Not able to get serial data from ads1293 sensor using nRF52833

[Suryalakshmi]

Hi, I am working on project to obtain ecg data via bluetooth. But before that I was trying to see whether I could obtain ECG signals serially through nrf52833. And I tried a lot but in segger RTT viewer, I am only seeing zeros. My sensor is ads1293 breakout board from protocentral and this one works fine because I have already used it with my Arduino UNO and I was able to get the signal. But when connected with nRF52833, I am not getting any values. What should I do?

#include <stdio.h>
#include "nrf_drv_spi.h"
#include "nrf_gpio.h"
#include "nrf_delay.h"
#include "app_error.h"
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

/* -------- PIN DEFINITIONS -------- */

#define DRDY_PIN 11
#define CS_PIN 12
#define SCK_PIN 13
#define MISO_PIN 14
#define MOSI_PIN 15

/* -------- ADS1293 REGISTERS -------- */

#define REG_CONFIG 0x00
#define REG_SAMPLING 0x21
#define REG_CH_CNFG 0x2F
#define REG_CMDET_EN 0x12
#define REG_RLD_SEL 0x20
#define REG_RLD_CNFG 0x1F

#define REG_CH1_H 0x37
#define REG_CH2_H 0x3A
#define REG_CH3_H 0x3D

#define REG_REVID 0x40
#define REG_STATUS 0x41

static const nrf_drv_spi_t spi = NRF_DRV_SPI_INSTANCE(0);

/* -------- SPI BYTE TRANSFER -------- */

uint8_t spi_transfer(uint8_t data)
{
uint8_t rx;

APP_ERROR_CHECK(
nrf_drv_spi_transfer(&spi, &data, 1, &rx, 1)
);

return rx;
}

/* -------- REGISTER WRITE -------- */

void writeRegister(uint8_t addr, uint8_t value)
{
nrf_gpio_pin_clear(CS_PIN);

spi_transfer(addr);
spi_transfer(value);

nrf_gpio_pin_set(CS_PIN);
}

/* -------- REGISTER READ -------- */

uint8_t readRegister(uint8_t addr)
{
uint8_t val;

nrf_gpio_pin_clear(CS_PIN);

spi_transfer(addr | 0x80);
val = spi_transfer(0x00);

nrf_gpio_pin_set(CS_PIN);

return val;
}

/* -------- READ 24 BIT ECG -------- */

int32_t read24(uint8_t reg)
{
int32_t value = 0;

nrf_gpio_pin_clear(CS_PIN);

spi_transfer(reg | 0x80);

value |= ((int32_t)spi_transfer(0x00) << 16);
value |= ((int32_t)spi_transfer(0x00) << 8);
value |= ((int32_t)spi_transfer(0x00));

nrf_gpio_pin_set(CS_PIN);

/* sign extension */

if (value & 0x800000)
value |= 0xFF000000;

return value;
}

/* -------- MAIN -------- */

int main(void)
{
/* LOG INIT */

NRF_LOG_INIT(NULL);
NRF_LOG_DEFAULT_BACKENDS_INIT();

NRF_LOG_INFO("ADS1293 ECG Start");

/* GPIO SETUP */

nrf_gpio_cfg_output(CS_PIN);
nrf_gpio_cfg_input(DRDY_PIN, NRF_GPIO_PIN_NOPULL);

nrf_gpio_pin_set(CS_PIN);

/* SPI CONFIG */

nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;

spi_config.sck_pin = SCK_PIN;
spi_config.mosi_pin = MOSI_PIN;
spi_config.miso_pin = MISO_PIN;

spi_config.frequency = NRF_DRV_SPI_FREQ_1M;
spi_config.mode = NRF_DRV_SPI_MODE_1;
spi_config.bit_order = NRF_DRV_SPI_BIT_ORDER_MSB_FIRST;

APP_ERROR_CHECK(
nrf_drv_spi_init(&spi, &spi_config, NULL, NULL)
);

nrf_delay_ms(100);

/* -------- SPI TEST -------- */

uint8_t id = readRegister(REG_REVID);
NRF_LOG_INFO("REV ID: %d", id);

uint8_t status = readRegister(REG_STATUS);
NRF_LOG_INFO("STATUS: %d", status);

NRF_LOG_FLUSH();

/* -------- CONFIGURE ADS1293 -------- */

writeRegister(REG_SAMPLING, 0x05); // sampling rate
writeRegister(REG_CH_CNFG, 0x30); // channel routing

writeRegister(REG_CMDET_EN, 0x01); // common mode detect
writeRegister(REG_RLD_SEL, 0x07); // RLD electrode select
writeRegister(REG_RLD_CNFG, 0x04); // enable RLD

writeRegister(REG_CONFIG, 0x01); // start conversion

nrf_delay_ms(10);

NRF_LOG_INFO("ECG Streaming Started");

/* -------- ECG LOOP -------- */

while (true)
{
if (nrf_gpio_pin_read(DRDY_PIN) == 0)
{
int32_t ch1 = read24(REG_CH1_H);
int32_t ch2 = read24(REG_CH2_H);
int32_t ch3 = read24(REG_CH3_H);

NRF_LOG_INFO("%d,%d,%d", ch1, ch2, ch3);
NRF_LOG_FLUSH();
}
}
}
This is the code that I am using. 

[Kazi Afroza Sultana]

Hello,

Pin P0.12 and P0.11 are used for trace buffer pin also. You have ECG project, You are not actively using trace but debugger may automatically enable it during debug session, that can potentially interfere with the SPI CS signal. You can try to use another available pin for CS?

Thanks.

BR

Kazi

[Suryalakshmi]

I changed CS pin from P0.11 To P0.13. But it didn't made any changes. Still SPI is not communicating

[hmolesworth]

If you see nothing on MOSI, perhaps try adding:

   nrf_gpio_pin_set(MOSI_PIN);
   nrf_gpio_cfg_output(MOSI_PIN);

SPI transfers data in via MISO every clock cycle, so when sending a command byte and receiving a data byte 16 clock cycles are used and so 2 bytes are received with the required data in the 2nd byte, not the first.

Try changing to 2-byte receive, something like this:

uint8_t spi_transfer(uint8_t data)
{
  uint8_t rx[2];
  APP_ERROR_CHECK(
    nrf_drv_spi_transfer(&spi, &data, 1, &rx, 2)
  );
  return rx[1];
}

Also not sure but the ADS1293 might require a command to start the clock

[Suryalakshmi]

I tried so much. Still no impovement. Now I suspect whether if it is a software issue. There are many deep switches in the nrf52833 board. What should be there status? Currently the way I have kept them allows me to connect to J link and flash codes in my board. Does the configuration changes or something during SPI communication?

[Turbo J]

What NRF52833 board are you talking about? The DK is set up correctly when you can flash and debug your code.

No idea why your SPI communication fails - you will need to use some kind of oscilloscope or logic analyser (LA) here. I still suspect that the TI ADS chip just refuses to talk to you at all.

[Suryalakshmi]

I was talking about the nRF52833 DK.  I used oscilloscope but both MOSI and MISO are flat. I am trying to find out why it's happening.

[Turbo J]

MOSI misconfigured or otherwise in use on the DK. Try a different pin. Note that there are quite a few connected to other hardware and should not be used externally.