MSP430FR4133 LaunchPad and MCP9808 sensor example using Energia

In this article we look at the MCP9808 digital temperature sensor and connect it to a MSP430FR4133 LaunchPad. We will have an example using the Energia IDE showing the sensor in action.

First a little bit of information regarding the sensor

The MCP9808 digital temperature sensor converts temperatures between -20°C and +100°C to a digital word with ±0.5°C (max.) accuracy. The MCP9808 comes with user-programmable registers that provide flexibility for temperature sensing applications.

The registers allow user-selectable settings such as Shutdown or low-power modes and the specification of temperature Event and Critical output boundaries. When the temperature changes beyond the specified boundary limits, the MCP9808 outputs an Event signal.

The user has the option of setting the event output signal polarity as an active-low or active-high comparator output for thermostat operation, or as temperature event interrupt output for microprocessor-based systems.

The event output can also be configured as a Critical temperature output. This sensor has an industry standard 2-wire, SMBus and Standard I2C™Compatible compatible (100kHz/400kHz bus clock) serial interface, allowing up to eight sensors to be controlled in a single serial bus.

Features

Accuracy:
±0.25°C (typical) from -40°C to +125°C
±0.5°C (maximum) from -20°C to +100°C

User Selectable Measurement Resolution:
0.5°C, 0.25°C, 0.125°C, 0.0625°C

User Programmable Temperature Limits:
Temperature Window Limit
Critical Temperature Limit

User Programmable Temperature Alert Output
Operating Voltage Range: 2.7V to 5.5V

More details about the sensor at http://www.microchip.com/wwwproducts/en/MCP9808

This typically comes in a breakout such as the one in the breakout below

Parts Required

Schematic/Connection

Here are the connectors on the launchpad

Code Example

[codesyntax lang=”cpp”]

#include<Wire.h>

// MCP9808 I2C address is 0x18(24)
#define Addr 0x18

void setup()
{
  // Initialise I2C communication as MASTER
  Wire.begin();
  // Initialise Serial Communication, set baud rate = 9600
  Serial.begin(9600);
  
  // Start I2C Transmission
  Wire.beginTransmission(Addr);
  // Select configuration register
  Wire.write(0x01);
  // Continuous conversion mode, Power-up default
  Wire.write(0x00);
  Wire.write(0x00);
  // Stop I2C Transmission
  Wire.endTransmission();
  
  // Start I2C Transmission
  Wire.beginTransmission(Addr);
  // Select resolution rgister
  Wire.write(0x08);
  // Resolution = +0.0625 / C
  Wire.write(0x03);
  // Stop I2C Transmission
  Wire.endTransmission();
}

void loop()
{
  unsigned int data[2];
  
  // Starts I2C communication
  Wire.beginTransmission(Addr);
  // Select data register
  Wire.write(0x05);
  // Stop I2C transmission
  Wire.endTransmission();
  
  // Request 2 bytes of data
  Wire.requestFrom(Addr, 2);
  
  // Read 2 bytes of data
  // temp MSB, temp LSB
  if(Wire.available() == 2)
  {
    data[0] = Wire.read();
    data[1] = Wire.read();
  }
  
  // Convert the data to 13-bits
  int temp = ((data[0] & 0x1F) * 256 + data[1]);
  if(temp > 4095)
  {
    temp -= 8192;
  }
  float cTemp = temp * 0.0625;
  float fTemp = cTemp * 1.8 + 32;
  
  // Output data to screen
  Serial.print("Temperature in Celsius : ");
  Serial.print(cTemp);
  Serial.println(" C");
  Serial.print("Temperature in Fahrenheit : ");
  Serial.print(fTemp);
  Serial.println(" F");
  delay(500);
}

[/codesyntax]

Results

Open the serial monitor and you should see something like this

Temperature in Celsius : 23.50 C
Temperature in Fahrenheit : 74.30 F
Temperature in Celsius : 23.50 C
Temperature in Fahrenheit : 74.30 F
Temperature in Celsius : 23.56 C
Temperature in Fahrenheit : 74.41 F
Temperature in Celsius : 23.50 C
Temperature in Fahrenheit : 74.30 F
Temperature in Celsius : 23.50 C
Temperature in Fahrenheit : 74.30 F