Second project - Temperature + humidity + LCD!

Hello coders, hackers, makers and curious visitors!

   The second project I worked on is a "temperature and humidity sensor with a LCD display" based on Arduino, the DHT11 serial temperature/humidity sensor, the LM35 linear temperature sensor and a 16x2 LCD screen. The project is similar to this one and features readings of temperature and humidity that are shown in a LCD display and sent via Arduino (USB- serial) to any PC terminal. Below I show a picture of the project working:

The prototype, when compared to Google Weather (upper right corner)

   The serial console (on arduino IDE) can be seen below, capturing successive readings from Arduino serial:

Screenshot of data captured through serial

   The complete schematic of this prototype is in the picture below; it was developed using Fritzing; You can download the schematic here. 

   The project was coded inside the Arduino IDE using some third-part codes, which I put together and made it work. The original codes are: DHT11 Library and LiquidCrystal . My code is available in the box below, as well as in this Github link.

/*
 Modified by Clovis Fritzen in June 11th, 2014:
 - The original program read the serial temperature/humidity sensor DHT11 (which is still part of this program); 
 - "Delay" function substituted by a counter (when the counter overflows the program enters the serial routine)
 - Added the LM35 (10mV/C temperature sensor) reading via serial, to compare both sensors
 */
/*
  Board           int.0   int.1   int.2   int.3   int.4   int.5
 Uno, Ethernet   2   3
 Mega2560   2   3   21   20   19   18
 Leonardo   3   2   0   1
 Due           (any pin, more info http://arduino.cc/en/Reference/AttachInterrupt)
 
 This example, as difference to the other, make use of the new method acquireAndWait()
 */
 
#include 
#include 

int idDHT11pin = 2; //Digital pin for comunications
int idDHT11intNumber = 0; //interrupt number (must be the one that use the previus defined pin (see table above)
long count= 0; // counter for spacing the serial writings
long AcqPeriod= 0;
int sensorPin = A5; // input pin for LM35 (10mV/C)
int sensorValue = 0; // variable to store the LM35 temperature
int led= 13;


//declaration
void dht11_wrapper(); // must be declared before the lib initialization

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(9, 8, 5, 4, 3, 6);

// Lib instantiate
idDHT11 DHT11(idDHT11pin,idDHT11intNumber,dht11_wrapper);

void setup()
{
  pinMode(led, OUTPUT);   
  Serial.begin(9600);
  Serial.println("DHT11 temp/humidity sensor - Example program");
  Serial.print("Lib version: ");
  Serial.println(IDDHT11LIB_VERSION);
  Serial.println("modified by Clovis Fritzen");
  Serial.println("---------------");
  
   // set up the LCD's number of columns and rows: 
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.print(" DHT:|LM35:|HUM:");
}
// This wrapper is in charge of calling 
// mus be defined like this for the lib work
void dht11_wrapper() {
  DHT11.isrCallback();
}
void loop()
{
  
  AcqPeriod= 400000; // set here the interval in which data is sent into serial 
  
  if (count < AcqPeriod) // Still need to make sure what this number represents in terms of
                      // seconds or cycles of clock
  {
  count= count++;
  
  if (count < (AcqPeriod/2)) // just a routine to blink a led :)
  {
    digitalWrite(led, HIGH);
  } else{
    digitalWrite(led, LOW);
  }
 }
else
{
  
  //Serial.print("\nRetrieving information from sensor: ");
  Serial.print("\nRead sensor: ");
  //delay(100);
 count= '0';
 
 sensorValue = analogRead(sensorPin);
 sensorValue= sensorValue/2;
  
  int result = DHT11.acquireAndWait();
  switch (result)
  {
  case IDDHTLIB_OK: 
    Serial.println("done"); 
    break;
  case IDDHTLIB_ERROR_CHECKSUM: 
    Serial.println("Error\n\r\tChecksum error"); 
    break;
  case IDDHTLIB_ERROR_ISR_TIMEOUT: 
    Serial.println("Error\n\r\tISR time out error"); 
    break;
  case IDDHTLIB_ERROR_RESPONSE_TIMEOUT: 
    Serial.println("Error\n\r\tResponse time out error"); 
    break;
  case IDDHTLIB_ERROR_DATA_TIMEOUT: 
    Serial.println("Error\n\r\tData time out error"); 
    break;
  case IDDHTLIB_ERROR_ACQUIRING: 
    Serial.println("Error\n\r\tAcquiring"); 
    break;
  case IDDHTLIB_ERROR_DELTA: 
    Serial.println("Error\n\r\tDelta time to small"); 
    break;
  case IDDHTLIB_ERROR_NOTSTARTED: 
    Serial.println("Error\n\r\tNot started"); 
    break;
  default: 
    Serial.println("Unknown error"); 
    break;
  }
  
  lcd.setCursor(7, 1);
  // print the number of seconds since reset:
  lcd.print(sensorValue);
  
