 Wifi microcontroller. This handy project will allow you to set up an audio detection device that can be used to catch your roommate stealing things from the fridge or send you an alert if the noise in your room goes above a certain threshold.

Detect audio with an electret microphone and a TI CC3200 Wifi microcontroller.

Intermediate

### Requirements

• CC3200 Demo board
• Updated to latest firmware for Energia support, directions here.
• Energia - Arduino IDE Clone from TI
• Use in article: v. 0101E00016
• Electret Microphone
• Used in article: BOB-09964
• *This board requires modification to work with CC3200
• Jumper wires
• Device capable of running Python with a UDP server

### Hardware Setup

#### Modifying the microphone

Unfortunately the CC3200 can only read voltages up to 1.45V on the ADC pins. Since we'll be powering the microphone from 3.3V, we need to modify the circuit to output a voltage of 1.45/2 = 0.725V when no sound is present. Resistors R2 and R3 in the schematic for a voltage divider that sets the bias point. To change it to 0.725V, we can calculate a new resistor based on the common voltage divider equation. This works out to changing the resistor R3 to 2.82k. The closest 1% value is 2.8k, and the closest 5% value is 3k. I would recommend using a 2.8k resistor if you can find one. The value isn't extremely critical if you don't have many resistors lying around, you just may introduce distortion in the signal if the bias is too far low or high in voltage.

#### Connecting the wires

CC3200 pinout here.

CC3200  BOB-09964
Pin 1 -- 3v3 Power  VCC
Pin 22 -- GND  GND

#### Testing the connection

The code below implements sampling the input from the microphone. It calculates a moving average of the RMS value from the microphone. It then prints a bar graph to the serial terminal indicating how much audio energy there is.

2. Open the sketch in Energia.
1. File>Open>audio_RMS_print.ino
2. Make sure to select the correct board in Tools>Board>Launchpad w/ CC3200 80MHz.
3. Program the board.
1. File>Upload or the arrow button
4. You should see the bar graph in a terminal move depending on the audio. *Note: The built-in terminal doesn't handle the '/r' to display the graph. I recommend Tera Term instead.

audio_RMS_print.zip

### Transmitting over WiFi

The following code adds WiFi capability to the audio detector.

2. Open the sketch in Energia.
1. File>Open>audio_RMS_print.ino
2. Make sure to select the correct board in Tools>Board>Launchpad w/ CC3200 80MHz.
3. Modify the network constants below
4. Program the board.
5. File>Upload or the arrow button.
6. The CC3200 will now transmit over UDP every time a new average is measured.

/*network settings*/
char ssid[] = "yourSSID";                     //SSID of network
char UDP_server_IP[] = "yourserverpassword";  //IP address of UDP server to send data to
int UDP_server_port = 9999;



audio_detector.zip

### Setting up a Python UDP Server

The following code starts a UDP server at the specified IP address and port. It expects two bytes sent with every UDP packet. It converts the two bytes to an int16 number and converts it to a bar graph displayed on the console. Executing this script while the CC3200 is running the code above will display a bar graph when audio is playing near the microphone.


import SocketServer
import struct
import sys

class MyUDPHandler(SocketServer.BaseRequestHandler):
def handle(self):
data = self.request[0].strip()
socket = self.request[1]
try:
moving_average = struct.unpack('h',data)[0]
bar_chart = moving_average
print "\r                         \r",
while bar_chart > 0:
sys.stdout.write('#')
bar_chart = bar_chart - 200
except:
pass

if __name__ == "__main__":
server = SocketServer.UDPServer((HOST, PORT), MyUDPHandler)
server.serve_forever()



Room.zip

1. Make sure you have a Gmail account that allows "Less secure apps" to communicate.
2. Adjust the "EMAIL_THRESHOLD" to the audio energy you want to send an email at.
4. Execute the script. You should see the following when the threshold is reached. If you want to keep sending emails forever, remove the variable "already_sent_once".
5. Email in the inbox:

import SocketServer
import struct
import sys
import smtplib
from email.mime.text import MIMEText

HOST, PORT = "yourip", 9999
EMAIL_THRESHOLD = 600
moving_average = 0
class MyUDPHandler(SocketServer.BaseRequestHandler):
def handle(self):
data = self.request[0].strip()
socket = self.request[1]
try:
moving_average = struct.unpack('h',data)[0]
bar_chart = moving_average
print "\r                         \r",
while bar_chart > 0:
sys.stdout.write('#')
bar_chart = bar_chart - 200
except:
pass
if moving_average > EMAIL_THRESHOLD and already_sent_once == 0:
print "Sending email, audio above threshold: " + str(moving_average)
msg = MIMEText("Audio is at level: " + str(moving_average))
msg['Subject'] = 'Audio above threshold'
s = smtplib.SMTP('smtp.gmail.com:587')
s.ehlo()
s.starttls()
s.quit()

if __name__ == "__main__":
server = SocketServer.UDPServer((HOST, PORT), MyUDPHandler)
server.serve_forever()



room2.zip

#### Video

Give this project a try for yourself! Get the BOM.

• M
mafiaWolf August 12, 2015

Dont you have any audio streaming demo? Stream audio from PC to CC3200 launchxl (within AudioBoosterpack etc.) Thanks for your attention

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• Paul Flanagan November 23, 2015

Hi. I’m new to the hardware side of things. Can you explain how you added the resistor or resistors to the Electret Microphone? Have you any pictures or resources I could follow? I’m trying to get this example up and running. Any help would be greatly appreciated. Thanks

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• P
phuangcn March 11, 2016

Hi Travis, it seems like there is no 2.8k resistor between P23 and Mic on your diagram. Could you double check it?

By the way, if I use this MEMS Mic (https://www.sparkfun.com/products/9868), should I still use 2.8K resistor to lower the voltage?

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