ADC Processing and RMS Calculation

Classes
struct	ADC_Sample
	ADC sample with value and associated channel. More...
struct	RMS_FIFO
	Circular buffer for efficient RMS calculation. More...

Functions
void IRAM_ATTR	on_adc_data_ready ()
	Interrupt service routine for completed ADC conversions.
void	task_adquisicion (void *pvParameters)
	ADC data acquisition task with improved multiplexer handling.
void	task_procesamiento (void *pvParameters)
	Sample processing and RMS calculation task.
int	get_rms_history (int channel, float *output_buffer, int count)
	Gets RMS value history for a specific channel.

Variables
const float	CONVERSION_FACTORS [NUM_CHANNELS]
	Channel-specific conversion factors for each ADC channel.
QueueHandle_t	queue_adc_samples
	Communication queue for ADC samples.
RMS_FIFO	fifos [NUM_CHANNELS]
	Array of FIFOs for each measurement channel.
float	rms_history_ch0 [RMS_HISTORY_SIZE]
	RMS value history for channel 0.
float	rms_history_ch1 [RMS_HISTORY_SIZE]
	RMS value history for channel 1.
float	rms_history_ch2 [RMS_HISTORY_SIZE]
	RMS value history for channel 2.
volatile int	rms_history_head = 0
	Write index for RMS histories.
SemaphoreHandle_t	rms_history_mutex
	Mutex for concurrent access protection to RMS histories.
volatile bool	adc_data_ready = false
	ADC data ready flag (ISR).
volatile uint8_t	current_isr_channel = 0
	Current channel in sampling sequence (ISR).
const int	FIFO_SIZE = 320
	Circular FIFO buffer size for RMS calculation.
const int	PROCESS_INTERVAL_MS = 1000
	RMS processing interval in milliseconds.
const int	RMS_HISTORY_SIZE = 100
	RMS value history size for each channel.
const float	CONVERSION_FACTOR = 0.618f
	Global conversion factor (maintained for compatibility).

Detailed Description

Overview

This module implements analog signal acquisition via ADS1015 and the complete flow of:

• ADC sample acquisition in round-robin mode between 3 channels using interrupts.
• Real-time processing with circular FIFOs for efficient RMS calculation.
• RMS value history storage in thread-safe buffers.
• Application of channel-specific conversion factors for individual calibration.

Structure and Components

• Data and configuration
  • ADC_Sample: sample structure with value and associated channel.
  • RMS_FIFO: circular buffer with cumulative sums for incremental calculation.
  • CONVERSION_FACTORS[]: channel-specific calibration factors.
• Acquisition and processing
  • queue_adc_samples: FreeRTOS queue for acquisition → processing transfer.
  • fifos[NUM_CHANNELS]: array of circular FIFOs for each channel.
  • rms_history_ch0/ch1/ch2: independent histories of RMS values.
• Main tasks
  • task_adquisicion: ADC conversion management with improved multiplexer.
  • task_procesamiento: incremental RMS calculation and history update.
  • ISR: on_adc_data_ready() for conversion completion notification.

Main API

• Configuration: FIFO_SIZE, PROCESS_INTERVAL_MS, RMS_HISTORY_SIZE, CONVERSION_FACTORS[].
• Structures: ADC_Sample, RMS_FIFO.
• Data: queue_adc_samples, fifos[], rms_history_ch0/ch1/ch2, rms_history_mutex.
• Functions: task_adquisicion(), task_procesamiento(), get_rms_history(), on_adc_data_ready().

Usage

Flow summary:

1) ADC initialization

• ADS1015 configuration: TWOTHIRDS gain (±6.144V), 3300 SPS speed.
• Interrupt configuration on ALERT pin for completed conversions.
• Creation of queue_adc_samples queue with FIFO_SIZE capacity.
• Initialization of rms_history_mutex mutex for history protection.

