# 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
***
### 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 |
***
### Lab 3.1 : แก้ไข Macros เดิมจาก
```c
/*******************************************************************************
* Macros
******************************************************************************/
#define CM55_BOOT_WAIT_TIME_USEC (10U)
#define ADC_SCAN_DELAY_MSEC (500U) <-- เดิม
#define SAR_ADC_INDEX (0U)
#define SAR_ADC_SEQENCER (0U) <-- เดิม
#define SAR_ADC_CHANNEL (0U)
#define SAR_ADC_VREF_MV (1800U)
```
#### เป็น Macros ใหม่ , เพิ่ม Variables และ ชื่อฟังก์ชันเพิ่มเติม ดังนี้
```c
/*******************************************************************************
* Macros
******************************************************************************/
#define CM55_BOOT_WAIT_TIME_USEC (10U)
#define ADC_READ_INTERVAL_MS (100U)
#define SAR_ADC_INDEX (0U)
#define SAR_ADC_SEQUENCER (0U)
#define SAR_ADC_CHANNEL (0U)
#define SAR_ADC_VREF_MV (1800U)
/*******************************************************************************
* Global Variables
*******************************************************************************/
static bool adc_initialized = false;
/*******************************************************************************
* Function Prototypes
*******************************************************************************/
static cy_rslt_t init_adc(void);
static int16_t read_potentiometer_mv(void);
static uint8_t get_pot_percentage(int16_t voltage_mv);
```
#### สร้างฟังก์ชัน init\_adc()
```c
/*******************************************************************************
* Function Name: init_adc
********************************************************************************
* Summary:
* Initializes the SAR ADC using autonomous analog control.
* Sets up interrupt masks and enables autonomous operation.
*
* Parameters:
* none
*
* Return:
* cy_rslt_t - CY_RSLT_SUCCESS if initialization successful
*
*******************************************************************************/
static cy_rslt_t init_adc(void)
{
cy_rslt_t result;
/* Initialize SAR ADC with autonomous analog configuration */
result = Cy_AutAnalog_Init(&autonomous_analog_init);
if (CY_AUTANALOG_SUCCESS != result)
{
return result;
}
/* Set interrupt mask to enable SAR0 result interrupt */
Cy_AutAnalog_SetInterruptMask(CY_AUTANALOG_INT_SAR0_RESULT);
/* Start autonomous control of the ADC */
Cy_AutAnalog_StartAutonomousControl();
adc_initialized = true;
return CY_RSLT_SUCCESS;
}
```
#### สร้างฟังก์ชัน read\_potentiometer\_mv()
```c
/*******************************************************************************
* Function Name: read_potentiometer_mv
********************************************************************************
* Summary:
* Reads the potentiometer value from ADC and converts to millivolts.
* Uses the autonomous analog SAR ADC API.
*
* Parameters:
* none
*
* Return:
* int16_t - Voltage in millivolts (0-1800 mV)
*
*******************************************************************************/
static int16_t read_potentiometer_mv(void)
{
int32_t adc_count;
int16_t voltage_mv;
/* Read ADC result (raw counts) */
adc_count = Cy_AutAnalog_SAR_ReadResult(SAR_ADC_INDEX,
CY_AUTANALOG_SAR_INPUT_GPIO,
SAR_ADC_CHANNEL);
/* Convert ADC counts to millivolts */
voltage_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 voltage_mv;
}
```
#### สร้างฟังก์ชัน get\_pot\_percentage()
```c
/*******************************************************************************
* Function Name: get_pot_percentage
********************************************************************************
* Summary:
* Converts potentiometer voltage to percentage (0-100%).
* Maps the voltage range (0 to VREF_MV) to percentage scale.
