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The LM35 is an inexpensive, precision Centigrade temperature sensor made by Texas Instruments. It provides an output voltage that is linearly proportional to the Centigrade temperature and is, therefore, very easy to use with the Arduino.

The sensor does not require any external calibration or trimming to provide accuracies of ±0.5°C at room temperature and ±1°C over the −50°C to +155°C temperature range.

One of the downsides of the sensor is that it requires a negative bias voltage to read negative temperatures. So if that is needed for your project, I recommend using the DS18B20 or TMP36 instead. The TMP36 by Analog Devices is very similar to the LM35 and can read temperatures from -40°C to 125°C without any external components.

The pinout of the sensor:

Note that pin 1 (+V_S) is the leftmost pin when the flat side of the sensor (with the text printed on it) is facing towards you.

Pin1: +VS  - Positive power supply pin (4 – 30 V)
Pin2: Vout - Temperature sensor analog output
Pin3: GND  - Device ground pin

Source code of Arduino sketch:

#define sensorPin A0

void setup() {
  // Begin serial communication at a baud rate of 9600:
  Serial.begin(9600);

  // Set the reference voltage to the built-in 1.1V reference:
  analogReference(INTERNAL);
}
void loop() {
  // Get a reading from the temperature sensor:
  int reading = analogRead(sensorPin);

  // Convert the reading into voltage:
  float voltage = reading * (1100 / 1024.0);

  // Convert the voltage into the temperature in degree Celsius:
  float temperature = voltage / 10;

  // Print the temperature in the Serial Monitor:
  Serial.print(temperature);
  Serial.print(" \xC2\xB0"); // shows degree symbol
  Serial.println("C");
  delay(1000); // wait a second between readings
}

DS1302, DS1307, DS3231 is a real-time modules for Arduino and Raspberry PI. Let’s connect DS3231 to our Arduino NANO.

To work with this module we will use universal library: iarduino_RTC (https://github.com/tremaru/iarduino_RTC).

Download latest version of this library you can here: https://github.com/tremaru/iarduino_RTC/archive/refs/tags/1.3.4.zip

First of all connect DS3231 module to Arduino:

GND (-) --> GND
VCC (+) --> +5V
SDA (D) --> A4
SCL (C) --> A5

Include library and initialize module:

#include <iarduino_RTC.h>
iarduino_RTC time(RTC_DS1307);

To set current time in DS3231 module tuesday write next functions in function setup():

void setup() {
    Serial.begin(9600);
    time.begin();
    time.settime(0,20,17,30,3,21,2);  
    // 0  sec, 20 min, 17 hour, 30 day, 3 mon, 2021 year, tuesday
}

In function loop() let’s write to serial port current time:

void loop(){
    if(millis() % 1000 == 0) {
        Serial.println(time.gettime("d-m-Y, H:i:s, D"));
        delay(1);
    }
}

This sketch you need to run once time, when configure DS3231 module.

If you want just to show current time – use this source code:

#include 
iarduino_RTC time(RTC_DS1307);

void setup() {
    Serial.begin(9600);
}
void loop() {
    if(millis() % 1000 == 0) {
        Serial.println(time.gettime("d-m-Y, H:i:s, D"));
        delay(1);
    }
}

In this Instructable you are going to see how to connect i2c lcd display to arduino and how to print on lcd display.

Each I2C bus consists of two signals: SCL and SDA. SCL is the clock signal, and SDA is the data signal. The clock signal is always generated by the current bus master; some slave devices may force the clock low at times to delay the master sending more data (or to require more time to prepare data before the master attempts to clock it out). This is called “clock stretching” and is described on the protocol page.

To connect 16×2 LCD display to Arduino we use i2c PCF 8574T module. This module expands Arduino pins and allow connection of display using only two Arduino pins.

I2C module has four pins: GND – ground, VCC – 5V power, SDA – data signal, SCL – clock signal. Connect SDA to A4 pin on Arduino, and SCL to A5 pin:

GND <---> GND
VCC <---> 5V
SDA <---> A4
SCL <---> A5

For working with display on Arduino we need two libraries: Wire.h, LiquidCrystal_I2C.h.

Wire.h is standard Arduino IDE library, and LiquidCrystal_I2C.h is the library for work with LCD displays. You can download it from official Arduino project website: https://www.arduino.cc/reference/en/libraries/liquidcrystal-i2c/

And here is the source code of simple sketch, which write text on 16×2 LCD display:

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,16,2);

void setup() 
{
  lcd.init();
  lcd.backlight();

  lcd.setCursor(0,0); // set cursor to 1 symbol of 1 line
  lcd.print("Arduino Lessons:");

  lcd.setCursor(0,1); // set cursor to 1 symbol of 2 line
  lcd.print("www.andjey.info"); 
}

void loop() 
{  

}

Let’s write simple program, that will turn on and off LED on our Arduino. For our lesson we need: Arduino, one LED diode, USB cable for programming our Arduino, PC with Arduino IDE, download it you can here: https://www.arduino.cc/en/software

Connect USB cable to Arduino, for connecting LED we will use D13 pin and GND PIN (see Arduino Nano pins here). Positive wire of diode connect to D13, negative wire – to Ground pin as you can see on photo:

In Arduino IDE create new blank project:

Here You can see two functions: setup() – which run when Arduion power on, and function loop() – which run in cycle all type when arduino is working. Now let’s create our program.

Bewore function start() let’s create two constants – it will be basic configuration of our program. BLINK_PIN defines which pin is used for connecting LED. BLINK_TIME – define time in milliseconds how long our LED will be on and off.

#define BLINK_PIN 13
#define BLINK_TIME 1000

In function setup() configure pin 13 as output pin:

void setup() {
  pinMode(BLINK_PIN,1);
}

Now create function blink_led() – that will turn on and off our LED:

void blink_led()
{
  digitalWrite(BLINK_PIN, 1);
  delay(BLINK_TIME);
  
  digitalWrite(BLINK_PIN, 0);
  delay(BLINK_TIME);
}

Now write function blink_led() in loop() to run our program in cycle all time when Arduino works:

void loop() {
  blink_led();
}

Full code of program:

#define BLINK_PIN 13
#define BLINK_TIME 300

void blink_led()
{
  digitalWrite(BLINK_PIN, 1);
  delay(BLINK_TIME);
  
  digitalWrite(BLINK_PIN, 0);
  delay(BLINK_TIME);
}

void setup() {
  pinMode(BLINK_PIN,1);
}

void loop() {
  blink_led();
}

Now save program and compile it to your Arduino: