Noise Generator

Lab 2: Noise Generator

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1. โครงสร้างภาพรวมของ Lab

Why? - ทำไมต้องเรียนรู้เรื่องนี้

• Testing: ใช้ noise สำหรับทดสอบ filter และ signal processing

• Random Data: เข้าใจการสร้างข้อมูลสุ่ม

• RMS Calculation: วัดค่า RMS ของ noise

What? - จะได้เรียนรู้อะไร

1. Noise Generation: aic_scope_generate_noise()

2. Timer-based Update: อัพเดท noise แบบต่อเนื่อง

3. RMS Measurement: aic_scope_calc_rms()

4. Start/Stop Control: ควบคุมการ generate

How? - จะทำอย่างไร

1. สร้าง Chart แสดง noise

2. ใช้ Timer อัพเดทข้อมูลทุก 100ms

3. แสดงค่า RMS แบบ real-time

4. เพิ่มปุ่ม Start/Stop

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2. หลักการทำงานและ Flowchart

2.1 White Noise Characteristics

┌─────────────────────────────────────────────────────────────┐
│                    WHITE NOISE                              │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│   Time Domain:                                              │
│                                                             │
│   ▃▅█▂▇▃▆▁▄█▅▂▇▃▅▁▄▇▂▃█▅▆▁▄▅▃▇▂█▄▅▃▆▁▇▂▅▃█▄▆▁               │
│                                                             │
│   - Random amplitude at each sample                         │
│   - No pattern or periodicity                               │
│   - Contains all frequencies equally                        │
│                                                             │
│   Frequency Domain:                                         │
│                                                             │
│   ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓  ← Flat spectrum         │
│   ─────────────────────────────────                         │
│   0 Hz                          Fs/2                        │
│                                                             │
└─────────────────────────────────────────────────────────────┘

2.2 RMS Calculation

┌─────────────────────────────────────────────────────────────┐
│                  RMS (Root Mean Square)                     │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│   Formula:                                                  │
│                                                             │
│         ┌─────────────────────────────┐                     │
│         │    1   N-1                  │                     │
│   RMS = │   ─── Σ  x[i]²              │                     │
│         │    N  i=0                   │                     │
│         └─────────────────────────────┘                     │
│                                                             │
│   Example:                                                  │
│   Samples: [100, -50, 75, -100, 50]                         │
│   Squares: [10000, 2500, 5625, 10000, 2500]                 │
│   Mean: 30625 / 5 = 6125                                    │
│   RMS: sqrt(6125) = 78.3                                    │
│                                                             │
│   For noise with amplitude ±1000:                           │
│   Theoretical RMS ≈ 1000 / √3 ≈ 577                         │
│                                                             │
└─────────────────────────────────────────────────────────────┘

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3. ฟังก์ชันสำคัญ

3.1 Noise Generation

void aic_scope_generate_noise(int16_t *buffer, uint16_t count, int16_t amplitude);

Parameter	Description
buffer	Output array
count	Number of samples
amplitude	Max amplitude (±amplitude)

3.2 RMS Calculation

float aic_scope_calc_rms(const int16_t *buffer, uint16_t count);

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4. Code Example

4.1 Global Variables

#define BUFFER_SIZE     256

static int16_t noise_buffer[BUFFER_SIZE];
static lv_obj_t *noise_chart = NULL;
static lv_chart_series_t *noise_series = NULL;
static lv_obj_t *rms_label = NULL;
static lv_obj_t *btn_label = NULL;
static lv_timer_t *noise_timer = NULL;
static bool noise_running = false;

4.2 Timer Callback

static void noise_timer_cb(lv_timer_t *timer)
{
    (void)timer;

    if (!noise_running) return;

    /* Generate new random noise */
    aic_scope_generate_noise(noise_buffer, BUFFER_SIZE, 1000);

    /* Update Chart */
    for (int i = 0; i < 200; i++) {
        int32_t val = (noise_buffer[i] + 1000) / 20;
        lv_chart_set_value_by_id(noise_chart, noise_series, i, val);
    }
    lv_chart_refresh(noise_chart);