*
* Parameters:
* voltage_mv - Input voltage in millivolts
*
* Return:
* uint8_t - Percentage value (0-100)
*
*******************************************************************************/
static uint8_t get_pot_percentage(int16_t voltage_mv)
{
int32_t percentage;
/* Ensure voltage is within valid range */
if (voltage_mv < 0)
{
voltage_mv = 0;
}
else if (voltage_mv > SAR_ADC_VREF_MV)
{
voltage_mv = SAR_ADC_VREF_MV;
}
/* Calculate percentage: (voltage / VREF) * 100 */
percentage = ((int32_t)voltage_mv * 100) / SAR_ADC_VREF_MV;
return (uint8_t)percentage;
}
```
#### ปรับปรุง main() ใหม่
```c
int main(void)
{
cy_rslt_t result = CY_RSLT_SUCCESS;
int16_t voltage_mv;
uint8_t percentage;
/* Initialize the device and board peripherals. */
result = cybsp_init();
/* Board initialization failed. Stop program execution. */
if (CY_RSLT_SUCCESS != result)
{
handle_app_error();
}
/* Enable global interrupts */
__enable_irq();
/* Initialize retarget-io middleware */
init_retarget_io();
/* \x1b[2J\x1b[;H - ANSI ESC sequence for clear screen. */
printf("\x1b[2J\x1b[;H");
printf("***********************************************************\r\n");
printf(" PSOC Edge MCU: Potentiometer ADC \r\n");
printf("***********************************************************\r\n\n");
/* Initialize SAR ADC using helper function */
result = init_adc();
if (CY_RSLT_SUCCESS != result)
{
printf("ADC initialization failed!\r\n");
handle_app_error();
}
/* Inform user about potentiometer connection */
printf("ADC initialized successfully!\r\n");
printf("Reading potentiometer on pin P15_1\r\n");
printf("VREF = %d mV (12-bit resolution)\r\n\n", SAR_ADC_VREF_MV);
/* CY_CM55_APP_BOOT_ADDR must be updated if CM55 memory layout is changed.*/
Cy_SysEnableCM55(MXCM55, CY_CM55_APP_BOOT_ADDR, CM55_BOOT_WAIT_TIME_USEC);
for(;;)
{
/* Read potentiometer voltage using helper function */
voltage_mv = read_potentiometer_mv();
/* Convert to percentage using helper function */
percentage = get_pot_percentage(voltage_mv);
/* Print ADC output in millivolts and percentage */
printf("POT: %4d mV | %3d%%\r\n", voltage_mv, percentage);
/* Toggle user LED to indicate activity */
Cy_GPIO_Inv(CYBSP_USER_LED_PORT, CYBSP_USER_LED_PIN);
/* Delay between ADC readings */
Cy_SysLib_Delay(ADC_READ_INTERVAL_MS);
}
}
```
#### ตัวอย่าง Output บน Serial Terminal
```bash
***********************************************************
PSOC Edge MCU: Potentiometer ADC
***********************************************************
ADC initialized successfully!
Reading potentiometer on pin P15_1
VREF = 1800 mV (12-bit resolution)
POT: 0 mV | 0%
POT: 450 mV | 25%
POT: 900 mV | 50%
POT: 1350 mV | 75%
POT: 1800 mV | 100%
```
### ADC Potentiometer Flowcharts
#### Overall Program Flow and init\_adc() Flowchart
***
#### read\_potentiometer\_mv() Flowchart
```bash
┌─────────────────────────────────────────────────────────────────┐
│ read_potentiometer_mv() Function │
├─────────────────────────────────────────────────────────────────┤
│ │
│ ┌──────────────────┐ │
│ │ START │ │
│ └────────┬─────────┘ │
│ │ │
│ ▼ │
│ ┌──────────────────────────────────────┐ │
│ │ adc_count = Cy_AutAnalog_SAR_ │ │
│ │ ReadResult( │ │
│ │ SAR_ADC_INDEX, │ │
│ │ CY_AUTANALOG_SAR_INPUT_GPIO, │ │
│ │ SAR_ADC_CHANNEL │ │
│ │ ) │ │
│ └────────┬─────────────────────────────┘ │
│ │ │
│ │ adc_count = 0 ~ 4095 (12-bit) │
│ ▼ │
│ ┌──────────────────────────────────────┐ │
│ │ voltage_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, ◄── 1800 │ │
│ │ adc_count │ │
│ │ ) │ │
│ └────────┬─────────────────────────────┘ │
│ │ │
