SIS project n 1: Sound detection with a real e-puck. David FitzGerald Daniel Kroiss

Transcription

1 SIS project n 1:

2 Goal: Program an e-puck in order to find a sound source. Equipment: Two e-pucks Three batteries Bluetooth USB key Programming language: C 2

3 Procedure: 1. Record the sound 2. Apply the Fast Fourier Transform 3. Calculate the phase and phase differences 4. Determine the sinus of the angle between the e-puck orientation and the sound direction 5. Clean the values and do a normalisation 6. Calculate the angle between the e-puck orientation and the sound direction 7. Set the wheel speeds 3

4 1. Sound recording: The sound is sampled with three microphones and stored in an array: // 1. Get Sound e_ad_scan_on(); while(!e_ad_is_array_filled()); e_ad_scan_off(); 2. Fast Fourier Transform The fast fourier transform is calculated by the following function: // i. Substract mean of vector e_subtract_mean(e_mic_scan[k], FFT_BLOCK_LENGTH, LOG2_BLOCK_LENGTH); // ii. Copy vector into sigcmpx e_fast_copy(e_mic_scan[k], (int*)sigcmpx, FFT_BLOCK_LENGTH); // iii. Do FFT. The result is stored in sigcmpx. e_dofft_asm(sigcmpx); 4

5 3. Phase: The phase is determined using the following line of code: // iv. Phase calculation theta[k] = atan2(sigcmpx[ind_fft].imag, sigcmpx[ind_fft].real); It requires the index (IND_FFT) thats corresponds to the sound frequency (880 Hz). We can find it by plotting the magnitude of the signal. We chose the index 22, for which the frequency is: 22 33'000 f Hz 256/ 2 2 (33'000 Hz microphone sampling frequency) 5

6 3. Phase difference: The phase difference is related to the time it takes the sound to go from one microphone to another: Δt = Δϕ 2 π f For example: Δ ϕ10 = ϕ0 ϕ1 At this point it is possible to use Δφ to make the e-puck turn towards the sound source. 6

7 3. Phase difference: Forward direction Δ ϕ10 = ϕ0 ϕ1 Δφ10 > 0 Δφ10 < 0 If Δφ10 > 0: turn left Mic 1 Mic 0 If Δφ10 < 0: turn right Else: go forward or turn around (depending on the sign of Δφ20 and Δφ21) Mic 2 Works well 7

8 4. Sinus determination: The angle is given by: v Δ t θ = arcsin x ( ) where v is the speed of sound. 8

9 5. Sinus filtering: a= v Δ t x must have a value between -1 and 1 Normalization required Plot of a values and cleaned a values 9

10 5. Sinus filtering implementation: // iv. Normalisation for (k=0;k<3;k++) { // Clean amplified values if (a[k] > 1) { a[k] = -0.5; } else if (a[k] < -1) { a[k] = 0.5; } // Normalisation if (a[k] > 0) { a[k] = a[k]/max_value[k]; } else { a[k] = -a[k]/min_value[k]; } // Clean max and min values if (a[k] > 1) { a[k] = 1; } else if (a[k] < -1) { a[k] = -1; } } 10

11 6. Angle θ: One angle is not sufficient to determine the direction of the sound. We computed the angle θ21 for mic2 & mic1, and θ20 for mic2 & mic0? Mic 0 Mic 1 θ20 & θ21 real θ Mic 2 θ20 = θ20 11

12 6. Angle β: We defined the angle β (comprised between -π and π) based on θ21 and θ20. Forward direction β>0 Result when making the sound source turn around the e-puck: β<0 12

13 7. Wheel speed: Forward direction e_set_speed_ e_set_speed_ right left I II III a III b IV Stopping condition: if (e_get_prox(k) > sensitivity level ) { e_set_speed_left(0); e_set_speed_right(0); } I IV II a III b 13

14 Performance: The method using β works as well as the method that uses the sign of Δφ. The fluidity was improved by removing the NaN values of φ. The time needed to reach the sound source is directly dependent on the wheel speeds. Problems encountered: The IR sensors could cause the e-puck to stop randomly due to the lighting conditions. The maximum distance between the e-puck and the sound source up to which sound is detected is pretty small (~70 cm). Unreliable Bluetooth connection. 14

15 Possible improvements: The performance could be improved by better filtering the signal. The accuracy of β could be better with more correct values for the normalization (max_value and min_value). Use several consecutive samples before calculating the angle in order to reduce the influence of the noise. 15

16 Conclusion: What was important for us was the precision of the angle β. The time needed to reach the sound source was secondary. Through this project, we were able to see that the method using the FFT works pretty well. However, it would be interesting to compare it with other methods. //Thank you for your attention! 16

17 References: =2&Itemid=8 er-en-c /firmware/btcomdm.c 17