Potentiometer (ADC)

Lab 3: Potentiometer (ADC) — อ่านค่า Analog

วัตถุประสงค์

• Analog Input: อ่านค่าแบบ Analog (ไม่ใช่แค่ 0/1)

• ADC: เข้าใจหลักการแปลง Analog → Digital

• Scaling: แปลงค่า ADC เป็นหน่วยที่เข้าใจได้

จะได้เรียนรู้อะไร

• ADC Concept: 12-bit resolution (0-4095)

• Unit Conversion: ADC counts → millivolts → percentage

• Periodic Reading: อ่านค่าเป็นช่วงเวลา

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หลักการ ADC

   Analog Input        ┌─────────┐        Digital Output         
   (0 - 1.8V)    ────► │   ADC   │ ────►  (0 - 4095)             
                       └─────────┘        12-bit      

Analog Input (0V - 1.8V)     ADC     Digital Output (0 - 4095)
         │                    │              │
    1.8V ├────────────────────┼─────────────→ 4095
    0.9V ├────────────────────┼─────────────→ 2048
    0.0V ├────────────────────┼─────────────→ 0

Resolution 12-bit: 2^12 = 4096 ระดับ

สูตรแปลงเป็น mV:

$$mV = \frac{ADC\_count \times VREF\_mV}{4096}$$

Hardware Info

Component	Pin	หมายเหตุ
Potentiometer (POT)	P15_1	0-1800mV range
ADC Reference	Internal	1.8V

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Lab 3.1 : เพิ่ม ADC Macros และ Variables

/* ADC Configuration */
#define SAR_ADC_INDEX           (0U)
#define SAR_ADC_SEQUENCER       (0U)
#define SAR_ADC_CHANNEL         (0U)
#define SAR_ADC_VREF_MV         (1800U)
#define ADC_READ_INTERVAL_MS    (100U)

/* Global variables */
static bool adc_initialized = false;

สร้างฟังก์ชัน init_adc()

/*******************************************************************************
* Function Name: init_adc
********************************************************************************
* Summary:
*   Initialize the ADC for reading potentiometer
*
* Return:
*   cy_rslt_t - CY_RSLT_SUCCESS if successful
*******************************************************************************/
cy_rslt_t init_adc(void)
{
    cy_rslt_t result;

    /* Initialize SAR ADC */
    result = Cy_AutAnalog_Init(&autonomous_analog_init);

    if (CY_AUTANALOG_SUCCESS == result)
    {
        /* Set interrupt mask */
        Cy_AutAnalog_SetInterruptMask(CY_AUTANALOG_INT_SAR0_RESULT);

        /* Start autonomous control */
        Cy_AutAnalog_StartAutonomousControl();

        adc_initialized = true;
        printf("ADC initialized successfully\r\n");
    }
    else
    {
        printf("ADC initialization failed!\r\n");
    }

    return result;
}

สร้างฟังก์ชัน read_potentiometer_mv()

/*******************************************************************************
* Function Name: read_potentiometer_mv
********************************************************************************
* Summary:
*   Read potentiometer value and convert to millivolts
*
* Return:
*   int16_t - Voltage in millivolts (0-1800 mV), -1 if error
*******************************************************************************/
int16_t read_potentiometer_mv(void)
{
    if (!adc_initialized)
    {
        return -1;
    }

    /* Read ADC result (raw counts) */
    int32_t adc_count = Cy_AutAnalog_SAR_ReadResult(
        SAR_ADC_INDEX,
        CY_AUTANALOG_SAR_INPUT_GPIO,
        SAR_ADC_CHANNEL
    );

    /* Convert to millivolts */
    int16_t adc_mv = Cy_AutAnalog_SAR_CountsTo_mVolts(
        SAR_ADC_INDEX,
        false,
        SAR_ADC_SEQUENCER,
        CY_AUTANALOG_SAR_INPUT_GPIO,
        SAR_ADC_CHANNEL,
        SAR_ADC_VREF_MV,
        adc_count
    );

    return adc_mv;
}

สร้างฟังก์ชัน get_pot_percentage()

/*******************************************************************************
* Function Name: get_pot_percentage
********************************************************************************
* Summary:
*   Convert potentiometer voltage to percentage (0-100%)
*
* Return:
*   uint8_t - Percentage (0-100)
*******************************************************************************/
uint8_t get_pot_percentage(void)
{
    int16_t mv = read_potentiometer_mv();

    if (mv < 0) return 0;

    /* Map 0-1800 mV to 0-100% */
    uint8_t percentage = (uint8_t)((mv * 100) / SAR_ADC_VREF_MV);

    /* Clamp to 100% max */
    if (percentage > 100) percentage = 100;

    return percentage;
}

แก้ไข main()

int main(void)
{
    cy_rslt_t result = CY_RSLT_SUCCESS;
    uint32_t last_adc_read = 0;

    /* Initialize */
    result = cybsp_init();
    if (CY_RSLT_SUCCESS != result) { handle_app_error(); }

    __enable_irq();
    init_retarget_io();

    printf("\x1b[2J\x1b[;H");
    printf("*** PSoC Edge: ADC Demo ***\r\n\n");

    /* Initialize ADC */
    result = init_adc();
    if (CY_RSLT_SUCCESS != result)
    {
        printf("Warning: ADC init failed\r\n");
    }

    Cy_SysEnableCM55(MXCM55, CM55_APP_BOOT_ADDR, CM55_BOOT_WAIT_TIME_USEC);

    printf("Turn the potentiometer (POT) on the board.\r\n\n");

    /* Main loop */
    for(;;)
    {
        uint32_t current_time = Cy_SysLib_GetTimerTick();

        /* Read ADC every 100ms */
        if ((current_time - last_adc_read) >= ADC_READ_INTERVAL_MS)
        {
            last_adc_read = current_time;

            int16_t pot_mv = read_potentiometer_mv();
            uint8_t pot_pct = get_pot_percentage();

            printf("\rPOT: %4d mV (%3d%%)   ", pot_mv, pot_pct);
        }

        Cy_SysLib_Delay(10);
    }
}

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✍️ Exercise

1. LED Brightness Indicator : ใช้ POT ควบคุมจำนวน LED ที่ติด (ถ้ามี 4 LEDs)

• 0-25%: LED 1

• 25-50%: LED 1-2

• 50-75%: LED 1-3

• 75-100%: LED 1-4

1. Threshold Alert : แจ้งเตือนเมื่อ POT เกิน threshold ที่กำหนด

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