Trouble with MAX31855 Sensors and Ethernet Shield W5100 on Arduino mega 2560

Projects Programming
1

Hello,

I am working on a project where I connect 7 MAX31855 temperature sensors to and Arduino mega 2560. Everything works fine when I test it without the Ethernet Shield W5100, and I can see valid temperature readings on the Serial Monitor

However, when I stack the Ethernet Shield W5100 on the Arduino mega 2560 and connect an Ethernet cable, the temperature readings from all sensors show 0°C.

Code 1: Reading Temperatures from MAX31855 Sensors

This code works fine when run on the Arduino mega 2560 without the Ethernet shield. I am able to see valid temperature readings on the Serial Monitor.

#include <SPI.h>
#include <Adafruit_MAX31855.h>

// Define CS pins for each thermocouple
#define TC1_CS 28
#define TC2_CS 26
#define TC3_CS 24
#define TC4_CS 22
#define TC5_CS 30  // New CS pin for HT. Rücklauf wasser
#define TC6_CS 32  // New CS pin for VT. Rücklauf wasser
#define TC7_CS 34 

// Shared SPI Clock and MISO
#define MAX31855_CLK 52 
#define MAX31855_MISO 50 

// Create objects for each MAX31855 sensor
Adafruit_MAX31855 tc1(MAX31855_CLK, TC1_CS, MAX31855_MISO);
Adafruit_MAX31855 tc2(MAX31855_CLK, TC2_CS, MAX31855_MISO);
Adafruit_MAX31855 tc3(MAX31855_CLK, TC3_CS, MAX31855_MISO);
Adafruit_MAX31855 tc4(MAX31855_CLK, TC4_CS, MAX31855_MISO);
Adafruit_MAX31855 tc5(MAX31855_CLK, TC5_CS, MAX31855_MISO);  
Adafruit_MAX31855 tc6(MAX31855_CLK, TC6_CS, MAX31855_MISO);  
Adafruit_MAX31855 tc7(MAX31855_CLK, TC7_CS, MAX31855_MISO);  

void setup() {
  Serial.begin(9600);  // Start serial communication
  Serial.println("Initializing MAX31855 sensors...\n");

  // Check if all sensors are properly connected
  if (!tc1.begin()) Serial.println("Error: TC1 not detected!");
  if (!tc2.begin()) Serial.println("Error: TC2 not detected!");
  if (!tc3.begin()) Serial.println("Error: TC3 not detected!");
  if (!tc4.begin()) Serial.println("Error: TC4 not detected!");
  if (!tc5.begin()) Serial.println("Error: TC5 not detected!");  // Check for new sensor
  if (!tc6.begin()) Serial.println("Error: TC6 not detected!");  // Check for new sensor
  if (!tc7.begin()) Serial.println("Error: TC7 not detected!");  // Corrected error message
}

void loop() {
  // Read temperature from each thermocouple
  double temp1 = tc1.readCelsius();
  double temp2 = tc2.readCelsius();
  double temp3 = tc3.readCelsius();
  double temp4 = tc4.readCelsius();
  double temp5 = tc5.readCelsius();  // Read from new sensor
  double temp6 = tc6.readCelsius();  // Read from new sensor
  double temp7 = tc7.readCelsius();  // Read from the corrected sensor

  // Print temperature readings with labels beside values
  Serial.print("VT. Vorlauf (Heizgerät): ");
  if (isnan(temp1)) {
    Serial.println("Error");
  } else {
    Serial.print(temp1);
    Serial.println(" °C");
  }

  Serial.print("VT. Rücklauf (Heizgerät): ");
  if (isnan(temp2)) {
    Serial.println("Error");
  } else {
    Serial.print(temp2);
    Serial.println(" °C");
  }

  Serial.print("HT. Vorlauf (Heizgerät): ");
  if (isnan(temp3)) {
    Serial.println("Error");
  } else {
    Serial.print(temp3);
    Serial.println(" °C");
  }

  Serial.print("HT. Rücklauf (Heizgerät): ");
  if (isnan(temp4)) {
    Serial.println("Error");
  } else {
    Serial.print(temp4);
    Serial.println(" °C");
  }

  // Print readings for new thermocouples
  Serial.print("HT. Rücklauf Wasser: ");
  if (isnan(temp5)) {
    Serial.println("Error");
  } else {
    Serial.print(temp5);
    Serial.println(" °C");
  }

  Serial.print("VT. Rücklauf Wasser: ");
  if (isnan(temp6)) {
    Serial.println("Error");
  } else {
    Serial.print(temp6);
    Serial.println(" °C");
  }
  
  Serial.print("VT. Vorlauf Wasser: ");
  if (isnan(temp7)) {  // Fixed missing closing parenthesis here
    Serial.println("Error");
  } else {
    Serial.print(temp7);
    Serial.println(" °C");
  }

  // Separator for readability
  Serial.println("--------------------");

  delay(10000);  // Wait 10 seconds before the next reading
}

Code 2: Using Ethernet Shield W5100 and MQTT

This is the code where the Ethernet Shield W5100 is used along with MQTT. However, when I run this code, all the sensor readings return 0°C. I have tried connecting the Ethernet Shield with the sensors, but no valid temperature data is received.

