How to Use Adafruit Thermocouple Amplifier with 1-Wire Breakout Board - MAX31850K: Examples, Pinouts, and Specs

The Adafruit Thermocouple Amplifier with 1-Wire Breakout Board featuring the MAX31850K is a sophisticated electronic component designed to amplify the tiny voltage from a thermocouple to a more easily measurable level. It also digitizes the signal and communicates over a 1-Wire interface. This breakout board is commonly used in applications requiring precise temperature measurements, such as industrial systems, home brewing, and HVAC systems.

• Supply Voltage (VDD): 3.0V to 3.6V
• Operating Current: 1.5mA (typical)
• Temperature Resolution: 0.25°C (max)
• Temperature Accuracy: ±2°C (max)
• Temperature Range (Thermocouple): -200°C to +700°C
• Interface: 1-Wire
• Package: SOIC-8 surface mount

1. Power Supply: Connect the VDD pin to a 3.0V to 3.6V power source and the GND pin to the ground.
2. Thermocouple Connection: Attach the thermocouple leads to the T+ and T- pins, ensuring correct polarity.
3. Data Communication: Connect the DQ pin to a digital I/O pin on your microcontroller capable of 1-Wire communication.
4. Pull-up Resistor: Attach a 4.7kΩ pull-up resistor between the DQ pin and VDD to ensure proper 1-Wire signal levels.

• Ensure that the power supply is within the specified voltage range to prevent damage.
• Use twisted pair wires for the thermocouple to minimize electrical noise and improve measurement accuracy.
• Keep the breakout board away from heat sources other than the thermocouple to avoid false readings.
• Use proper ESD precautions when handling the breakout board to prevent damage to the sensitive electronics.

• Inaccurate Temperature Readings: Ensure that the thermocouple is properly connected with the correct polarity and that there are no loose connections.
• No Data on 1-Wire Bus: Check the pull-up resistor on the DQ line and ensure that the microcontroller is correctly configured for 1-Wire communication.

• If you encounter noise in the temperature readings, consider using a filter capacitor across the power supply pins or increasing the distance between the thermocouple wires and other electronic devices.
• For issues with the 1-Wire communication, verify that only one device is trying to communicate on the bus at a time, as the 1-Wire protocol is half-duplex.

Q: Can I use this breakout board with any microcontroller? A: Yes, as long as the microcontroller supports 1-Wire communication and operates within the voltage range of the MAX31850K.

Q: How long can the thermocouple wires be? A: Thermocouple wires can be extended; however, the longer the wires, the more susceptible the system is to noise. Use twisted pair wires and keep the length reasonable.

Q: Is calibration necessary for accurate readings? A: The MAX31850K is factory-calibrated, but for critical applications, you may want to perform additional calibration to account for system-level inaccuracies.

#include <OneWire.h>

// OneWire DS18S20, DS18B20, DS1822 Temperature Example
//
// http://www.pjrc.com/teensy/td_libs_OneWire.html

OneWire  ds(10);  // on pin 10 (a 4.7K resistor is necessary)

void setup(void) {
  Serial.begin(9600);
}

void loop(void) {
  byte i;
  byte present = 0;
  byte type_s;
  byte data[12];
  byte addr[8];
  float celsius, fahrenheit;
  
  if ( !ds.search(addr)) {
    Serial.println("No more addresses.");
    Serial.println();
    ds.reset_search();
    delay(250);
    return;
  }
  
  if (OneWire::crc8(addr, 7) != addr[7]) {
      Serial.println("CRC is not valid!");
      return;
  }
  Serial.println();

  // Match the address to the MAX31850K
  if (addr[0] == 0x3B) {
    type_s = 1;
  } else {
    Serial.println("Device is not a MAX31850K.");
    return;
  } 

  ds.reset();
  ds.select(addr);
  ds.write(0x44, 1);        // start conversion, with parasite power on at the end
  
  delay(1000);     // maybe 750ms is enough, maybe not
  // we might do a ds.depower() here, but the reset will take care of it.
  
  present = ds.reset();
  ds.select(addr);    
  ds.write(0xBE);         // Read Scratchpad

  for ( i = 0; i < 9; i++) {           // we need 9 bytes
    data[i] = ds.read();
  }
  
  // Convert the data to actual temperature
  // because the result is a 16 bit signed integer, it should
  // be stored to an "int16_t" type, which is always 16 bits
  // even when compiled on a 32 bit processor.
  int16_t raw = (data[1] << 8) | data[0];
  if (type_s) {
    raw = raw << 3; // 9 bit resolution default
    if (data[7] == 0x10) {
      // "count remain" gives full 12 bit resolution
      raw = (raw & 0xFFF0) + 12 - data[6];
    }
  } else {
    byte cfg = (data[4] & 0x60);
    // at lower res, the low bits are undefined, so let's zero them
    if (cfg == 0x00) raw = raw & ~7;  // 9 bit resolution, 93.75 ms
    else if (cfg == 0x20) raw = raw & ~3; // 10 bit res, 187.5 ms
    else if (cfg == 0x40) raw = raw & ~1; // 11 bit res, 375 ms
    //// default is 12 bit resolution, 750 ms conversion time
  }
  celsius = (float)raw / 16.0;
  fahrenheit = celsius * 1.8 + 32.0;
  Serial.print("  Temperature = ");
  Serial.print(celsius);
  Serial.print(" Celsius, ");
  Serial.print(fahrenheit);
  Serial.println(" Fahrenheit");
}

Note: This example code is for illustration purposes and may require modifications to work with the MAX31850K. Ensure that the correct device address is used and that the microcontroller's digital I/O pin matches the one defined in the code (OneWire ds(10); corresponds to pin 10 on the Arduino UNO).