IOT Team 28: John Ranshaw, Christopher Ames

Published April 18, 2019 © GPL3+

Temperature and Humidity Sensor Controlling Humidifier

The use of a simple circuit and a DHT11 sensor to read the temperature and humidity. Allowing for the automated control of a humidifier.

IntermediateFull instructions provided7 hours2,025

Temperature and Humidity Sensor Controlling Humidifier

Things used in this project

Hardware components

Particle Photon

DHT11 Temperature & Humidity Sensor (3 pins)

Operational Amplifier, Op Amp + Comparator + Reference

Resistor 10k ohm

LED (generic)

Jumper wires (generic)

Micro-USB to USB Cable (Generic)

Software apps and online services

Particle Build Web IDE

ThingSpeak API

Story

Background

Being that it is spring, and in the state of North Carolina, you never know what the weather is going to be like at the start of each day. We created this IOT project with the goal of being able to know the temperature and humidity inside your home/office without the need of looking at the thermostat. To accomplish this, two Particle Photons were used. The first was connected to a temperature/humidity sensor (DHT11), which would record the present temperature and humidity which is then published to the internet. The second Photon was connected to the humidifier itself which was subscribed to the data published by the first Photon.

How it Works- Temperature/Humidity Sensor

The first Photon, referenced as DHT11 Sensor in the wiring diagram and code attachment, was responsible for recording the temperature/humidity and then publish this data to the internet. The photon was set to record the temperature every 15 seconds. To test the sensor, we placed the photon inside and allowed it to record and publish data. ThingSpeak was paired with the Photon over this period so that it could be used to plot the temperature versus the time and the humidity versus time recorded. Below is the ThingSpeak graph displaying the temperature/humidity data over this time period. Note that the Temperature/Humidity Sensor code includes library codes "PietteTech_DHT.h" and "ThingSpeak.h".

How it Works- Humidifier Controller

The first Photon, referenced as Humidifier Sensor in the wiring diagram and code attachment, was responsible for taking the published data from the internet and using that against a set point. The photon had a set point which when this set point was exceeded the photon turned the humidifier off. On the other hand, if the data is reading under the set point then the humidifier continues to run. The photons together each have an LED that is lit to notify the user that the humidifier is active and if it is not lit the humidifier is currently turned off. Note that the Humidifier Sensor code includes library codes "math.h".

Live Graph Link

https://thingspeak.com/channels/758578

Temperature/Humidity Sensor Breadboard

DHT11 Hookup

The Controlling Humidifier Breadboard

Humidifier

Youtube Video of the Entire IOT project working

Code

// This #include statement was automatically added by the Particle IDE.
#include <PietteTech_DHT.h>

#include "ThingSpeak.h"

#define DHTTYPE  DHT11      // Sensor type DHT11/21/22/AM2301/AM2302
#define DHTPIN   3          // Digital pin for communications


PietteTech_DHT DHT(DHTPIN, DHTTYPE);

int n=0;      // counter
int LEDpin=D6;
float h_set=90;

bool humid = false;

TCPClient client;


unsigned long myChannelNumber = 758578;
const char * myWriteAPIKey = "J9R2AAQEJK14M5W9";

void setup() {
  ThingSpeak.begin(client);
  
  Serial.begin(9600);
  pinMode (D3, INPUT);
  pinMode (LEDpin,OUTPUT);
  
  bool humid = false;
    
     Particle.publish("humiditysensorthreshold", "off");
     Particle.subscribe("heaterblockon", myHandler);
  
}

void loop() {
  int result = DHT.acquireAndWait(1000); // wait up to 1 sec (default indefinitely)

  switch (result) {
  case DHTLIB_OK:
    Serial.println("OK");
    break;
  case DHTLIB_ERROR_CHECKSUM:
    Serial.println("Error\n\r\tChecksum error");
    break;
  case DHTLIB_ERROR_ISR_TIMEOUT:
    Serial.println("Error\n\r\tISR time out error");
    break;
  case DHTLIB_ERROR_RESPONSE_TIMEOUT:
    Serial.println("Error\n\r\tResponse time out error");
    break;
  case DHTLIB_ERROR_DATA_TIMEOUT:
    Serial.println("Error\n\r\tData time out error");
    break;
  case DHTLIB_ERROR_ACQUIRING:
    Serial.println("Error\n\r\tAcquiring");
    break;
  case DHTLIB_ERROR_DELTA:
    Serial.println("Error\n\r\tDelta time to small");
    break;
  case DHTLIB_ERROR_NOTSTARTED:
    Serial.println("Error\n\r\tNot started");
    break;
  default:
    Serial.println("Unknown error");
    break;
  }

  n++;
  
int humidity = DHT.getHumidity();
int temperature = DHT.getFahrenheit();
  
if(DHT.getHumidity()<h_set){
        Particle.publish("humiditysensorthreshold", "on");
    }
    else {
        Particle.publish("humiditysensorthreshold", "off");
    }


