sensing temperature with a thermocouple / thermocouple

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Thu, 30 Jan 2020 10:00:05 GMT

Which board are you talking about?

The MAX31856 board or the nRF52840DK?

Will the nRF52840DK know when this happens, so that you can run some kind of reset sequence on your MAX31856?

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Wed, 29 Jan 2020 17:28:38 GMT

Hello, I noticed something in the project, when I turn off the board everything is going well, but when I turn on the board again, the MAX31856 stays frozen, I have to remove the MISO and MOSI a few seconds to react, do you know what could be the cause? Should I have any command that closes the SPI to avoid this?

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Wed, 29 Jan 2020 13:33:29 GMT

Thank you, and if I have more doubts if I will open a new ticket

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Wed, 29 Jan 2020 09:56:07 GMT

For the future please open a new ticket if you have questions not directly related to the current one. The devzone system is not well suited for handling long cases with many different questions.

The relationship between the voltage on the input and the reported value depends on several factors, including what reference voltage is used, the bitrate, and the gain setting.

In single ended mode (with the negative input to the ADC set to ground) the result from the ADC is given by the following formula:

RESULT = V_In * (GAIN/REFERENCE) * 2^RESOLUTION

Turn the formula around and you find that the actual voltage (V_In) can be calculated as such:

V_In = RESULT * (REFERENCE/GAIN) / (2^RESOLUTION)

For more information about this please refer to this chapter in the product specification.

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Tue, 28 Jan 2020 14:12:07 GMT

One more query, now I have to fill in the analog data of a gas sensor, in the SAADC example data and in the documentation I can't find the equivalent of how much each bit is worth in real volts.

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Mon, 27 Jan 2020 13:50:56 GMT

While it's odd the SPIM didn't work it's good to hear you found a solution 🙂

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Fri, 24 Jan 2020 22:36:07 GMT

Hello, I already solved the problem, I changed from the SPIM example to the one of SPI and with this I got a good reading of the data and with these I already managed to calculate the thermocouple temperature

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Fri, 24 Jan 2020 13:21:25 GMT

Do you have a scope trace of the SPI signals between the two devices, so I can see what is going on over the bus?

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Wed, 22 Jan 2020 22:36:03 GMT

I elaborated this example, at the moment it is done only to obtain the varibals stored in the MAX31856, but, when I was going to elaborate the other calculations to take out the temperature the data of the MAX did not arrive anymore. Do you have any advice that could be wrong? , I already checked the circuit connections and they are well connected.

#include "nrfx_spim.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 NRFX_SPIM_SCK_PIN  3
#define NRFX_SPIM_MOSI_PIN 4
#define NRFX_SPIM_MISO_PIN 28
#define NRFX_SPIM_SS_PIN   29
#define NRFX_SPIM_DCX_PIN  30

#define Cold_Junction_Resolution  0.015625
#define TC_Resolution             0.0078125  

#define MAX31856_WRITE            0x80
#define MAX31856_READ             0x00

#define Average_1_Bit             0x0F
#define Average_2                 0x10
#define Average_4                 0x20
#define Average_8                 0x30
#define Average_16                0x40

#define No_Fault_Mask             0x02
#define Interrupt_Mode            0x04

#define OC_Fault_Disable_Bit      0xCF
#define OC_Fault_Enable_1         0x10
#define OC_Fault_Enable_2         0x20
#define OC_Fault_Enable_3         0x30

#define TC_TypeB_Bit              0xF0
#define TC_TypeE                  0x01
#define TC_TypeJ                  0x02
#define TC_TypeK                  0x03
#define TC_TypeN                  0x04
#define TC_TypeR                  0x05
#define TC_TypeS                  0x06
#define TC_TypeT                  0x07
#define VM_Gain8                  0x80
#define VM_Gain16                 0xC0

#define MAX31856_cr0_REG          0x00
#define MAX31856_cr0_1SHOT        0x40
#define Stop_Conversion_Bit       0x3F
#define MAX31856_cr0_50HZ         0x01
#define MAX31856_CHIP_SELECT      0
#define MAX31856_cr0_FAULTCLR     0x02
#define MAX31856_CJTO             0x09
#define MAX31856_CJTH             0x0A
#define MAX31856_CJTL             0x0B
#define MAX31856_LTCBH            0x0C
#define MAX31856_LTCBM            0x0D
#define MAX31856_LTCBL            0x0E