│ │ voltage_mv = 0 ~ 1800 mV │
│ ▼ │
│ ┌──────────────────┐ │
│ │ return voltage_mv│ │
│ └──────────────────┘ │
│ │
└─────────────────────────────────────────────────────────────────┘
```
***
#### get\_pot\_percentage() Flowchart
```bash
┌─────────────────────────────────────────────────────────────────┐
│ get_pot_percentage() Function │
├─────────────────────────────────────────────────────────────────┤
│ │
│ ┌──────────────────┐ │
│ │ START │ │
│ │ Input: voltage │ │
│ └────────┬─────────┘ │
│ │ │
│ ▼ │
│ ┌──────────────────────────────────────┐ │
│ │ voltage_mv < 0 ? │ │
│ └────────┬──────────────────┬──────────┘ │
│ │ YES │ NO │
│ ▼ ▼ │
│ ┌──────────────────┐ ┌──────────────────────────────────┐ │
│ │ voltage_mv = 0 │ │ voltage_mv > 1800 ? │ │
│ └────────┬─────────┘ └────────┬──────────────┬──────────┘ │
│ │ │ YES │ NO │
│ │ ▼ │ │
│ │ ┌──────────────────┐ │ │
│ │ │voltage_mv = 1800 │ │ │
│ │ └────────┬─────────┘ │ │
│ │ │ │ │
│ └─────────────────────┴──────────────┘ │
│ │ │
│ ▼ │
│ ┌─────────────────────────────────────────┐ │
│ │ │ │
│ │ percentage = (voltage_mv × 100) │ │
│ │ ───────────────── │ │
│ │ VREF (1800) │ │
│ │ │ │
│ └────────────────────┬────────────────────┘ │
│ │ │
│ ▼ │
│ ┌──────────────────────────────────┐ │
│ │ return (uint8_t) percentage │ │
│ │ (0 ~ 100%) │ │
│ └──────────────────────────────────┘ │
│ │
└─────────────────────────────────────────────────────────────────┘
```
***
#### ADC Conversion Diagram
```bash
┌─────────────────────────────────────────────────────────────────┐
│ ADC Conversion Process │
├─────────────────────────────────────────────────────────────────┤
│ │
│ Potentiometer (P15_1) │
│ │ │
│ │ Analog Voltage │
│ │ (0V ~ 1.8V) │
│ ▼ │
│ ┌──────────────────┐ │
│ │ SAR ADC │ │
│ │ 12-bit │ │
│ │ Resolution │ │
│ └────────┬─────────┘ │
│ │ │
│ │ Digital Count │
│ │ (0 ~ 4095) │
│ ▼ │
│ ┌──────────────────────────────────────┐ │
│ │ CountsTo_mVolts() │ │
│ │ │ │
│ │ mV = (count × VREF) / 4096 │ │
│ │ = (count × 1800) / 4096 │ │
│ │ │ │
│ └────────┬─────────────────────────────┘ │
│ │ │
│ │ Voltage in mV │
│ │ (0 ~ 1800 mV) │
│ ▼ │
│ ┌──────────────────────────────────────┐ │
│ │ get_pot_percentage() │ │
│ │ │ │
│ │ % = (mV × 100) / 1800 │ │
│ │ │ │
│ └────────┬─────────────────────────────┘ │
│ │ │
│ │ Percentage │
│ │ (0% ~ 100%) │
│ ▼ │
│ ┌──────────────────┐ │
│ │ Display Output │ │
│ │ "POT: 900 mV | │ │
│ │ 50%" │ │
│ └──────────────────┘ │
│ │
│ ═══════════════════════════════════════════════════════════ │
│ │
│ Examples: │
│ ───────── │
│ Count = 0 → 0 mV → 0% │
│ Count = 1024 → 450 mV → 25% │
│ Count = 2048 → 900 mV → 50% │
│ Count = 3072 → 1350 mV → 75% │
│ Count = 4095 → 1800 mV → 100% │
│ │
└─────────────────────────────────────────────────────────────────┘
```
***
### Program Code ทั้งหมด
```c
/*******************************************************************************
* File Name : main.c
*
* Description : This source file contains the main routine for non-secure
* application in the CM33 CPU
*
*******************************************************************************/
/*******************************************************************************
* Header Files
*******************************************************************************/
#include "cybsp.h"
#include "retarget_io_init.h"
#include
/*******************************************************************************
* Macros
******************************************************************************/
#define CM55_BOOT_WAIT_TIME_USEC (10U)
#define ADC_READ_INTERVAL_MS (100U)
#define SAR_ADC_INDEX (0U)
