Connecting more SPI devices

Other Hardware Sensors
1

Hello,
I'm newbie in Arduino.
I want to make a controller for an industrial oven and I want to read 6 PT100 sensors.
I'm using a chineese version of max31865 to connect them to Arduino Mega.
I wire up 1 sensor first, it works.
I add 1 more, it works.
When I added the 4th, all the sensors are giving under/overvoltage error.

I used the demo sketch for max31865 as follows:

/*************************************************** 
  This is a library for the Adafruit PT100/P1000 RTD Sensor w/MAX31865

  Designed specifically to work with the Adafruit RTD Sensor
  ----> https://www.adafruit.com/products/3328

  This sensor uses SPI to communicate, 4 pins are required to  
  interface
  Adafruit invests time and resources providing this open source code, 
  please support Adafruit and open-source hardware by purchasing 
  products from Adafru  it!

  Written by Limor Fried/Ladyada for Adafruit Industries.  
  BSD license, all text above must be included in any redistribution
 ****************************************************/

#include <Adafruit_MAX31865.h>

// Use software SPI: CS, DI, DO, CLK
//Adafruit_MAX31865 thermo = Adafruit_MAX31865(10, 11, 12, 13);
// use hardware SPI, just pass in the CS pin
Adafruit_MAX31865 thermo53 = Adafruit_MAX31865(53);
Adafruit_MAX31865 thermo49 = Adafruit_MAX31865(49);
Adafruit_MAX31865 thermo48 = Adafruit_MAX31865(48);
Adafruit_MAX31865 thermo47 = Adafruit_MAX31865(47);

// The value of the Rref resistor. Use 430.0 for PT100 and 4300.0 for PT1000
#define RREF      430.0
// The 'nominal' 0-degrees-C resistance of the sensor
// 100.0 for PT100, 1000.0 for PT1000
#define RNOMINAL  100.0

void setup() {
  Serial.begin(115200);
  Serial.println("Adafruit MAX31865 PT100 Sensor Test!");

  thermo53.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
  thermo49.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
  thermo48.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
  thermo47.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
}


void loop() {
  uint16_t rtd53 = thermo53.readRTD();

  /*Serial.print("RTD value: "); Serial.println(rtd);
  float ratio = rtd;
  ratio /= 32768;
  Serial.print("Ratio = "); Serial.println(ratio,8);
  Serial.print("Resistance = "); Serial.println(RREF*ratio,8);*/
  Serial.print("Temperature 53 = "); Serial.println(thermo53.temperature(RNOMINAL, RREF));
  delay(900);
  Serial.print("Temperature 49 = "); Serial.println(thermo49.temperature(RNOMINAL, RREF));
  delay(900);
  Serial.print("Temperature 48 = "); Serial.println(thermo48.temperature(RNOMINAL, RREF));
  delay(900);
  Serial.print("Temperature 47 = "); Serial.println(thermo47.temperature(RNOMINAL, RREF));
  delay(900);
  /*
  // Check and print any faults
  uint8_t fault = thermo.readFault();
  if (fault) {
    Serial.print("Fault 0x"); Serial.println(fault, HEX);
    if (fault & MAX31865_FAULT_HIGHTHRESH) {
      Serial.println("RTD High Threshold"); 
    }
    if (fault & MAX31865_FAULT_LOWTHRESH) {
      Serial.println("RTD Low Threshold"); 
    }
    if (fault & MAX31865_FAULT_REFINLOW) {
      Serial.println("REFIN- > 0.85 x Bias"); 
    }
    if (fault & MAX31865_FAULT_REFINHIGH) {
      Serial.println("REFIN- < 0.85 x Bias - FORCE- open"); 
    }
    if (fault & MAX31865_FAULT_RTDINLOW) {
      Serial.println("RTDIN- < 0.85 x Bias - FORCE- open"); 
    }
    if (fault & MAX31865_FAULT_OVUV) {
      Serial.println("Under/Over voltage"); 
    }
    thermo.clearFault();
  }*/
  Serial.println();
  delay(1000);
}

I followed this diagram for wiring:

http://www.learningaboutelectronics.com/images/SPI-hardware-configuration.png

What am I missing?

By the way, I read that on Mega the the ICSP connector can be used instead of ports 50-52 for SPI communication, but my ports (50-52) are not free using this sketch. I would prefer to use ports 50-52 to other purposes.
The library that I'm using is not configured correctly to free up ports 50-52?

thanks in advance

2

More power.

3

try this

 `/*************4 channel PT100's********************/

#include <Adafruit_MAX31865.h>
# include "SPI.h"       //********added************

// use hardware SPI, just pass in the CS pin
Adafruit_MAX31865 thermo53 = Adafruit_MAX31865(53);
Adafruit_MAX31865 thermo49 = Adafruit_MAX31865(49);
Adafruit_MAX31865 thermo48 = Adafruit_MAX31865(48);
Adafruit_MAX31865 thermo47 = Adafruit_MAX31865(47);

// The value of the Rref resistor. Use 430.0 for PT100 and 4300.0 for PT1000
#define RREF      430.0
#define RNOMINAL  100.0

void setup() {
  Serial.begin(115200);
  Serial.println("Adafruit MAX31865 PT100 Sensor Test!");

  thermo53.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
  thermo49.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
  thermo48.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
  thermo47.begin(MAX31865_3WIRE);  // set to 2WIRE or 4WIRE as necessary
}

void loop()
{
  uint16_t rtd53 = thermo53.readRTD();
  uint16_t rtd49 = thermo49.readRTD();    //********added************
  uint16_t rtd48 = thermo48.readRTD();    //********added************
  uint16_t rtd47 = thermo47.readRTD();    //********added************

  Serial.print("Temperature 53 = "); Serial.println(thermo53.temperature(RNOMINAL, RREF));
  delay(900);
  Serial.print("Temperature 49 = "); Serial.println(thermo49.temperature(RNOMINAL, RREF));
  delay(900);
  Serial.print("Temperature 48 = "); Serial.println(thermo48.temperature(RNOMINAL, RREF));
  delay(900);
  Serial.print("Temperature 47 = "); Serial.println(thermo47.temperature(RNOMINAL, RREF));
  delay(900);
  Serial.println();
  delay(1000);
}`
4

I thought that command is only for reading the RTD ratio, it has no relevance in reading temperature value.

5

Your version is ONLY measuring the RTD on pin53!

did you NOT try my version?

6

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