sensing temperature with a thermocouple / thermocouple

[jaraya]

hello, testing the spi examples of SDK16.0.0 I was trying to read a type k thermocouple with a max31856 on the nRF52840dk board, I made the connections of ss, sck, mosi, miso. The problem is that I don't get thermocouple values, is there another way to read this type of sendor with the nRF52840dk board?

[ovrebekk]

Hi

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

[jaraya]

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?

[ovrebekk]

Hi 

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

[jaraya]

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

[ovrebekk]

Hi 

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

Best regards
Torbjørn

[jaraya]

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.

[ovrebekk]

Hi 

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

[jaraya]

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

[jaraya]

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?

[ovrebekk]

Hi 

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