#define SPI_INSTANCE  3                                           /**< SPI instance index. */
static const nrfx_spim_t spi = NRFX_SPIM_INSTANCE(SPI_INSTANCE);  /**< SPI instance. */
static volatile bool spi_xfer_done;  /**< Flag used to indicate that SPI instance completed the transfer. */
static uint8_t       m_tx_buf[4];  /**< TX buffer. */
static uint8_t       m_rx_buf[5];  /**< RX buffer. */
static const uint8_t m_length = sizeof(m_tx_buf);

uint8_t Max31856_cr0, Max31856_cr1;
int temp, offset;
float cold_junction_temperature, ctemp;

void spim_event_handler(nrfx_spim_evt_t const * p_event, void * p_context)
{
    spi_xfer_done = true;
    NRF_LOG_INFO("Transfer completed.");

    if (m_tx_buf[3] == 11){
        printf("RX1 = %d\n",m_rx_buf[0]);
        printf("RX1 = %d\n",m_rx_buf[1]);
        printf("RX1 = %d\n",m_rx_buf[2]);
        printf("RX1 = %d\n",m_rx_buf[3]);
        NRF_LOG_INFO(" Received:");
        NRF_LOG_HEXDUMP_INFO(m_rx_buf, strlen((const char *)m_rx_buf)); 
        
    }
    else if (m_tx_buf[3] == 14){
        printf("RX2 = %d\n",m_rx_buf[0]);
        printf("RX2 = %d\n",m_rx_buf[1]);
        printf("RX2 = %d\n",m_rx_buf[2]);
        printf("RX2 = %d\n",m_rx_buf[3]);
        NRF_LOG_INFO(" Received:");
        NRF_LOG_HEXDUMP_INFO(m_rx_buf, strlen((const char *)m_rx_buf));
    }
}

int confi(){
      spi_xfer_done = false;
      Max31856_cr0 = OC_Fault_Enable_1|MAX31856_cr0_50HZ|Interrupt_Mode;
      Max31856_cr1 = Average_1_Bit|TC_TypeK;

      m_tx_buf[0] = MAX31856_WRITE;
      m_tx_buf[1] = Max31856_cr0;
      m_tx_buf[2] = Max31856_cr1;
      m_tx_buf[3] = No_Fault_Mask;
      nrfx_spim_xfer_desc_t xfer_desc=NRFX_SPIM_XFER_TRX(m_tx_buf, m_length, m_rx_buf,m_length);
      APP_ERROR_CHECK(nrfx_spim_xfer_dcx(&spi, &xfer_desc, 0, 15));
}

int oneshoot(){
      spi_xfer_done = false;
      Max31856_cr0 = Stop_Conversion_Bit;
      m_tx_buf[0] = MAX31856_WRITE;
      m_tx_buf[1] = MAX31856_cr0_REG;
      m_tx_buf[2] = Max31856_cr0|MAX31856_cr0_1SHOT|MAX31856_cr0_FAULTCLR;
      nrfx_spim_xfer_desc_t xfer_desc=NRFX_SPIM_XFER_TRX(m_tx_buf, m_length, m_rx_buf,m_length);
      APP_ERROR_CHECK(nrfx_spim_xfer_dcx(&spi, &xfer_desc, 0, 15));
      nrf_delay_ms(250);
}

int CJT(){
      
      spi_xfer_done = false;
      m_tx_buf[0] =  MAX31856_READ;
      m_tx_buf[1] = MAX31856_READ|MAX31856_CJTO;
      m_tx_buf[2] = MAX31856_READ|MAX31856_CJTH;
      m_tx_buf[3] = MAX31856_READ|MAX31856_CJTL;
      nrfx_spim_xfer_desc_t xfer_desc=NRFX_SPIM_XFER_TRX(m_tx_buf, m_length, m_rx_buf, m_length);
      APP_ERROR_CHECK(nrfx_spim_xfer_dcx(&spi, &xfer_desc, 0, 15));
      printf("CJTO = %d\n",m_rx_buf[1]);
      printf("CJTH = %d\n",m_rx_buf[2]);
      printf("CJTL = %d\n",m_rx_buf[3]);}

int LTCB(){
      spi_xfer_done = false;
      m_tx_buf[0] = MAX31856_READ;
      m_tx_buf[1] = MAX31856_READ | MAX31856_LTCBH;
      m_tx_buf[2] = MAX31856_READ | MAX31856_LTCBM;
      m_tx_buf[3] = MAX31856_READ | MAX31856_LTCBL;
      nrfx_spim_xfer_desc_t xfer_desc=NRFX_SPIM_XFER_TRX(m_tx_buf, m_length, m_rx_buf,m_length);
      APP_ERROR_CHECK(nrfx_spim_xfer_dcx(&spi, &xfer_desc, 0, 15));
      printf("LTCH = %d\n",m_rx_buf[1]);
      printf("LTCM = %d\n",m_rx_buf[2]);
      printf("LTCL = %d\n",m_rx_buf[3]);
      return (spi_xfer_done); }

int main(void){
    bsp_board_init(BSP_INIT_LEDS);

