ESP8266 & Pressure sensor MC5540 over SPI

virouf · June 7, 2022, 5:38am

Hello,

I'm trying to adapt the following code to my WeMos D1 R1 board, based on esp8266, to get a proper temperature & pressure from a MS5540 sensor : water-depth-using-ms5540c.

As of now, code seems to work, but it's probably only luck ... !

i'm geeting values for word1 to word4

word1 : 47942 - 1011101101000110
word2 : 63066 - 1111011001011010
word3 : 41184 - 1010000011100000
word4 : 48901 - 1011111100000101

the calibration coefficients are properly calculated, I checked versus the MS5540 datasheet.

c1 : 23971 - 101110110100011
c2 : 2053 - 100000000101
c3 : 764 - 1011111100
c4 : 643 - 1010000011
c5 : 985 - 1111011001
c6 : 26 - 11010

but the values D1 & D2 are wrong, always same value 65535, thus at the end the pressure and temperature displayed are incorrect.

D1 : 65535 - 1111111111111111
D2 : 65535 - 1111111111111111
Temp °C : 297 - 100101001
Pressure mBar : 2775 - 101011010111

My questions are the following:

ESP8266 is running at 80Mhz versus 16Mhz for the Arduino. In the original code there is a
SPI.setClockDivider(SPI_CLOCK_DIV32) that I tryed to adapt with /128 to be as close as possible to the 500Khz from the MS5540. Does it mean the controller and the sensor are not compatible on this point?
Orignal code have the instruction at the beginning of the loop TCCR1B = (TCCR1B & 0xF8) | 1 ; //generates the MCKL signal. Or course it doesn't work on esp8266 as registry TCCR1B doesn't exist for my µC, but as I don't really understand the purpose of it I'm in trouble to find a workaround for esp8266... But i assume this is driving the timing of the reading of the SPI? Thus probably the root cause of my issue.
finally, in the Reset Sequence figure (bottom, page 13) in the datasheet I understand the reset should be done with 3 bytes like this 10101010 1010101000 00000000 and not with 0x15 0x55 0x40 (00010101 01010101 01000000) as it's done in the code. What do I miss?

void resetsensor() //this function keeps the sketch a little shorter
{
  SPI.setDataMode(SPI_MODE0); 
  SPI.transfer(0x15);
  SPI.transfer(0x55);
  SPI.transfer(0x40);
}

My current code is below:

#include <SPI.h>

int pin_clock = 3;

void resetsensor() { //this function keeps the sketch a little shorter
  SPI.setDataMode(SPI_MODE0);
  SPI.transfer(0x15); //21
  SPI.transfer(0x55); //85
  SPI.transfer(0x40); //64
}

void setup(void) {
  Serial.begin(9600);
  
  SPI.begin(); //see SPI library details on arduino.cc for details
  SPI.setBitOrder(MSBFIRST);
  SPI.setClockDivider(SPI_CLOCK_DIV128); 
  
  pinMode(pin_clock, OUTPUT);
  delay(100);
}

void printValue(unsigned int wordX, const char* wordName){
  Serial.print(wordName);
  Serial.print(" : ");
  Serial.print(wordX);
  Serial.print(" - ");
  Serial.println(wordX,BIN);  
}

void loop(void) {
  
  //TCCR1B = (TCCR1B & 0xF8) | 1 ; //generates the MCKL signal
  analogWrite (pin_clock, 128) ;
  resetsensor();//resets the sensor - caution: afterwards mode = SPI_MODE0!

  
  //Calibration word 1
  unsigned int word1 = 0;
  unsigned int word11 = 0;
  SPI.transfer(0x1D); //29 send first byte of command to get calibration word 1
  SPI.transfer(0x50); //80 send second byte of command to get calibration word 1
  SPI.setDataMode(SPI_MODE1); //change mode in order to listen
  word1 = SPI.transfer(0x00); //send dummy byte to read first byte of word
  word1 = word1 << 8; //shift returned byte
  word11 = SPI.transfer(0x00); //send dummy byte to read second byte of word
  word1 = word1 | word11; //combine first and second byte of word
  printValue(word1, "word1");
  resetsensor();//resets the sensor

  //Calibration word 2; see comments on calibration word 1
  unsigned int word2 = 0;
  byte word22 = 0;
  SPI.transfer(0x1D);
  SPI.transfer(0x60); //96
  SPI.setDataMode(SPI_MODE1);
  word2 = SPI.transfer(0x00);
  word2 = word2 << 8;
  word22 = SPI.transfer(0x00);
  word2 = word2 | word22;
  printValue(word2, "word2");
  resetsensor();//resets the sensor

