Modifying code to run multiple MLX90333 sensors with Arduino Micro

Using Arduino Networking, Protocols, and Devices
#1

Hey guys, I am working on a project in which I need my Arduino Mirco to talk to and receive data from multiple MLX90333 Sensors. Below is my working code for sending and receiving data between one sensor and my arduino.

#include <SPI.h>
#include <stdint.h>

//*******Arduino MICRO SPI pins********
#define SS 17   //brown
#define SCK 15  //blue
#define MOSI 16  //SDI MOSI green
#define MISO 14  //SDO MISO yellow

byte dataBuffer[8];

void setup() {
  Serial.begin(9600); 
  SPI.begin;
  pinMode(SS, OUTPUT);
  pinMode(SCK, OUTPUT);
  pinMode(MOSI, OUTPUT);
  pinMode(MISO, INPUT);
}

void loop() {
  delay(20); //MLX90333 startup takes 16ms
  SPI.beginTransaction(SPISettings(160000, MSBFIRST, SPI_MODE1)); //320000 is about max
  delay(5);
  int j;
  for (j=0; j<10; j++){
    digitalWrite(SS, LOW);
    delay(20);  //Short delay necessary here
    int i;
    for (i=0; i<8; i++){ 
      dataBuffer[i] = SPI.transfer(255);  // Must transfer 1's, 0's don't work
      }
    digitalWrite(SS, HIGH);
    
    SPI.endTransaction();
    Serial.print(dataBuffer[2],8); //Print 3rd byte, MSB for Alpha
    Serial.print(" ,");
    Serial.print(dataBuffer[4],8); //Print 5th byte, MSB for Beta
    Serial.println(" ,");
    }
  }

The circuit I am using is the recommended Serial Protocol ckt schematic for the MLX90333 (8-soic packaging.) The link below has the MLX90333 data sheet; page 42 holds the schematic I used.

https://www.melexis.com/-/media/files/documents/.../mlx90333-datasheet-melexis.pdf

The method I have chose to connect multiple slave is pictured below.

I have tried to connecting two sensors using the same serial protocol in combination with the multiple slave select pin method I show above. Then I tried to modify my code to talk to both, but I was unable to get it to compile although I thought it seemed trivial after getting one sensor’s code to work.

So my questions are:

  1. Is there anything wrong with what I have so far?
  2. How do I modify my code to handle the multiple sensors?
  3. What pins can be used as Slave Select pins other than the already designated SS/ pin?

Any information, leads, or hand holding would be much appreciated!

Thanks!

#2

What is the point today showing your working code? You don't need help with that.

#3

That code only works with one sensors. How do I modify it to work with multiple sensors.

#4

Add more select lines.

#5

Which pins on arduino Micro can be slave select?

Do I have to define them differently in my code?

For example I have the designated slave select defined like:

#define SS 17

Would I define my next one, say pin 2 assuming it would work as a SS/, like:

#define SS1 2
#6

Yes, that would be one approach. You could then put those values in an array.

#7

So something like this?

//*******Arduino MICRO SPI pins********
#define SS 17   //brown
#define SCK 15  //blue
#define MOSI 16  //SDI MOSI green
#define MISO 14  //SDO MISO yellow
#define SS1 2

int SSPins[] = {17 2};

byte dataBuffer[8];

void setup() {
  Serial.begin(9600); 
  SPI.begin;
  pinMode(SSPins, OUTPUT);
  pinMode(SCK, OUTPUT);
  pinMode(MOSI, OUTPUT);
  pinMode(MISO, INPUT);
}

Notice the pin mode part especially, I am not sure if that would be the right way to set the mode of all those two pins.

#8

  pinMode(SSPins, OUTPUT);There is no overload of pinMode that accepts an array. You have to do each pin explicitly.

#9

Okay this is what I have so far:

#include <SPI.h>
#include <stdint.h>

//*******Arduino MICRO SPI pins********
#define SS 17   
#define SCK 15  
#define MOSI 16  
#define MISO 14  
#define SS1 2

byte dataBuffer[8];

void setup() {
  Serial.begin(9600); 
  SPI.begin;
  pinMode(SS, OUTPUT);
  pinMode(SCK, OUTPUT);
  pinMode(MOSI, OUTPUT);
  pinMode(MISO, INPUT);
  pinMode(SS1, OUTPUT);

 
}

void loop() {
  delay(20); //MLX90333 startup takes 16ms
  SPI.beginTransaction(SPISettings(160000, MSBFIRST, SPI_MODE1)); //320000 is about max
  delay(5);
  int j;
  
  for (j=0; j<10; j++){
    digitalWrite(SS, LOW);
    delay(20);  //Short delay necessary here
    int i;
    for (i=0; i<8; i++){ 
      dataBuffer[i] = SPI.transfer(255);  // Must transfer 1's, 0's don't work
      }
    digitalWrite(SS, HIGH);
    
    SPI.endTransaction();
    Serial.print(dataBuffer[2],8); //Print 3rd byte, MSB for Alpha
    Serial.print(" ,");
    Serial.print(dataBuffer[4],8); //Print 5th byte, MSB for Beta
    Serial.println(" ,");
    }

   for (j=0; j<10; j++){
    digitalWrite(SS1, LOW);
    delay(20);  //Short delay necessary here
    int i;
    for (i=0; i<8; i++){ 
      dataBuffer[i] = SPI.transfer(255);  // Must transfer 1's, 0's don't work
      }
    digitalWrite(SS1, HIGH);
    
    SPI.endTransaction();
    Serial.print(dataBuffer[2],8); //Print 3rd byte, MSB for Alpha
    Serial.print(" ,");
    Serial.print(dataBuffer[4],8); //Print 5th byte, MSB for Beta
    Serial.println(" ,");
    }
  }

I wasn’t sure how to use the array, although I can see where it may be useful. Until I understand how to use it, I’ll leave it out.

The code does compile and uploads, but when view the serial monitor it only shows two columns where I would like to get four (two for each sensor displaying the two angles of the magnetic field each of them senses.) Furthermore, I the readings I see are all zeroes accept when I make a really rapid movement over one of the sensor- then I see a very short few lines of non-zeros before it goes back to all zeros.

I looked walked through the code a couple times and everything seems like it should work… any suggestions?

#10

Why do you have these? Doesn't SPI.begin() take care of those for you?

#define SCK 15  
#define MOSI 16  
#define MISO 14

and

pinMode(SCK, OUTPUT);
  pinMode(MOSI, OUTPUT);
  pinMode(MISO, INPUT);
#11

I just tried my single sensor code with those lines commented out, and I found that you are correct that they are unneeded. My two sensor circuit still doesn’t work though. When using SPI.begin, I should still need to define additional Slave select pins right? Here is that chunk of code:

//*******Arduino MICRO SPI pins********
//#define SS 17   
//#define SCK 15  
//#define MOSI 16  
//#define MISO 14  
#define SS1 2

byte dataBuffer[8];

void setup() {
  Serial.begin(9600); 
  SPI.begin;
  //pinMode(SS, OUTPUT);
  //pinMode(SCK, OUTPUT);
  //pinMode(MOSI, OUTPUT);
  //pinMode(MISO, INPUT);
  pinMode(SS1, OUTPUT);

}
#12