#define SAR_ADC_SEQUENCER (0U)
#define SAR_ADC_CHANNEL (0U)
#define SAR_ADC_VREF_MV (1800U)
/*******************************************************************************
* Global Variables
*******************************************************************************/
static bool adc_initialized = false;
/*******************************************************************************
* Function Prototypes
*******************************************************************************/
static cy_rslt_t init_adc(void);
static int16_t read_potentiometer_mv(void);
static uint8_t get_pot_percentage(int16_t voltage_mv);
/*******************************************************************************
* Function Name: init_adc
********************************************************************************
* Summary:
* Initializes the SAR ADC using autonomous analog control.
* Sets up interrupt masks and enables autonomous operation.
*
* Parameters:
* none
*
* Return:
* cy_rslt_t - CY_RSLT_SUCCESS if initialization successful
*
*******************************************************************************/
static cy_rslt_t init_adc(void)
{
cy_rslt_t result;
/* Initialize SAR ADC with autonomous analog configuration */
result = Cy_AutAnalog_Init(&autonomous_analog_init);
if (CY_AUTANALOG_SUCCESS != result)
{
return result;
}
/* Set interrupt mask to enable SAR0 result interrupt */
Cy_AutAnalog_SetInterruptMask(CY_AUTANALOG_INT_SAR0_RESULT);
/* Start autonomous control of the ADC */
Cy_AutAnalog_StartAutonomousControl();
adc_initialized = true;
return CY_RSLT_SUCCESS;
}
/*******************************************************************************
* Function Name: read_potentiometer_mv
********************************************************************************
* Summary:
* Reads the potentiometer value from ADC and converts to millivolts.
* Uses the autonomous analog SAR ADC API.
*
* Parameters:
* none
*
* Return:
* int16_t - Voltage in millivolts (0-1800 mV)
*
*******************************************************************************/
static int16_t read_potentiometer_mv(void)
{
int32_t adc_count;
int16_t voltage_mv;
/* Read ADC result (raw counts) */
adc_count = Cy_AutAnalog_SAR_ReadResult(SAR_ADC_INDEX,
CY_AUTANALOG_SAR_INPUT_GPIO,
SAR_ADC_CHANNEL);
/* Convert ADC counts to millivolts */
voltage_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 voltage_mv;
}
/*******************************************************************************
* Function Name: get_pot_percentage
********************************************************************************
* Summary:
* Converts potentiometer voltage to percentage (0-100%).
* Maps the voltage range (0 to VREF_MV) to percentage scale.
*
* Parameters:
* voltage_mv - Input voltage in millivolts
*
* Return:
* uint8_t - Percentage value (0-100)
*
*******************************************************************************/
static uint8_t get_pot_percentage(int16_t voltage_mv)
{
int32_t percentage;
/* Ensure voltage is within valid range */
if (voltage_mv < 0)
{
voltage_mv = 0;
}
else if (voltage_mv > SAR_ADC_VREF_MV)
{
voltage_mv = SAR_ADC_VREF_MV;
}
/* Calculate percentage: (voltage / VREF) * 100 */
percentage = ((int32_t)voltage_mv * 100) / SAR_ADC_VREF_MV;
return (uint8_t)percentage;
}
/*******************************************************************************
* Function Name: main
*******************************************************************************
* Summary:
* Main function - entry point for the ADC potentiometer demo.
