SPI_with_ADC_Data_issue

[DG]

Hi  

i am reading ADC121S101CIMF using spi but i not getting correct value at some different voltage .which is mention in below file. and input given by potentiometer ( 5 k ohm ) in analog pin of adc 

 1.output file

ADC121S101_with_nrf52840.xlsx

2 block diagram of setup 

 spi code:

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#include "nrf_drv_spi.h"
#include "app_util_platform.h"
#include "nrf_gpio.h"
#include "nrf_delay.h"
#include "boards.h"
#include "app_error.h"
#include <string.h>
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define SPI_INSTANCE 0 /**< SPI instance index. */
static const nrf_drv_spi_t spi = NRF_DRV_SPI_INSTANCE(SPI_INSTANCE); /**< SPI instance. */
static volatile bool spi_xfer_done; /**< Flag used to indicate that SPI instance completed the transfer. */

#define TEST_STRING "Nordic"
//static uint8_t m_tx_buf[] = TEST_STRING; /**< TX buffer. */
//static uint8_t m_rx_buf[sizeof(TEST_STRING) + 1]; /**< RX buffer. */
//static const uint8_t m_length = sizeof(m_tx_buf); /**< Transfer length. */

/*
uint8_t m_tx_buf[255] = {1,2,3,4,5,6,7,9,10,11,12,13,14,15,16,17,18,19,20,8};
uint8_t m_rx_buf[255] = {0};
uint8_t m_length =255;
*/
uint8_t m_tx_buf[2] = {0,0};
uint8_t m_rx_buf[2] = {0};
uint8_t m_length =2;

uint8_t spi_data[8] = {0,0,0,0,0,0,0,0};
uint8_t spi_data1[8] = {0,0,0,0,0,0,0,0};
uint8_t spi_data2[8] = {0,0,0,0,0,0,0,0};
uint8_t spi_data3[8] = {0,0,0,0,1,0,1,1};

//uint8_t m_rx_buf[255] = {0};
//uint8_t m_length =255;

uint16_t rxbuff[255];
/**
* @brief SPI user event handler.
* @param event
*/
void spi_event_handler(nrf_drv_spi_evt_t const * p_event,
void * p_context)
{
spi_xfer_done = true;
//NRF_LOG_INFO("Transfer completed.");
if (m_rx_buf[0] != 0)
{
//NRF_LOG_INFO(" Received:");
//NRF_LOG_HEXDUMP_INFO(m_rx_buf, strlen((const char *)m_rx_buf));
}
}

int read_aadc_data()
{
uint16_t output=0;
uint8_t lsb[1]={0};
volatile uint8_t msb[2]={0,0};
uint8_t data[2]={0,0};
uint8_t data1[2]={0,0};

//nrf_gpio_pin_clear(SPI_SS_PIN);
spi_xfer_done = false;
APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi,&data[0],2,msb,2));
while (!spi_xfer_done)
{
// NRF_LOG_FLUSH();
__WFE();
}
// printf("msb=%d\n",msb[0]);
// printf("msb=%d\n",msb[1]);
output = ((msb[0] << 8)|msb[1]);
//nrf_gpio_pin_set(SPI_SS_PIN);
/*
APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi,&data1[0],1,lsb,1));

while (!spi_xfer_done)
{
// NRF_LOG_FLUSH();
__WFE();
}
printf("lsb=%d\n",lsb[0]);
nrf_gpio_pin_set(SPI_SS_PIN);
//nrf_gpio_pin_clear(SPI_SS_PIN);

output=0;
output = ((msb[0] << 8)|lsb[0]);
//nrf_delay_us(1);
// printf("output=%d\n",output);
*/
return output;
}

int main(void)
{

nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
spi_config.ss_pin = SPI_SS_PIN;
spi_config.miso_pin = SPI_MISO_PIN;
spi_config.mosi_pin = SPI_MOSI_PIN;
spi_config.sck_pin = SPI_SCK_PIN;
APP_ERROR_CHECK(nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL));
int i=0;
while(1)
{


uint16_t adcOut=0;
float value=0.0;

memset(data_buff,0,344);
adcOut=0;
adcOut=read_aadc_data();
printf("%d,",adcOut);
/*
i=i+1;
if(i==10)
{
printf("\n");
i=0;
}
*/
//nrf_delay_ms(1000000);

nrf_delay_us(500);

}


}

 

can you guide why i am getting multiple value and wrong value and same data reading from arduino board i am getting correct value .

BR 

DG 

[Jørgen Holmefjord]

Hi,

Have you scoped the SPI lines in and out of the level shifter, to see if the data is changed somewhere between the ADC and the nRF chip?

Which SDK version are you using? Can you upload the sdk_config.h file from your project?

Best regards,
Jørgen

[DG]

Hi Jorgen ,

I am using SDK Version 15 

3644.sdk_config.h

case 1  :  Spi clock line Yellow line output( 5 v )   and  blue line input ( 3 V ) and i am working on 500KHz and i try from                    125Khz to 8M but getting same data  

Case 2 : SPI data out line (MISO) same  Yellow line output( 5 v )   and  blue line input ( 3 V )

case 3 :  SPI CS line same  Yellow line output( 5 v )   and  blue line input ( 3 V )

[DG]

Did you got any error in sdk_config.h 

[Jørgen Holmefjord]

The signals looks a bit strange. Are you sure that the level shifter is working properly?

Do the Arduino test show similar signal behavior? Is Arduino test also using level shifter?

You could try to increase the drive strength of the MISO/SCK pins to high drive, to make the signals more robust. This needs to be done after initialization of the SPI driver.

[DG]

Hello,

Yes we have verified the input and the output side of the level shifter using a logic analyser.

No the arduino shows the results as we expect it and since the sensor as well as the ARduino both are 5V TTL compatible we don't need a level shifter.

After the above two responses do you think that increasing the drive strength will make a difference?

DG

[Jørgen Holmefjord]

Yes, I would still suggest that you try to increase the drive strength.

It seems that the ADC can also be run at 3.3V/down to 2.7V, if you could test it out without the level shifter (or get a breakout board of the ADC for 3.3V logic).

[DG]

Dear Jørgen Holmefjord 

Okay we will increase the drive strength and check.

The ADC can run at 3.3V down to 2.7V but the device generating the data (in this case the sensor) has a 5V compatible output. Hence we have taken the input into the ADC for 5V and then the output at 5V TTL on the SPI, converted it with a level shifter to 3.3V TTL and then taken that as an input into the nrf52840.

For the Arduino we have a 5V TTL output of the ADC going to the Arduino over SPI. That is the only difference.

And like we suggested earlier the 5V TTL side and the 3.3V TTL side of the level shifter have both been checked on a logic analyser and the data is identical.

DG

[DG]

drive strength is working ,now i am getting correct value,thank you so much for supporting