Issues using multiple BME280 sensors over SPI

[bschlach]

Hello. I am currently working on a project using an Arduino Mega (ATmega2560) with BME280 sensors to collect temperature, humidity, and pressure. I am also using an RS232 to TTL converter to collect lab scale data, and the ethernet shield 2 for to display live data and save to an SD card.

The issue I am having is using multiple BME280 sensors over SPI. I am opting for SPI for the longer cable length, and I am currently using 8-pin M12 cables to transfer the data. I would ideally like to use four BME280 sensors simultaneously, however I get erratic readings when using more than one. Depening on the number of sensors attached, I get anywhere from 20 degrees to 140 degrees off from the readings. The cable lengths are roughly 1m each, with about 0.25 M of wires coming from the M12 receptacles mounted on my enclosure to a solder board.

I have been able to get multiple BME sensors working with longer M12 cable lengths before, but I believe the issues are arising from the ethernet shield since it also uses SPI for communication. The issue applies even when I use the example sketch for the BME sensors below:

#include <Wire.h>
#include <SPI.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>

#define BME_SCK 7
#define BME_MISO 6
#define BME_MOSI 5
#define BME_CS 4
#define BME_CS2 3
#define BME_CS3 2
#define BME_CS4 1

#define SEALEVELPRESSURE_HPA (1013.25)

//Adafruit_BME280 bme; // I2C
//Adafruit_BME280 bme(BME_CS); // hardware SPI
Adafruit_BME280 bme(BME_CS, BME_MOSI, BME_MISO, BME_SCK);    // software SPI
Adafruit_BME280 bme2(BME_CS2, BME_MOSI, BME_MISO, BME_SCK);  // software SPI
Adafruit_BME280 bme3(BME_CS3, BME_MOSI, BME_MISO, BME_SCK);  // software SPI
Adafruit_BME280 bme4(BME_CS4, BME_MOSI, BME_MISO, BME_SCK);  // software SPI

unsigned long delayTime;

void setup() {
  Serial.begin(9600);
  while (!Serial)
    ;  // time to get serial running
  Serial.println(F("BME280 test"));
  unsigned status;
  unsigned status2;
  unsigned status3;
  unsigned status4;

  // default settings
  status = bme.begin();
  status2 = bme2.begin();
  status3 = bme3.begin();
  status4 = bme4.begin();
  
  // You can also pass in a Wire library object like &Wire2
  // status = bme.begin(0x76, &Wire2)
  if (!status) {
    Serial.println("Could not find a valid BME280 sensor, check wiring, address, sensor ID!");
    Serial.print("SensorID was: 0x");
    Serial.println(bme.sensorID(), 16);
    Serial.print("        ID of 0xFF probably means a bad address, a BMP 180 or BMP 085\n");
    Serial.print("   ID of 0x56-0x58 represents a BMP 280,\n");
    Serial.print("        ID of 0x60 represents a BME 280.\n");
    Serial.print("        ID of 0x61 represents a BME 680.\n");
    while (1) delay(10);
  }

  Serial.println("-- Default Test --");
  delayTime = 8000;

  Serial.println();
}


void loop() {
  printValues();
  delay(delayTime);
}


void printValues() {
  Serial.print("Temperature = ");
  Serial.print(bme.readTemperature());
  Serial.println(" °C");

  Serial.print("Temperature 2 = ");
  Serial.print(bme2.readTemperature());
  Serial.println(" °C");

  Serial.print("Temperature 3 = ");
  Serial.print(bme3.readTemperature());
  Serial.println(" °C");

  Serial.print("Temperature 4 = ");
  Serial.print(bme4.readTemperature());
  Serial.println(" °C");
  Serial.print("Pressure = ");

  Serial.print(bme.readPressure() / 100.0F);
  Serial.println(" hPa");

  Serial.print("Pressure 2 = ");

  Serial.print(bme2.readPressure() / 100.0F);
  Serial.println(" hPa");


  Serial.print("Humidity = ");
  Serial.print(bme.readHumidity());
  Serial.println(" %");

  Serial.print("Humidity 2 = ");
  Serial.print(bme2.readHumidity());
  Serial.println(" %");

  Serial.print("Humidity 3 = ");
  Serial.print(bme3.readHumidity());
  Serial.println(" %");
  Serial.println();

  Serial.print("Humidity 4 = ");
  Serial.print(bme4.readHumidity());
  Serial.println(" %");
  
}

I have not included images of the breadboard since there are several other components on it and it will be unhelpful in determining the issue. All 4 ports work on their own, but the issue only arises when multiple sensors are connected.

Any help or direction would be very appreciated.