2) Sample acquisition

• task_adquisicion executes on core 0 with priority 5.
• Round-robin sequence between channels 0, 1, 2 using explicit multiplexer.
• Direct mapping: channel → MUX configuration (SINGLE_0/SINGLE_1/SINGLE_2).
• ISR on_adc_data_ready() notifies conversion completion via adc_data_ready flag.
• Samples queued in queue_adc_samples with ADC_Sample structure.

3) RMS processing

• task_procesamiento consumes samples from queue on core 0 with priority 3.
• Circular FIFO update with incremental algorithm:
  • Sum maintenance: sum_x (∑x) and sum_x2 (∑x²).
  • Circular buffer with automatic replacement upon reaching FIFO_SIZE=320.
  • Mean calculation: μ = sum_x / count.
  • Variance calculation: σ² = (sum_x2 / count) - μ².
  • RMS value: √σ² with negative variance protection.

4) History management

• RMS calculation every PROCESS_INTERVAL_MS=1000ms.
• Storage in independent circular buffers per channel.
• Thread-safe protection with rms_history_mutex.
• get_rms_history() function for extracting last N values.

5) Channel calibration

• CONVERSION_FACTORS[] array with specific factors:
  • Channel 0: 0.653f
  • Channel 1: 0.679f
    
  • Channel 2: 1.133f
• Applied in dataUpdateTask to compensate sensor differences.
• Allows individual adjustment of measurement ranges and conditioning.

6) Incremental RMS algorithm

• O(1) efficiency for new sample insertion.
• No need to traverse entire buffer for calculation.
• Automatic maintenance of cumulative statistics.
• Robust overflow management in circular buffer.

Warnings and best practices:

• Verify ADS1015 power supply stability for accurate conversions.
• Configure external pullups on I2C lines if communication issues occur.
• Validate ALERT pin connection before enabling interrupts.
• Protect RMS history access with appropriate mutex timeout.
• Calibrate CONVERSION_FACTORS[] according to actual sensor characteristics.
• Monitor processing latency to avoid queue saturation.
• Verify that FIFO_SIZE is sufficient for required analysis window.

Function Documentation

get_rms_history()

int get_rms_history	(	int	channel,
		float *	output_buffer,
		int	count )

Gets RMS value history for a specific channel.

Extracts the last N RMS values in a thread-safe manner using mutex. Values are returned in chronological order (oldest first).

Parameters

channel	Channel number (0, 1 or 2).
output_buffer	Output buffer for RMS values.
count	Number of requested values.

Returns

Number of values actually copied.

on_adc_data_ready()

void IRAM_ATTR on_adc_data_ready

(

)

Interrupt service routine for completed ADC conversions.

Executes when ADS1015 completes a conversion and activates ALERT line.

task_adquisicion()

void task_adquisicion

(

void *

pvParameters

)

ADC data acquisition task with improved multiplexer handling.

Manages ADC conversion sequence in round-robin mode between channels. Implements explicit multiplexer configuration selection for each channel. Enqueues samples in queue_adc_samples for subsequent processing.

Parameters

pvParameters

Task parameters (unused).

Explicit multiplexer configuration selection per channel.

Direct mapping from channel number to ADS1015 multiplexer configuration constant to avoid addressing errors.

task_procesamiento()

void task_procesamiento

(

void *

pvParameters

)

Sample processing and RMS calculation task.

Consumes samples from queue_adc_samples, stores them in circular FIFOs and periodically calculates RMS values using efficient incremental algorithms. Updates RMS history in a thread-safe manner.

Parameters

pvParameters

Task parameters (unused).

Variable Documentation

CONVERSION_FACTOR

const float CONVERSION_FACTOR = 0.618f

Global conversion factor (maintained for compatibility).

Deprecated

Use CONVERSION_FACTORS array for channel-specific factors.

CONVERSION_FACTORS

const float CONVERSION_FACTORS[NUM_CHANNELS]

Initial value:

= {
    0.653f,  
    0.679f,  
    1.133f   
}

Channel-specific conversion factors for each ADC channel.

Enables individual channel calibration to compensate for differences in sensors, signal conditioning or specific measurement ranges.