#include <SPI.h>
#include <Ethernet.h>
#include <PubSubClient.h>
#include <Adafruit_MAX31855.h>

// Define CS pins for each thermocouple
#define TC1_CS 28
#define TC2_CS 26
#define TC3_CS 24
#define TC4_CS 22
#define TC5_CS 30  // New CS pin for HT. Rücklauf Wasser
#define TC6_CS 32  // New CS pin for VT. Rücklauf Wasser
#define TC7_CS 34  // VT. Vorlauf Wasser

// Shared SPI Clock and MISO
#define MAX31855_CLK 52 
#define MAX31855_MISO 50 

// Ethernet settings
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192, 168, 91, 00);
const char* mqtt_server = "192.168.91.222";  // Replace with your MQTT server IP
const int mqtt_port = 1883;
const char* mqtt_topic = "temp";

// Ethernet and MQTT client objects
EthernetClient ethClient;
PubSubClient client(ethClient);

// Create sensor objects
Adafruit_MAX31855 tc1(MAX31855_CLK, TC1_CS, MAX31855_MISO);
Adafruit_MAX31855 tc2(MAX31855_CLK, TC2_CS, MAX31855_MISO);
Adafruit_MAX31855 tc3(MAX31855_CLK, TC3_CS, MAX31855_MISO);
Adafruit_MAX31855 tc4(MAX31855_CLK, TC4_CS, MAX31855_MISO);
Adafruit_MAX31855 tc5(MAX31855_CLK, TC5_CS, MAX31855_MISO);
Adafruit_MAX31855 tc6(MAX31855_CLK, TC6_CS, MAX31855_MISO);
Adafruit_MAX31855 tc7(MAX31855_CLK, TC7_CS, MAX31855_MISO);

void setup() {
  Serial.begin(9600);
  Serial.println("Initializing MAX31855 sensors...\n");

  // Initialize Ethernet
  Ethernet.begin(mac, ip);
  delay(1000);
  Serial.println("Ethernet initialized");

  // Initialize MQTT
  client.setServer(mqtt_server, mqtt_port);
  while (!client.connected()) {
    Serial.print("Connecting to MQTT broker...");
    if (client.connect("ArduinoClient")) {
      Serial.println("Connected");
    } else {
      Serial.print("Failed to connect, rc=");
      Serial.print(client.state());
      delay(2000);
    }
  }

  // Check if all sensors are properly connected
  checkSensor(tc1, TC1_CS, "VT. Vorlauf (Heizgerät)");
  checkSensor(tc2, TC2_CS, "VT. Rücklauf (Heizgerät)");
  checkSensor(tc3, TC3_CS, "HT. Vorlauf (Heizgerät)");
  checkSensor(tc4, TC4_CS, "HT. Rücklauf (Heizgerät)");
  checkSensor(tc5, TC5_CS, "HT. Rücklauf Wasser");
  checkSensor(tc6, TC6_CS, "VT. Rücklauf Wasser");
  checkSensor(tc7, TC7_CS, "VT. Vorlauf Wasser");

  Serial.println("Initialization Complete!\n");
}

void loop() {
  // Check MQTT connection
  if (!client.connected()) {
    while (!client.connected()) {
      Serial.print("Connecting to MQTT broker...");
      if (client.connect("ArduinoClient")) {
        Serial.println("Connected");
      } else {
        Serial.print("Failed to connect, rc=");
        Serial.print(client.state());
        delay(2000);
      }
    }
  }

  // Read temperature from each thermocouple
  double temp1 = tc1.readCelsius();
  double temp2 = tc2.readCelsius();
  double temp3 = tc3.readCelsius();
  double temp4 = tc4.readCelsius();
  double temp5 = tc5.readCelsius();
  double temp6 = tc6.readCelsius();
  double temp7 = tc7.readCelsius();

  // Create MQTT message
  String message = "";
  message += "VT. Vorlauf (Heizgerät): " + checkForErrors(tc1, temp1) + " °C, ";
  message += "VT. Rücklauf (Heizgerät): " + checkForErrors(tc2, temp2) + " °C, ";
  message += "HT. Vorlauf (Heizgerät): " + checkForErrors(tc3, temp3) + " °C, ";
  message += "HT. Rücklauf (Heizgerät): " + checkForErrors(tc4, temp4) + " °C, ";
  message += "HT. Rücklauf Wasser: " + checkForErrors(tc5, temp5) + " °C, ";
  message += "VT. Rücklauf Wasser: " + checkForErrors(tc6, temp6) + " °C, ";
  message += "VT. Vorlauf Wasser: " + checkForErrors(tc7, temp7) + " °C";

  // Publish the temperature readings to MQTT topic
  client.publish(mqtt_topic, message.c_str());
  Serial.println("Message sent: " + message);

  // Wait before the next reading
  delay(10000);
}

void checkSensor(Adafruit_MAX31855 &sensor, int csPin, String name) {
  digitalWrite(csPin, LOW);
  delay(10);
  if (!sensor.begin()) {
    Serial.println("Error: " + name + " not detected!");

could some one guide . thanks a lot .

2

It should really come as no surprise that using software SPI on the hardware SPI pins for your sensors conflicts with using hardware SPI for your ethernet shield on the same pins.

1 Like
3

Hi thanks for answer

// Create sensor objects using **hardware SPI**
Adafruit_MAX31855 tc1(TC1_CS);
Adafruit_MAX31855 tc2(TC2_CS);
Adafruit_MAX31855 tc3(TC3_CS);
Adafruit_MAX31855 tc4(TC4_CS);
Adafruit_MAX31855 tc5(TC5_CS);
Adafruit_MAX31855 tc6(TC6_CS);
Adafruit_MAX31855 tc7(TC7_CS);

I have to do this way .

#define MAX31855_CLK 52 
#define MAX31855_MISO 50

And have to remove this ?

Thanks

4

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