*
* This demo reads the potentiometer connected to P15_1 and displays:
* - Raw voltage in millivolts (0-1800 mV)
* - Percentage value (0-100%)
*
* The LED toggles with each ADC reading to indicate activity.
*
* Parameters:
* none
*
* Return:
* int
*
******************************************************************************/
int main(void)
{
cy_rslt_t result = CY_RSLT_SUCCESS;
int16_t voltage_mv;
uint8_t percentage;
/* Initialize the device and board peripherals. */
result = cybsp_init();
/* Board initialization failed. Stop program execution. */
if (CY_RSLT_SUCCESS != result)
{
handle_app_error();
}
/* Enable global interrupts */
__enable_irq();
/* Initialize retarget-io middleware */
init_retarget_io();
/* \x1b[2J\x1b[;H - ANSI ESC sequence for clear screen. */
printf("\x1b[2J\x1b[;H");
printf("***********************************************************\r\n");
printf(" PSOC Edge MCU: Potentiometer ADC \r\n");
printf("***********************************************************\r\n\n");
/* Initialize SAR ADC using helper function */
result = init_adc();
if (CY_RSLT_SUCCESS != result)
{
printf("ADC initialization failed!\r\n");
handle_app_error();
}
/* Inform user about potentiometer connection */
printf("ADC initialized successfully!\r\n");
printf("Reading potentiometer on pin P15_1\r\n");
printf("VREF = %d mV (12-bit resolution)\r\n\n", SAR_ADC_VREF_MV);
/* CY_CM55_APP_BOOT_ADDR must be updated if CM55 memory layout is changed.*/
Cy_SysEnableCM55(MXCM55, CY_CM55_APP_BOOT_ADDR, CM55_BOOT_WAIT_TIME_USEC);
for(;;)
{
/* Read potentiometer voltage using helper function */
voltage_mv = read_potentiometer_mv();
/* Convert to percentage using helper function */
percentage = get_pot_percentage(voltage_mv);
/* Print ADC output in millivolts and percentage */
printf("POT: %4d mV | %3d%%\r\n", voltage_mv, percentage);
/* Toggle user LED to indicate activity */
Cy_GPIO_Inv(CYBSP_USER_LED_PORT, CYBSP_USER_LED_PIN);
/* Delay between ADC readings */
Cy_SysLib_Delay(ADC_READ_INTERVAL_MS);
}
}
/* [] END OF FILE */
```
***
#### ✍️ Exercise
1. **LED Brightness Indicator** : ใช้ POT ควบคุมความเร็วการกระพริบ (Blink Rate) ของ LED
* 0-25%: Blink Rate --> 1000 ms
* 25-50%: Blink Rate --> 500 ms
* 50-75%: Blink Rate --> 250 ms
* 75-100%: Blink Rate --> 100 ms
{% hint style="info" %}
**Hint**
ตัวอย่าง
```c
uint8_t pot_pct = get_pot_percentage();
uint32_t blink_delay;
if (pot_pct < 25) {
blink_delay = 1000; /* Slow blink */ }
else if (pot_pct < 50) {
.
.
.
} else {
...
}
```
{% endhint %}
2. **Threshold Alert** : แจ้งเตือนเมื่อ POT เกิน threshold ที่กำหนด
{% hint style="info" %}
**Hint**
ตัวอย่าง
```c
#define THRESHOLD_PCT (75U)
static bool alert_triggered = false;
for(;;)
{
uint8_t pot_pct = get_pot_percentage();
if (pot_pct >= THRESHOLD_PCT && !alert_triggered)
{
.
.
alert_triggered = true;
}
else if (pot_pct < THRESHOLD_PCT && alert_triggered)
{
.
.
alert_triggered = false;
}
Cy_SysLib_Delay(100);
}
```
{% endhint %}
***
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