  ThingSpeak.setField(1,humidity);
  ThingSpeak.setField(2,temperature);
  
  Serial.print(DHT.getHumidity());
Serial.println("h");
Serial.print(DHT.getFahrenheit());
Serial.println("t");

  
  ThingSpeak.writeFields(myChannelNumber, myWriteAPIKey);  

  delay(15000); // ThingSpeak will only accept updates every 15 seconds. 
}

void myHandler(String event, String data)
{
    if(data == "on"){
        digitalWrite(LEDpin,HIGH);}
     if(data == "off"){
        digitalWrite(LEDpin,LOW);}
}

#include <math.h>
int ThermistorPin = A0;
int PWM_Pin = D3;
int LEDpin= D5;

int EState;
int ELastState;
int counter=0;

int Resistor1 = 10000;
int B=3950;// thermistor beta coefficient
int samples[8];
int i;
float Therm_resistance;
double T;
float Vout;

float kp = 6;   
float ki = 0.5;   
float PID_p=0;    float PID_i=0;
float PID_error=0;
float PID_value=0;

int set_temperature = 220;

float previous_error;
float elapsedTime, timePrev;

void setup() {
    Particle.publish("heaterblockon", "off");
    Particle.subscribe("humiditysensorthreshold", myHandler);
Serial.begin(9600);

pinMode (PWM_Pin, OUTPUT);
pinMode (ThermistorPin,INPUT);
pinMode (LEDpin, OUTPUT);
digitalWrite(LEDpin,LOW);

  
}

void loop() {

  Vout = analogRead(ThermistorPin);
 for (i=0; i< 8; i++) {
   samples[i] = analogRead(ThermistorPin);
   delay(10);
  }
 
  // average all the samples out
  Vout = 0;
  for (i=0; i< 8; i++) {
     Vout += samples[i];
  }
  Vout /= 8;

  //To find thermistor resistance
  Therm_resistance = Resistor1 / (4095/Vout-1);
  //Steinhart_Hart equation, ouputs in kelvin
  T = (1/(((log(Therm_resistance / 10000))/B)+(1.0 / (25 + 273.15))));
  //convert to celcius
  T = T - 273.15;
  //convert to farenheit
  T = (T * 9.0)/ 5.0 + 32.0; 
 
  //calculate the error
  PID_error = set_temperature - T;

//calculations needed for PID_p
   PID_p=PID_error;
  
  //Calculate the I value 
    PID_i += (PID_error);
    if (PID_i>50){
      PID_i=50;
    }
    if (PID_i<-50){
      PID_i=-50;
    }
    else{
     PID_i=PID_i;
    }
     
  //Final total PID value 
  PID_value = (PID_p*kp) + (PID_i*ki);
  
  //PWM range between 0 and 255 (0-100 duty cycle)
  if(PID_value < 0)
  {    PID_value = 0;    }
  if(PID_value > 255)  
  {    PID_value = 255;  }
  else PID_value=PID_value;
 
  {analogWrite(PWM_Pin,PID_value);  
  //digitalWrite(LEDpin, HIGH);}
  }
    previous_error = PID_error;
    
    Serial.print(PID_value);
Serial.println("pid");
Serial.print(set_temperature);
Serial.println("tset");
Serial.print(PID_i);
Serial.println("i");
Serial.print(set_temperature);
Serial.println("t");

  
  delay(1000);
}

void myHandler(String event, String data)
{
    if(data == "on"){
    Particle.publish("heaterblockon", "on");
        set_temperature=220;
        digitalWrite(LEDpin,HIGH);}
     if(data == "off"){
        Particle.publish("heaterblockon", "off");
        set_temperature=0;
        digitalWrite(LEDpin,LOW);}
}

Credits

John Ranshaw

1 project • 0 followers

Christopher Ames

1 project • 0 followers

Temperature and Humidity Sensor Controlling Humidifier