SirenDetect. Jennifer Michelstein Department of Electrical Engineering Adviser: Professor Peter Kindlmann May 1, 2003. Alerting Drivers about Emergency Vehicles. GPS. INSIDE A CAR. BUTTONS. CALENDAR/MINI PC. INSIDE A CAR. RADIO, CD PLAYER, SPEAKERS. PHONE WITH BUTTONS IN STEERING WHEEL.
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Department of Electrical Engineering
Adviser: Professor Peter Kindlmann
May 1, 2003
Alerting Drivers about Emergency Vehicles
INSIDE A CAR
INSIDE A CAR
RADIO, CD PLAYER, SPEAKERS
PHONE WITH BUTTONS IN STEERING WHEEL
Cars have too many distractions.
Added features = Less attention to the road and other vehicles.
Driving has become perilous.
SirenDetect Summary of Key Features
1) Software Solution
Matlab version 6.0 to analyze frequencyplots of sirens, construct filtering algorithms.
2) Hardware Solution
Motorola DSP56826evm Digital Signal Processing kit with Metrowerks CodeWarrier software to create the device.
The FFT is an algorithm that “reduces the number of computations from something on the order of N02 to N0 log N0.”*
Fast Fourier Transform (FFT)
FFT of Sample Siren
105 – 180 Hz
370 - 430 Hz
220 – 300 Hz
The Butterworth Filter
N - order of the filter; - analog frequency; s - complex Laplace variable such that s = + j.
* Kuc, Roman. Introduction to Digital Signal Processing. New York: McGraw-Hill, 1988.
Butterworth Filtering with Matlab
n - order of the filter
Wn - the two-element vector Wn = [f1, f2] where f1, f2 are the limits of the passband, scaled from 0 to 1
[b,a] - filtering coefficients
By experiment, n1 = n2 = 8; n3 = 6.
1. Create three bandpass Butterworth filters for P1, P2, P3.
2. Construct filters in parallel; pass siren through filters.
3. Obtain peak amplitude of each key region.
4. Repeat steps 2-3 for multiple siren samples; average
amplitudes to obtain typical A1, A2, A3.
5. Run current sound sample through parallel filters; compare
resulting amplitudes to A1, A2, and A3 to determine if sample
is a siren.
Filtering: Graphical Representation of Inputs
Filtering: Graphical Representation of Outputs
Bandpass Region 1
Bandpass Region 2
Bandpass Region 3
1. Absolute Magnitude Comparisons.
Advantages: Simple(st), Fast(est), and Inexpensive Implementation.
Disadvantages: Inaccuracy in presence of noise, disturbances.
Next: How to compare bandpass regions?
2. Respective Magnitude Comparisons.
Advantages: Simple, Fast, and Inexpensive; high accuracy.
Disadvantages: Robustness? Testing necessary.
How to compare bandpass regions? (continued)
3. Time Domain.
Advantages: High Accuracy.
Disadvantages: Difficult, more costly implementation.
4. Combination of 2 (Relative Magnitudes) and 3 (Time Domain).
Advantages: Greatest Accuracy.
Disadvantages: Costly and possibly redundant algorithm.
Testing various algorithms proved that comparing respective amplitudes was the ideal implementation. Adjusting thresholds after testing various siren samples made detection more reliable.
Matlab Code for Relative Amplitudes
if (x13 > ??) & (x13 < ??) true2 = 1;end;if (x23 > ??) & (x23 < ??) true3 = 1;end;if (true1) & (true2) & (true3) its_a_siren=1;end;
x12 = max1 / max2;x13 = max1 / max3;x23 = max2 / max3;true1 = 0;true2 = 0;true3 = 0;its_a_siren=0;if (x12 >??) & (x12 < ??) true1 = 1;end;
R1 = max(x1)/max(x2)
R2 = max(x1)/max(x3)
R3 = max(x2)/max(x3)
FFT Algorithm for
Flow Chart - Top Level
all incoming sound
Real Time Data Stream
Comparisons to R1, R2, R3
LED’s on / off
Repeat Process on Motorola DSP56826evm Digital Signal Processing kit with Metrowerks CodeWarrier.
Test in Laboratory Setting using microphones oriented in various directions; sirens mixed with street noises, music, etc.
1. Siren Library Expansion.
SirenDetect will store a fingerprint for each of the
unique siren sounds emitted by emergency vehicles.
The Future of SirenDetect
2. Siren Differentiation.
SirenDetect will distinguish between the siren of an
ambulance, fire truck, police car, or other emergency
vehicle. The driver will be notified of the type of car
that is approaching.
The Future of SirenDetect (continued)
3. Directional Capabilities.
Strategic positioning of microphones will allow
SirenDetect to compare amplitudes of signals and
identify the precise location from which the emergency
vehicle is approaching.
The Future of SirenDetect (continued)
4. Robustness Evaluation.
The system must be tested in residential areas, on highways,
in cars traveling the same direction as emergency vehicles, the
opposite direction, and at various angles (30, 45, 60, 90, etc.).
Possible hazards are the Doppler effect and noise interference.
The thresholds employed in the current code may need
slight adjustments to be comprehensive in various driving
conditions, yet should not be all-inclusive (i.e. detecting
too many noises as sirens). Efficiency - Accuracy Trade-Off.
Peter Kindlmann, Project Adviser