1. AUTOMATIC VOLUME CONTROL Team 37 Marius Berner and Muhammed Azam TA: Justine Fortier ECE 445: Senior Design Project December 4, 2013

2. INTRODUCTION Purpose of the project: to create a small sound system capable of adjusting the volume of a remote controlled device (i.e. a TV or stereo) based on what its current volume is in comparison to the background noise in the room Project ideally would eliminate need to toggle volume manually (via operation of a remote) for fluctuations of background noise in an environment (such as dogs barking, someone vacuuming, etc).

3. FEATURES Electret microphone with breakout board to detect and measure the background noise levels Noise cancellation circuitry to correct the microphone measurements for the TV contribution Arduino Uno R3 microcontroller coded to compare TV sound level to the rest of the room and control infrared transmissions based on the differential IR LED to transmit volume control signals User controllable audio thresholds via USB connections Transmits remote signals when device is placed from a 4 ft. distance from the television with detection capability of approximately 0.5 ft. from the televisions IR receiver Currently compatible with four major remote code protocols (NEC, Sony, RC5, RC6)

4. Phase Inverting Circuit Noise Limiter and Comparator Microcontroller Processing Unit Power Signal Noise Signal Volume Control Signal Tv Noise Signal mic Background + TV noise Remote Transmission Circuit Automatic Volume Control Block Diagram Speaker + 9V

5. Changes from original design Original plan: design an exponential circuit to correct the microphone signal for the noise of the TV before comparison of the two Problem: too unreliable and prone to delay Alternate plan: use active noise cancellation to cancel the noise of the TV at the microphone

6. Phase Inverting Noise Cancellation Circuit Purpose: to phase invert an AC voltage signal as well as eliminate any dc offset in the output Parts used: 1 - 20kohm resistor, 1- 4700uF capacitor, 1- LM 386N-1 (20 x gain) audio amplifier, and 1- 9V battery for the amplifier. Functionality: the signal goes through the 20 kOhm and the 4700uF capacitor works as an high pass filter. Its output is then send to the LM 386N-1 to be inverted.

7. Phase Inverter Circuit

8. High Pass Filter Verification Top green plot corresponds to the output after the high pass filter Bottom yellow plot corresponds to the input leading to the high pass filter Input on the function generator was.200Vpp with a 1Vdc offset.

9. Phase Inverter Verification

10. Noise Cancellation Plan was to use a speaker powered by 9V battery to output the inverted signal Speaker output would be added with the background noise (also containing TV noise) at the electret microphone to cancel out the TV noise from the background

11. Electret Microphone for Noise Detection Adafruit electret microphone with built in breakout board for amplification ($4.95) Outputs voltage signal of the audio level measurement

12. Requirement: must be able to detect sound levels and output the corresponding audio voltage signals Verification procedure: connect output voltage of the microphone to a voltage probe and display signal; create various noises and check that the microphone responds accordingly (Test results here are for 5 ft from the microphone and averaged over 5 trials per test case with 10 seconds per trial) Test SoundMax Voltage (V) Min Voltage (V) Quiet room (a lightly filled senior design lab) 1.200.60 Hammer (about half strength) 4.811.97 Clapping (half strength) 4.161.89 TV (40% max) 1.700.95 TV(80% max) 2.451.55

13. Comparator Purpose: to compare the TV noise signal with the background noise signal Parts used: 1 – 500 ohm resistor, 1- 9V battery, 1- 47 kOhm resistor, and 1- 24 kOhm resistor, 1- LM 386N-1

14. Comparator Circuit Diagram

15. Comparator Output Range Works best if inputs are in DC form and supply is 9 V. low (~ 700mVdc) when TV (- input) >background(+ input) mid (~3Vdc) when TV ~= background high (> ~ 4.76Vdc) when TV < background

16. Comparator Verification Procedure 0Vpp with a 0Vdc bias on negative input while grounding positive input Check output with oscilloscope and record value 0Vpp with a.1Vdc bias … Check output with oscilloscope and record value 0Vpp with a -.1Vdc bias … Check output with oscilloscope and record value

17. Remote Signal Transmission Remote signals transmitted via a 940nm wavelenghth infrared transmitter LED ($0.95) Microcontroller controls when to transmit the signals Smartphone camera can be used to determine whether the LED is emitting (since IR signals are typically non-visible to naked eye)

18. Requirement: correctly transmit remote code protocols for device (Sony TV) Using the public Arduino IRremote library (https://github.com/shirriff/Arduino-), infrared remote signals were obtained for various televisions using the IRrecvDump sketch and connecting a 38 kHz, 3-pin IR receiver to the Arduino.https://github.com/shirriff/Arduino- Most of the testing for the remote signal transmissions were done on the Sony TV we used for our demo (which uses Sony remote protocol) and an LG TV (which transmits NEC protocol signals) Button codes sent to receiver via Comcast universal remote

19. Remote ProtocolButtonDecoded IR code (in HEX) Number of bits SonyPOWER0xA9012 NECPOWER0x20DF40EF32 SonyVOLUME UP0x49012 NECVOLUME UP0x20DF40BF32 SonyVOLUME DOWN0xC9012 NECVOLUME DOWN0x20DFC03F32

20. Once IR signals for necessary buttons were decoded, IR LED was hooked up to Arduino Tested transmission by using various conditionals to command an IRsend function of the desired button from the transmitter: #include IRsend irsend; Through trial and error it was determined that the transmitter was able to send code from about 4 ft. from the TV and could be placed about 0.5 ft. to the left or right of the TV IR receiver at that distance

21. Sound Level Processing Unit The output of the comparison circuit is inputted into an Arduino Uno R3 microcontroller ($29.61) Used to control the IR transmitter LED Coded to send the appropriate remote button signals based on various voltage thresholds Power requirements: any battery that can source 7-12 V and over 500 mA of current (USB power can also be used)

22. Algorithm for Arduino code: Receives input from differential comparison circuit output (4.76 V for microphone > TV, 3.0 for approximate equality, and 0.7 V for microphone < TV) into analog input pin Scales voltages and computes a running average based on the squares of the inputs (to avoid opposite signed sound signals from negating each other before taking the average sound level) Creates constant voltage thresholds based on the comparison circuit to compare the inputs to: 1. If running average > 4.20-V, send volume up signal 2. If 2.85-V<running average < 4.20-V, do nothing 3. Otherwise send volume down signal

23. Requirements: command the IR LED to transmit distinct remote signals based on the voltage received as analog input Once the code was written testing was fairly straightforward: simply modify the voltage thresholds in the code and checked to ensure that the volume signals were or werent being sent accordingly Problem 1: originally code saw issues due to the large nature of the running average of squared values (i.e. the analog pin was reading significantly different values for voltage values very close to each other, making it difficult to set thresholds Solution: subtract an central offset (2.5-V) from each sample before squaring This temporarily caused an issue of negative values being introduced to the microcontroller for V < 2.5-V, which it processed as looping back around and caused certain low signals to be read as high Solution: change to a variable offset

24. Problems/Future Improvements Comparator cannot take in AC inputs (output seem to be the sum of both inputs) so AC inputs should be converted to DC. Although we used a battery, a constant power supply of 7V is needed for the output of the comparator circuit. TV noise input and Speaker couldnt be fully implemented in our circuit Solution might be to use a mono audio jack rather than a stereo audio jack (for our TV) Design not fully transferred to a PCB/vector board

25. Acknowledgements Professor Makela Justine Fortier 445 TAs/course staff Parts Shop Personnel