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!.
