# Code for reading Photoresistor and DHT11, print on a LCD and buzzer for alarm

**URL:** <https://forum.arduino.cc/t/code-for-reading-photoresistor-and-dht11-print-on-a-lcd-and-buzzer-for-alarm/365102>\
**Category:** Sensors\
**Created:** [February 13, 2016, 2:58am UTC](https://forum.arduino.cc/t/code-for-reading-photoresistor-and-dht11-print-on-a-lcd-and-buzzer-for-alarm/365102 "2016-02-13T02:58:13Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![jpiccino](https://avatars.discourse-cdn.com/v4/letter/j/71e660/32.png) [@jpiccino](https://forum.arduino.cc/u/jpiccino)\
**Post date:** [February 13, 2016, 2:58am UTC](https://forum.arduino.cc/t/code-for-reading-photoresistor-and-dht11-print-on-a-lcd-and-buzzer-for-alarm/365102/1 "2016-02-13T02:58:13Z")

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I am just starting with Arduino and I made an sketch from several others and included some code of my own and I want to know what the mistakes I made on the code / electronics.

The code starts with the connections and is all commented, as I intend to publish it to other begginers.

```cpp
/* Connections
******
BUZZER:
NEGATIVE PIN: GND
POSITIVE PIN: PWM6

******
DHT 11
WITH THE HOLES FACING YOU
PIN 1 5V
PIN 2 A0
PIN 3 EMPTY
PIN 4 GND

***********
Potentiometer facing you
left: GND
MIDDLE: LCD PIN 3
RIGHT: 5V

***********
Photoresistor
One leg to 5V
The other leg to A2 and 10k resistor (brown, black, orange) to GND

***********
LCD pin - Arduino Pin
Pin 1 (VSS) - GND
Pin 2 (VDD) - 5V
Pin 3 V0 - POTENTIOMETER 10K OHMS CENTRAL PIN
Pin 4 RS - PWM12
Pin 5 R/W - GND
Pin 6 E - PWM11
Pin 11 D-4 - PWM5
Pin 12 D-5 - PWM4
Pin 13 D-6 - PWM3
Pin 14 D-7 - PWM2
Pin 15 A (BACKLIGHT) - 220 OHM (RED RED BROWN) - A1 // The lcd backlight I connected to pin A1, so it can be turned off
Pin 16 K (BACKLIGHT) - GND
THE RESISTOR ON PIN 15 MAKES THE LCD DRAW LESS POWER FROM ARDUINO
*/

// INCLUDING LIBRARIES FOR 16X2 LCD, DHT and time
#include <TimeLib.h>
#include <LiquidCrystal.h>
#include <dht.h>

#define dht_dpin A0 // THIS NEXT PINS CAN BE CHANGED IF NEEDED.
#define bklt A1     

LiquidCrystal lcd(12, 11, 5, 4, 3, 2); // Calls the LCD library and set the pins

dht DHT;                               // Names the dht library DHT
int freq;                              // Creates a variable named freq.
int ledPin = 13;
int cic = 0;                           // Set the counter to zero
// Photosensor
int PhotoPin = A2;    // select the input pin for the sensor
int PhotoValue = 0;  // variable to store the value coming from the sensor
int minLight;          //Used to calibrate the readings
int maxLight;          //Used to calibrate the readings
int lightLevel;
int adjustedLightLevel;
int off = 0;

void setup() {
  pinMode(ledPin, OUTPUT);        // Makes the pin 13 output
  digitalWrite(ledPin, LOW);       // Turn off the board led attached to pin 13 off.
  pinMode(bklt, OUTPUT);          // Makes the Backlight switchable
  digitalWrite(bklt, HIGH);        // Turns the Backlight On
  lcd.begin(16, 2);               // Starts the LCD
  lcd.clear();                    // Clears the LCD
  lcd.display();                  // Turns the LCD on
  lcd.setCursor(0, 0);            // Puts the cursor on the first digit of the first line
  lcd.print("Temperature & Hu");  // Writes the first line
  lcd.setCursor(0, 1);            // Puts the cursor on the first digit of the second line
  lcd.print("midity Sensors");    // Writes the second line
  delay(2000);                    // Wait rest of 1000ms recommended delay before accessing sensor
  second(0);
}                                 //end "setup()"

void loop() {
  if (lightLevel <= 15) {       /* Turns off the backlight if the light read in the previous loop is 
                                   too low, so the backlight does not interfere in the next reading. */
    digitalWrite(bklt, LOW);
    delay(100);
    off = 1;                      // Sets the variable to determine a 100ms shorter final delay
  }
  if (lightLevel > 15) {
    off = 2;                      // Sets the variable to determine a 2 minutes final delay
  }
  // auto-adjust the minimum and maximum limits in real time
  lightLevel = analogRead(PhotoPin);
  if (minLight > lightLevel) {
    minLight = lightLevel;
  }
  if (maxLight < lightLevel) {
    maxLight = lightLevel;
  }
  digitalWrite(bklt, HIGH);
  cic = (cic + 1); // Add 1 to the number of cycles
  DHT.read11(dht_dpin); // THIS READING MUST HAVE AT LEAST A 2 SECONDS INTERVAL.
  lcd.display(); // Turns the display back on (it is turned off at the end of the loop)
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print(lightLevel);lcd.print(" ");	/* Prints the light measured by the photoresistor.
   The A/D converter sets a scale from 1 to 1023. */
  lcd.print(DHT.temperature, 0);	// Prints the temperature from DHT. The <, 0> instructs to print no decimals
  lcd.print((char)223); // Prints the degree sign
  lcd.print("C ");
  lcd.print(DHT.humidity, 0); // Prints the humidity from DHT. The <, 0> instructs to print no decimals
  lcd.print("% ");
  //lcd.print("L:");
  lcd.setCursor(0, 1);
  /*lcd.print("C");*/ lcd.print(cic); //Prints the number of cycles runned since turned on.
  lcd.print(" "); lcd.print(day()); lcd.print("d"); lcd.print(hour()); printDigits(minute()); //Prints time since turned on.
  if (DHT.temperature >= 32 ) { // Sets a buzzer alarm if the measured temperature is at least 32C
    freq = 2000 + DHT.temperature;	// Sets the variable frequency
    tone(6, freq, 500); // Buzz for half a second
  }
  if (DHT.humidity < 35 ) { // Sets a buzzer alarm if the measured humidity is bellow 35%
    freq = 300; tone(6, freq, 500);	// Sets the frequency and plays it for half a second
  }
  if (off == 1) {
    delay(119900);                      // waits 1.9 minutes to start the loop again. With the 100ms delay on line 89, the total loop interval will be 2 minutes.
  }
  if (off == 2) {delay(120000);}         // Waits 2 minutes to start the loop again.
}// end loop()

void printDigits(int Digits) {
  // utility function for digital clock display: prints preceding colon and leading 0
  lcd.print("h");
  if (Digits < 10)
    lcd.print('0');
  lcd.print(Digits);
}

```

[DHT11\_photo\_buzzer\_LCD\_AlwaysOn.ino](https://forum.arduino.cc/uploads/short-url/pfyQaUqnuYGZI7NJGrRSUINhniW.ino) (5.03 KB)

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**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\
**Post date:** [May 6, 2021, 10:12am UTC](https://forum.arduino.cc/t/code-for-reading-photoresistor-and-dht11-print-on-a-lcd-and-buzzer-for-alarm/365102/2 "2021-05-06T10:12:17Z")

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