Project 9.02 Doing Something Based on Temperature

In this project we will use the temperature data to change the color of the Neopixels based on the temperature. The warmer the temperature to more red the Neopixels will appear. The colder the temperature sensor the more blue the Neopixels will appear.

Project Code:

//////////////////////////////////////////////////////
// 9.02 - Doing Something Based on Temperature

#include <Adafruit_NeoPixel.h>

byte dataPin = 10;     
byte numberOfPixels = 2;  
byte brightness = 10;     

byte redValue = 0;      
byte greenValue = 0;
byte blueValue = 0;     

byte tempSensorPin = A3;

Adafruit_NeoPixel pixels(numberOfPixels, dataPin, NEO_GRB + NEO_KHZ800);
void setup() {
  pinMode(tempSensorPin, INPUT);

  pixels.begin();
  pixels.setBrightness(brightness);

  Serial.begin(9600);
}

void loop() {

  float currentTemperature = ReadTemperature();

  Serial.print("The temp in C is: "); Serial.println(currentTemperature);
  Serial.print("The temp in F is: "); Serial.println(CtoF(currentTemperature));

  UpdatePixelColorBasedOnTemp(CtoF(currentTemperature));
  delay(1000);

}

/*
   This function takes a temperature in degrees F and updates the neopixels to reflect the temperature.
   The hotter the temperature, the more red the neopixels.
   The colder the temperature, the more blue the neopixels.
*/
void UpdatePixelColorBasedOnTemp(float temperature) {
 
  int blueValue = map(temperature, 70, 80, 255, 0);
  blueValue = constrain(blueValue, 0, 255);
  
  int redValue = map(temperature, 70, 80, 0, 255);
  redValue = constrain(redValue, 0, 255);

  Serial.print("Blue: "); Serial.println(blueValue);
  Serial.print("Red: "); Serial.println(redValue);

  pixels.setPixelColor(0, pixels.Color(redValue, 0, blueValue));
  pixels.setPixelColor(1, pixels.Color(redValue, 0, blueValue));
  pixels.show();
}

/*
   This function reads a temperature in degrees C from the MCP9700AT-E/TT and returns it.
*/
float ReadTemperature() {
  int currentTempReading = analogRead(tempSensorPin);

  float currentTempVoltage = currentTempReading * (5.0 / 1024.0); 
  float temperature = (currentTempVoltage - .5) /  .01;         

  return (temperature);
}

/*
   This function converts a temperature passed in degrees C to degrees F and returns it.
*/
float CtoF(float temp) {
  return ((temp * 1.8) + 32);
}
//////////////////////////////////////////////////////

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*If you’re copying and pasting the code, or typing from scratch, delete everything out of a new Arduino sketch and paste / type in the above text.

This project is fairly simple thanks to the functions we wrote in the last project. They are simply copied and pasted into this one.

The first thing that we need to do is include the Neopixel library.

#include <Adafruit_NeoPixel.h>

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Next, we declare some standard variables and include the constructor for the Neopixel library.

byte dataPin = 10;       
byte numberOfPixels = 2;  
byte brightness = 10;     

byte redValue = 0;      
byte greenValue = 0;
byte blueValue = 0;     

byte tempSensorPin = A3;

Adafruit_NeoPixel pixels(numberOfPixels, dataPin, NEO_GRB + NEO_KHZ800);

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After that in the setup() function, we set the pinMode of the analog pin connected to the temperature sensor, initialize the Neopixels, and setup Serial communication.

void setup() {
  pinMode(tempSensorPin, INPUT);

  pixels.begin();
  pixels.setBrightness(brightness);

  Serial.begin(9600);
}

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The loop() function starts just like the last project did. First, we get the current temperature.

void loop() {

  float currentTemperature = ReadTemperature();

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Next, the temperature is printed out in Celsius and Fahrenheit.

Serial.print("The temp in C is: "); Serial.println(currentTemperature);
Serial.print("The temp in F is: "); Serial.println(CtoF(currentTemperature));

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Let’s take a look at the next function in the loop(), “UpdatePixelColorBasedOnTemp”. From the function description we know that this function takes a temperature in degrees Fahrenheit and updates the Neopixels to reflect that temperature. This is why the temperature is passed to the function with the CtoF function.

UpdatePixelColorBasedOnTemp(CtoF(currentTemperature));

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Inside the function we can see what is really happening. First the blue value is mapped to the temperature range of 70 – 80 degrees F.

The parameters in this implementation of the map function are a bit different than usual. You’ll see that the higher end of the output range is mapped to the lower end of the temperature range, and vice versa. This means that when the temperature is 70 degrees the output will be 255 and when the temperature is 80 degrees the output will be 0. This is an easy way to invert the output range to go from high to low. We need this because as the temperature gets lower, we want a larger blue value.

int blueValue = map(temperature, 70, 80, 255, 0);

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Then the constrain function is used to ensure we stay in the proper output range.

blueValue = constrain(blueValue, 0, 255);

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Next, we will use the map function normally to map the temperature range to the red output range. The constrain function is used to keep the values in the proper range.

int redValue = map(temperature, 70, 80, 0, 255);
redValue = constrain(redValue, 0, 255);

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Then these values are printed out onto the Serial port.

Serial.print("Blue: "); Serial.println(blueValue);
Serial.print("Red: "); Serial.println(redValue);

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After that the Neopixels are loaded and updated.

  pixels.setPixelColor(0, pixels.Color(redValue, 0, blueValue));
  pixels.setPixelColor(1, pixels.Color(redValue, 0, blueValue));
  pixels.show();
}

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Going back to the loop() funciton, after the UpdatePixelColorBasedOnTemp function, a small delay is implemented to keep the Serial port from flooding and the loop() is ended.

  delay(1000);

}

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