  //Calibration word 3; see comments on calibration word 1
  unsigned int word3 = 0;
  byte word33 = 0;
  SPI.transfer(0x1D);
  SPI.transfer(0x90); //144
  SPI.setDataMode(SPI_MODE1);
  word3 = SPI.transfer(0x00);
  word3 = word3 << 8;
  word33 = SPI.transfer(0x00);
  word3 = word3 | word33;
  printValue(word3, "word3");
  resetsensor();//resets the sensor

  //Calibration word 4; see comments on calibration word 1
  unsigned int word4 = 0;
  byte word44 = 0;
  SPI.transfer(0x1D);
  SPI.transfer(0xA0); //160
  SPI.setDataMode(SPI_MODE1);
  word4 = SPI.transfer(0x00);
  word4 = word4 << 8;
  word44 = SPI.transfer(0x00);
  word4 = word4 | word44;
  printValue(word4, "word4");

  long c1 = (word1 >> 1) & 0x7FFF;
  long c2 = ((word3 & 0x003F) << 6) | (word4 & 0x003F);
  long c3 = (word4 >> 6) & 0x03FF;
  long c4 = (word3 >> 6) & 0x03FF;
  long c5 = ((word1 & 0x0001) << 10) | ((word2 >> 6) & 0x03FF);
  long c6 = word2 & 0x003F;

  printValue(c1, "c1");
  printValue(c2, "c2");
  printValue(c3, "c3");
  printValue(c4, "c4");
  printValue(c5, "c5");
  printValue(c6, "c6");    
  
  resetsensor();//resets the sensor

  //Pressure:
  unsigned int presMSB = 0; //first byte of value
  unsigned int presLSB = 0; //last byte of value
  unsigned int D1 = 0;
  SPI.transfer(0x0F); //send first byte of command to get pressure value
  SPI.transfer(0x40); //send second byte of command to get pressure value
  delay(35); //wait for conversion end
  SPI.setDataMode(SPI_MODE1); //change mode in order to listen
  presMSB = SPI.transfer(0x00); //send dummy byte to read first byte of value
  presMSB = presMSB << 8; //shift first byte
  presLSB = SPI.transfer(0x00); //send dummy byte to read second byte of value
  D1 = presMSB | presLSB;
  printValue(D1,"D1");
  resetsensor();//resets the sensor
  
  //Temperature:
  unsigned int tempMSB = 0; //first byte of value
  unsigned int tempLSB = 0; //last byte of value
  unsigned int D2 = 0;
  SPI.transfer(0x0F); //send first byte of command to get temperature value
  SPI.transfer(0x20); //send second byte of command to get temperature value
  delay(35); //wait for conversion end
  SPI.setDataMode(SPI_MODE1); //change mode in order to listen
  tempMSB = SPI.transfer(0x00); //send dummy byte to read first byte of value
  tempMSB = tempMSB << 8; //shift first byte
  tempLSB = SPI.transfer(0x00); //send dummy byte to read second byte of value
  D2 = tempMSB | tempLSB; //combine first and second byte of value
  printValue(D2,"D2");
  resetsensor();//resets the sensor




  //calculation of the real values by means of the calibration factors and the maths
  //in the datasheet. const MUST be long
  const long UT1 = (c5 * 8) + 20224;
  const long dT = D2 - UT1;
  const long TEMP = 200 + ((dT * (c6 + 50)) >> 10);
  const long OFF  = (c2 * 4) + (((c4 - 512) * dT) >> 12);
  const long SENS = c1 + ((c3 * dT) >> 10) + 24576;
  const long X = (SENS * (D1 - 7168) >> 14) - OFF;
  long PCOMP = ((X * 10) >> 5) + 2500;
  float TEMPREAL = TEMP/10;
  float PCOMPHG = PCOMP * 750.06 / 10000; // mbar*10 -> mmHg === ((mbar/10)/1000)*750/06
  
  printValue(UT1,"UT1");
  printValue(dT,"dT");
  printValue(TEMP,"TEMP");
  printValue(OFF,"OFF");
  printValue(SENS,"SENS");
  printValue(X,"X");

  printValue(TEMPREAL,"Temp °C");
  printValue(PCOMP,"Pressure mBar");
  printValue(PCOMPHG,"Pressure mmHg");
  
  Serial.println("************************************");

  delay(1000);
}

Any hint are welcome, many thanks for the time you took for reading this post already.

Thanks,
V

system · December 4, 2022, 5:38am

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ESP8266 & Pressure sensor MC5540 over SPI

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