Actions
Forum Thread Details
  • Replies 1 reply
  • Subscribers 416 subscribers
  • Views 488 views
  • Users 0 members are here
Related

Data Logging over SPI onto SD Shield

e14 Contributor

So I have a project that has run into a snare on me. I have to data log 4 thermocouples for a period of time and want to record that data onto an SD card.

 

So I am using an Arduino Uno with (4) Adafruit MAX31855 Breakout boards and an SD Shield from https://www.manylabs.org/product/G0119/

 

So individually I can read the 4 Thermocouple boards in serial over the SPI bus using 4 pins for Chip Select. And it dosent seem to matter which ones I have changed them around to no effect (6, 7, 8, and 9). Same with the SD shield I can read and write to the card no problem at all, but chip select is hard wired to pin 10 on this matching the board default. I should note when I tested these independantly,  I used the default pins on the board for MOSI (11), MISO (12), and SCLK (13) for both setups. I am also using a real world clock board but thats not related as it communicates over I2C.

 

This is where my snare comes in, if I plug the SD shield into the Uno and plug then plug the thermocouple chip select pins, clock, and slave out pins (in the same spots) to the header pins on the SD shield. The logging and code works fine but all 4 of the Thermocouples all read out as zero *C. It is not a wiring issue beause if I purposely disconnect a chip select pin out, the serial print out on that specific thermocouple gives me my error loop. The other 3 continue to read at zero so everything is wired correctly. Everything is dancing, I just cant seem to get it all going on the same page of music. Any tips?

 

EDIT: Oh, btw, I am using an auxiliary power as well as USB. I know the 500 mAh over USB isnt going to cut it. Code is also added now too. The 1st file is the code that simply reads out the thermocouple temperatures in the serial monitor. And the 2nd is that code with the attempt to data log it. you'll note the TC chip select pins are moved around, but it dosent matter they wont work even where they were originally.

Attachments:
TC Data Logging Attempt.ino.zip
Read TCs (Serial).ino.zip

  • So after digging further into this and changing libraries to SdFat.h the issue seems to be the SPI speed. With the SD card initialized the thermocouples are zero, with the single line commenetd out in the program that initializes the crad in the setup loop, they all read fine. The code is attached.

     

    So continuing to dig into the Adafruit_MAX31855.h library and I found that in Adafruit_MAX31855.h the function that triggers the thermcouples to readout is:

     

    uint32_t Adafruit_MAX31855::spiread32(void) {

      int i;

      uint32_t d = 0;

     

     

      digitalWrite(sclk, LOW);

      _delay_ms(1);

      digitalWrite(cs, LOW);

      _delay_ms(1);

     

     

      for (i=31; i>=0; i--)

      {

        digitalWrite(sclk, LOW);

        _delay_ms(1);

        d <<= 1;

        if (digitalRead(miso)) {

          d |= 1;

        }

     

     

        digitalWrite(sclk, HIGH);

        _delay_ms(1);

      }

     

     

      digitalWrite(cs, HIGH);

      Serial.println(d, HEX);

      return d;

    }

     

     

     

    The question is how do I change this function to interface with the SPI_HALF_SPEED or SPI_FULL_SPEED as utilized by the SdFat.h library?

     

    THANKS!

    Attachments:
    4-Channel TC Logger 2.21.13.txt.zip