    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();

    nrfx_spim_config_t spi_config = NRFX_SPIM_DEFAULT_CONFIG;
    spi_config.frequency      = NRF_SPIM_FREQ_4M;
    spi_config.ss_pin         = NRFX_SPIM_SS_PIN;
    spi_config.miso_pin       = NRFX_SPIM_MISO_PIN;
    spi_config.mosi_pin       = NRFX_SPIM_MOSI_PIN;
    spi_config.sck_pin        = NRFX_SPIM_SCK_PIN;
    spi_config.dcx_pin        = NRFX_SPIM_DCX_PIN;
    spi_config.mode           = NRF_SPIM_MODE_3;
    spi_config.use_hw_ss      = true;
    spi_config.ss_active_high = false;
    APP_ERROR_CHECK(nrfx_spim_init(&spi, &spi_config, spim_event_handler, NULL));
    NRF_LOG_INFO("NRFX SPIM example started.");

    while (1)
    {
        confi();
        oneshoot();
        CJT();
        LTCB();

        while (!spi_xfer_done){__WFE();}

        NRF_LOG_FLUSH();

        bsp_board_led_invert(BSP_BOARD_LED_0);
        nrf_delay_ms(2000);
    }
}

RE: sensing temperature with a thermocouple / thermocouple

awneil — Fri, 17 Jan 2020 17:00:45 GMT

The MAX31856 neither knows nor cares what the SPI master is.

All the MAX31856 sees is the SPI lines - SDI, SDO, SCK, and CS.

Similarly, the nRF52 neither knows nor cares what the SPI slave is: it just drives the SPI lines - MISO, MOSI, SCK, CS in accordance with your code's instructions.

So you just need to ensure that the nRF52 is driving those lines as shown in the MAX datasheet

See the figures on page 16 of the MAX datasheet.

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Fri, 17 Jan 2020 15:21:13 GMT

This is the datasheet link datasheets.maximintegrated.com/.../MAX31856.pdf, the examples I used to work on the Raspberry always existed the SPI command to write and read, this is one of the examples to use as a guide github.com/.../max31856.c, www.maximintegrated.com/.../ tb_tab2 and www.raspberrypi.org/.../viewtopic.php, the latter use it as a base to modify it with data from the other two codes. What is common in these codes is that there is a command to write and read data from the MAX31856 records through SPI and in the documentation of nRF52840DK I have not found it. So my question is, if the command or function exists in this model?

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Fri, 17 Jan 2020 09:11:19 GMT

You mean how you can set up the SPI to use your particular sensor?

There is really no shortcuts to this unless there are some examples online that does it. I usually find it easiest just to find the commands you need in the MAX31856 datasheet, and implement those commands as detailed in the datasheet.

An alternative way is to find a driver online (such as this one) that is made for a different MCU architecture, and port it to run on the nRF52. That typically means that any code accessing GPIO's or the SPI interface will have to be changed to use the Nordic drivers.

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Wed, 15 Jan 2020 21:00:33 GMT

Yes, but, how can I write and read data from a component such as MAX31856 that is responsible for hosting the thermocouple reading data. I can write certain addresses, 0x00, 0x0A ...., and then read others that contain thermocouple reading data. In the examples of SPI I do not find one that will guide me in this case.

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Tue, 14 Jan 2020 13:28:35 GMT

Sorry for the late response, I have been out of office for the last month or so.

Do you still need help with this?

The incoming data is stored in the m_rx_buf buffer, which is written to the log inside the spi_event_handler() function. Is this not what you are looking for?

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Mon, 09 Dec 2019 16:47:03 GMT

Another question regarding the spi or spim example code, how can I pass it from TEST_STRING to show me the values given by the miso pin?

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Fri, 06 Dec 2019 09:12:21 GMT

Have you looked into this example?

https://github.com/engineertype/MAX31856/tree/master/MAX31856

It looks pretty straight forward, but you will need to replace the GPIO and SPI functions with the Nordic ones, and implement a function based C interface rather than a class based C++ interface.

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Thu, 05 Dec 2019 15:21:07 GMT

Hello, I found this example not Nordic, but I am getting complicated to adapt it, do you have any tips for it?

https://www.maximintegrated.com/en/products/sensors/MAX31856.html/tb_tab2

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Thu, 05 Dec 2019 14:18:09 GMT

We don't have any examples for this type of sensor unfortunately.

Either you would have to find some non-nordic example and adapt it to the nRF52840, or implement something from scratch based on the MAX31856 datasheet.

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Tue, 03 Dec 2019 22:21:08 GMT

I have another doubt, to read a type K thermocouple with a max31856 through SPI, which example could be useful to read the data sent by the sensor?

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Wed, 27 Nov 2019 12:40:34 GMT

Do you mean the SPI example in the SDK?

In this example the SPI interface is configured through the spi_config struct.

The example uses mostly default settings, but you are free to change all the fields in the spi_config struct before calling nrf_drv_spi_init(..), such as the mode or bit_order fields.

Best regards
Torbjørn

RE: sensing temperature with a thermocouple / thermocouple

jaraya — Tue, 26 Nov 2019 22:29:09 GMT

Hi, I have reviewed the SPI example but I can't find where to change the mode and frequency, could you guide me to test those changes?

RE: sensing temperature with a thermocouple / thermocouple

ovrebekk — Tue, 26 Nov 2019 15:02:15 GMT

Have you made sure to configure the SPI in the nRF52840 with the right mode and frequency to work with your sensor?

Have you tried to probe the SPI lines with a scope or logic analyzer to verify that the communication looks OK?

Best regards
Torbjørn