    /* Update RMS */
    float rms = aic_scope_calc_rms(noise_buffer, BUFFER_SIZE);
    lv_label_set_text_fmt(rms_label, "RMS: %.1f", (double)rms);
}

4.3 Button Callback

static void start_stop_btn_cb(lv_event_t *e)
{
    (void)e;
    noise_running = !noise_running;
    lv_label_set_text(btn_label, noise_running ? "Stop" : "Start");
}

4.4 Main Function

void week5_ex2_noise_generator(void)
{
    lv_obj_t *scr = lv_screen_active();

    /* Title */
    lv_obj_t *title = lv_label_create(scr);
    lv_label_set_text(title, "Week 5 Ex2: Noise Generator");
    lv_obj_align(title, LV_ALIGN_TOP_MID, 0, 5);

    /* Chart */
    noise_chart = lv_chart_create(scr);
    lv_obj_set_size(noise_chart, 350, 150);
    lv_obj_align(noise_chart, LV_ALIGN_TOP_MID, 0, 35);
    lv_chart_set_type(noise_chart, LV_CHART_TYPE_LINE);
    lv_chart_set_point_count(noise_chart, 200);
    lv_chart_set_range(noise_chart, LV_CHART_AXIS_PRIMARY_Y, 0, 100);
    lv_obj_set_style_size(noise_chart, 0, 0, LV_PART_INDICATOR);

    noise_series = lv_chart_add_series(noise_chart,
                       lv_color_hex(0xff6600),
                       LV_CHART_AXIS_PRIMARY_Y);

    /* Start/Stop Button */
    lv_obj_t *btn = lv_btn_create(scr);
    lv_obj_set_size(btn, 100, 40);
    lv_obj_align(btn, LV_ALIGN_CENTER, 0, 30);
    lv_obj_add_event_cb(btn, start_stop_btn_cb, LV_EVENT_CLICKED, NULL);

    btn_label = lv_label_create(btn);
    lv_label_set_text(btn_label, "Start");
    lv_obj_center(btn_label);

    /* RMS Label */
    rms_label = lv_label_create(scr);
    lv_label_set_text(rms_label, "RMS: 0.0");
    lv_obj_set_style_text_font(rms_label, &lv_font_montserrat_24, 0);
    lv_obj_align(rms_label, LV_ALIGN_BOTTOM_MID, 0, -30);

    /* Timer */
    noise_timer = lv_timer_create(noise_timer_cb, 100, NULL);
}

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5. องค์ความรู้และเทคนิค

5.1 Pseudo-Random Number Generation

/* Simple Linear Congruential Generator */
static uint32_t seed = 12345;

int16_t random_sample(int16_t amplitude)
{
    seed = seed * 1103515245 + 12345;
    int32_t val = (seed >> 16) & 0x7FFF;  /* 0 to 32767 */
    val = val - 16384;                     /* -16384 to +16383 */
    val = (val * amplitude) / 16384;       /* Scale to amplitude */
    return (int16_t)val;
}

5.2 Timer vs Manual Update

/* Timer-based: Automatic continuous update */
lv_timer_create(noise_timer_cb, 100, NULL);  /* Every 100ms */

/* Manual: Update on button press only */
void btn_cb(lv_event_t *e) {
    generate_and_display();
}

5.3 Start/Stop Pattern

/* Common pattern for real-time displays */
static bool running = false;

void timer_cb(lv_timer_t *t) {
    if (!running) return;  /* Early exit if stopped */
    /* ... update logic ... */
}

void toggle_cb(lv_event_t *e) {
    running = !running;
    lv_label_set_text(label, running ? "Stop" : "Start");
}

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6. แบบฝึกหัด

Exercise 1: Peak-to-Peak Display

เพิ่มการแสดงค่า Peak-to-Peak ของ noise

Exercise 2: Amplitude Control

เพิ่ม Slider ปรับ amplitude ของ noise (100-2000)

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7. References

• White Noise

• RMS Calculation

• LVGL Button

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