  Serial.print("Humidity (%): ");
  Serial.println(DHT11.getHumidity(), 0); // ", 0" represents the number of decimal positions after the comma

  Serial.print("DHT11 Temp (oC): ");
  Serial.println(DHT11.getCelsius(), 0); // ", 0" represents the number of decimal positions after the comma
  
  lcd.setCursor(13, 1);
  // print the number of seconds since reset:
  lcd.print(DHT11.getHumidity(), 0);
  
  Serial.print("LM35 Temp (oC): ");
  Serial.println(sensorValue);
  

  //Serial.print("Temperature (oF): ");
  //Serial.println(DHT11.getFahrenheit(), 2);

  //Serial.print("Temperature (K): ");
  //Serial.println(DHT11.getKelvin(), 2);

  //Serial.print("Dew Point (oC): ");
  //Serial.println(DHT11.getDewPoint());

  //Serial.print("Dew Point Slow (oC): ");
  //Serial.println(DHT11.getDewPointSlow());
  
   // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(1, 1);
  // print the number of seconds since reset:
  lcd.print(DHT11.getCelsius(),0);
  
   }
  
  }

   I just want to share some notes with you:
- Both the DHT11 and LM35 have a "step" (or resolution) of one degree Celsius, meaning they cannot read something like "26.3"; They a only capable of reading numbers with no decimal (e.g: "26").
- The contrast of the LCD screen can be adjusted by means of the potentiometer; Its backlight is always on (last two pins of the LCD on the schematic above).
- The circuit works independently on the presence of the USB cable on Arduino; it means that it will work on batteries for example!. in this case only the serial readings will be missing.
- The is a blinking led on pin 13 of Arduino (which is assemble on the board); That one is there just for fun.

   I hope you guys are enjoying my posts so far, and trying to validate my projects by doing it yourselves. If you have any suggestions/ recommendations or critics, please feel free to talk to me on Twitter, Google Plus and Facebook, as well as in the comments below. See you all next time!.

First project - Arduino Binary Thermometer with LM35

Hello folks! 

   As a first project post I will show you the steps I take to develop a binary thermometer with a LM35 temperature sensor. It is a bit similar to this one from instructables, but mine is arduino-powered. My intention on this project was simply to test the power of arduino (UNO R3) on handling one of its ports (6 bits) at a time, and also the efficacy of the LM35 digital temperature sensor.

The prototype schematic

   The schematic I created was drawn in Fritzing. My code (also available below) can be found in GitHub ( here). It is important to notice that the limits of temperatures that can be read are NOT the ones of the LM35, instead they are limited by the Arduino power supply voltage (0 +5V): so you are able to read  temperatures between +2 and +150 degrees Celsius.

// Arduino timer CTC interrupt example (timer), from www.engblaze.com
// This example is a binary meter - shows a analog value in a binary (6-bit) output
// Modified by Clovis Fritzen, to fit as a binary thermomter (in may/2014)
 
// avr-libc library includes
#include < avr/io.h >
#include < avr/interrupt.h >
 
int sensorPin = A0;    // select the input pin for the potentiometer
int sensorValue = 0;  // variable to store the value coming from the sensor (LM35)
byte binaryValue= B00000000; // initialize port value as zeros

void setup()
{
    DDRB = DDRB | B00111111; // set 6 pins in port B as outputs
    
    // initialize Timer1
    cli();          // disable global interrupts
    TCCR1A = 0;     // set entire TCCR1A register to 0
    TCCR1B = 0;     // same for TCCR1B
 
    // set compare match register to desired timer count:
    OCR1A = 15624; // for temperature
    // turn on CTC mode:
    TCCR1B |= (1 << WGM12);
    // Set CS10 and CS12 bits for 1024 prescaler:
    TCCR1B |= (1 << CS10);
    TCCR1B |= (1 << CS12);
    // enable timer compare interrupt:
    TIMSK1 |= (1 << OCIE1A);
    // enable global interrupts:
    sei();
}
 
void loop()
{
    // You would put another stuff program here
}
 
ISR(TIMER1_COMPA_vect)
{
  // read the value from the sensor  :
  sensorValue = analogRead(sensorPin);
  //digitalValue= sensorValue;
  binaryValue= byte(sensorValue/2);
  PORTB = binaryValue; 
}

   Some notes:

- The LM35 sensor is connected to the analog input A0;

- I put three colors of leds only to give an impression of "the warmer the color, the warmer the ambient (since the MSB is a red led, connected to pin 13 of arduino);

- I have only tested it indoors so far, and it showed to be accurate enough for a sensor like that, when compared to a DTH11 temperature sensor. 

I hope you have liked it, and I promised I will try to put some videos of the actual circuits working, for the next experiments.