MAX30101 I2C communication with nRF52 - DK

Question

Hi, I'm currently designing a system which requires Heart Rate monitorization and I'm using the MAX30101 chip to do so. I will be using I2C communication and, therefore, based my code on the twi_sensor example for the nRF52 -DK dev kit. However, I just can not get any values from the sensor. Can anybody help me understand what I'm doing wrong? Thanks in advance. #include <stdio.h>
#include "boards.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "nrf_drv_twi.h"
#include "nrf_delay.h"


#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

/* TWI instance ID. */
#define TWI_INSTANCE_ID 0

/* Common addresses definition for temperature sensor. */
#define LM75B_ADDR (0x90U >> 1)

#define MAX30101_ADDRESS 0x57
#define MAX30101_CONF_REG 0x09
#define MAX30101_MODE_HR 0x02
#define MAX30101_MODE_SPO2 0x03
#define MAX30101_FIFO_DATA 0x07
#define MAX30101_FIFO_WR_PT 0x04
#define MAX30101_FIFO_RD_PT 0x06

#define LM75B_REG_TEMP 0x00U
#define LM75B_REG_CONF 0x01U
#define LM75B_REG_THYST 0x02U
#define LM75B_REG_TOS 0x03U

/* Mode for LM75B. */
#define NORMAL_MODE 0U

/* Indicates if operation on TWI has ended. */
static volatile bool m_xfer_done = false;

/* TWI instance. */
static const nrf_drv_twi_t m_twi = NRF_DRV_TWI_INSTANCE(TWI_INSTANCE_ID);

/* Buffer for samples read from temperature sensor. */
static uint8_t m_sample;

static uint8_t m_wr_ptr, m_rd_ptr, m_num_samples;

static uint8_t tx_fifo[2];

/**
 * @brief Function for setting active mode on MMA7660 accelerometer.
 */
void LM75B_set_mode(void)
{
 ret_code_t err_code;

 /* Writing to LM75B_REG_CONF "0" set temperature sensor in NORMAL mode. */
 uint8_t reg[2] = {MAX30101_CONF_REG, MAX30101_MODE_SPO2};
 err_code = nrf_drv_twi_tx(&m_twi, MAX30101_ADDRESS, reg, sizeof(reg), false);
 APP_ERROR_CHECK(err_code);
 while (m_xfer_done == false);

 /* Writing to pointer byte. */
 reg[0] = MAX30101_FIFO_WR_PT;
 m_xfer_done = false;
 err_code = nrf_drv_twi_tx(&m_twi, MAX30101_ADDRESS, reg, 1, false);
 APP_ERROR_CHECK(err_code);
 while (m_xfer_done == false);
 err_code = nrf_drv_twi_rx(&m_twi, MAX30101_ADDRESS, &m_wr_ptr, sizeof(m_wr_ptr));
 APP_ERROR_CHECK(err_code);
 while (m_xfer_done == false);
}

/**
 * @brief Function for handling data from temperature sensor.
 *
 * @param[in] temp Temperature in Celsius degrees read from sensor.
 */
__STATIC_INLINE void data_handler(uint8_t temp)
{
 NRF_LOG_INFO("Values SpO2: %d .", temp);
}

/**
 * @brief TWI events handler.
 */
void twi_handler(nrf_drv_twi_evt_t const * p_event, void * p_context)
{
 switch (p_event->type)
 {
 case NRF_DRV_TWI_EVT_DONE:
 if (p_event->xfer_desc.type == NRF_DRV_TWI_XFER_RX)
 {
 data_handler(m_sample);
 }
 m_xfer_done = true;
 break;
 default:
 break;
 }
}

/**
 * @brief UART initialization.
 */
void twi_init (void)
{
 ret_code_t err_code;

 const nrf_drv_twi_config_t twi_lm75b_config = {
 .scl = ARDUINO_SCL_PIN,
 .sda = ARDUINO_SDA_PIN,
 .frequency = NRF_DRV_TWI_FREQ_100K,
 .interrupt_priority = APP_IRQ_PRIORITY_HIGH,
 .clear_bus_init = false
 };

 err_code = nrf_drv_twi_init(&m_twi, &twi_lm75b_config, twi_handler, NULL);
 APP_ERROR_CHECK(err_code);

 nrf_drv_twi_enable(&m_twi);
}

/**
 * @brief Function for reading data from temperature sensor.
 */
static void read_sensor_data()
{
 ret_code_t err_code;
 
 m_xfer_done = false;

 /* Writing to pointer byte. */
 tx_fifo[0] = MAX30101_FIFO_RD_PT;
 m_xfer_done = false;
 err_code = nrf_drv_twi_tx(&m_twi, MAX30101_ADDRESS, tx_fifo, 1, false);
 APP_ERROR_CHECK(err_code);
 while (m_xfer_done == false);

 /* Read 1 byte from the specified address - skip 3 bits dedicated for fractional part of temperature. */
 err_code = nrf_drv_twi_rx(&m_twi, MAX30101_ADDRESS, &m_sample, sizeof(m_sample));
 APP_ERROR_CHECK(err_code);
}

/**
 * @brief Function for main application entry.
 */
int main(void)
{
 APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
 NRF_LOG_DEFAULT_BACKENDS_INIT();

 NRF_LOG_INFO("
TWI sensor example started.");
 NRF_LOG_FLUSH();

 twi_init();
 NRF_LOG_INFO("
I2C Communication initialized.");
 NRF_LOG_FLUSH();

 LM75B_set_mode();
 NRF_LOG_INFO("
MAX30101 Initialized.");
 NRF_LOG_FLUSH();

 while (true)
 {
 nrf_delay_ms(500);

 do
 {
 __WFE();
 }while (m_xfer_done == false);

 read_sensor_data();
 NRF_LOG_FLUSH();
 }
}

Gabriel Silva · Accepted Answer

My initialization was not correct, there were a lot of configurations missing. The following code is the initialization: void MAX30101_init (void)
{
 //Initialization and Configuration of MAX30101
 MAX30101_regWR(MAX30101_INT_EN_1, 0xC0);
 MAX30101_regWR(MAX30101_INT_EN_2, 0x00);
 
 MAX30101_regWR(MAX30101_FIFO_WR_PT, 0x00);
 MAX30101_regWR(MAX30101_OVF_CNT, 0x00);
 MAX30101_regWR(MAX30101_FIFO_RD_PT, 0x00);

 MAX30101_regWR(MAX30101_FIFO_CONF, 0x1F);
 MAX30101_regWR(MAX30101_CONF_REG, 0x03); //0x02 - HR; 0x03 - SpO2; 0x07 - Multi_LED
 MAX30101_regWR(MAX30101_SPO2_CONF, 0x27);
 MAX30101_regWR(LED1_PA, 0x3F); // LED1 - RED
 //MAX30101_regWR(LED2_PA, 0x3F); // LED2 - IR
 //MAX30101_regWR(LED3_PA, 0x3F); // LED3 - GREEN
 //MAX30101_regWR(LED4_PA, 0x3F); // LED4 - GREEN

 MAX30101_regRD(MAX30101_FIFO_WR_PT, &m_wr_ptr);
 MAX30101_regRD(MAX30101_FIFO_RD_PT, &m_rd_ptr);

 NRF_LOG_INFO("Initialization and Configuration of MAX30101 done");
 NRF_LOG_FLUSH();
}

Right now I'm trying to readthe values from the FIFO where the data is storred, on the MAX30101. The values that I'm getting don't make much sense I think.