user21038: so I will explain what I want to get.
I am reading temperature from DS18B20 and showing it on the LCD. 
I have one LED o pin 3 which is blinking when there is a temp reading and screen update. I have another LED on pin 4 which should lit when temp is more than 25 and less than 30, and I want it to blink when temp is more than 30. What I am getting is a blinking but not like one blink every 10ms but it waits for whole loop to start again to blink.
Can I do it separately that this LED will blink indepentantly when condition is true? With set interval for example 10ms which wont be waiting for whole loop.
here is my example code:
    #include <OneWire.h>

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



LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  // Set the LCD I2C address

//LiquidCrystal_I2C lcd(0x27, POSITIVE);  // Set the LCD I2C address
OneWire  ds(2);

unsigned long previousMillis = 0;
const long interval = 1000;
int ledState = LOW;
void setup()
{
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);

  lcd.begin(16,2);               // initialize the lcd 

}

void loop()

{
  unsigned long currentMillis = millis();

  byte i;
  byte present = 0;
  byte type_s;
  byte data[12];
  byte addr[8];
  float celsius;

  if ( !ds.search(addr)) {
    ds.reset_search();
    delay(250);
    return;
  }

  Serial.println();

  // the first ROM byte indicates which chip
  switch (addr[0]) {
    case 0x10:
      Serial.println("  Chip = DS18S20");  // or old DS1820
      type_s = 1;
      break;
    case 0x28:
      Serial.println("  Chip = DS18B20");
      type_s = 0;
      break;
    case 0x22:
      Serial.println("  Chip = DS1822");
      type_s = 0;
      break;
    default:
      Serial.println("Device is not a DS18x20 family device.");
      return;
  } 

  ds.reset();
  ds.select(addr);
  ds.write(0x44, 1);        // start conversion, with parasite power on at the end

  delay(850);     // maybe 750ms is enough, maybe not
  // we might do a ds.depower() here, but the reset will take care of it.

  present = ds.reset();
  ds.select(addr);    
  ds.write(0xBE);         // Read Scratchpad

  Serial.print("  Data = ");
  Serial.print(present, HEX);
  Serial.print(" ");
  for ( i = 0; i < 9; i++) {           // we need 9 bytes
    data[i] = ds.read();
    Serial.print(data[i], HEX);
    Serial.print(" ");
  }
  Serial.print(" CRC=");
  Serial.print(OneWire::crc8(data, 8), HEX);
  Serial.println();

  // Convert the data to actual temperature
  // because the result is a 16 bit signed integer, it should
  // be stored to an "int16_t" type, which is always 16 bits
  // even when compiled on a 32 bit processor.
  int16_t raw = (data[1] << 8) | data[0];
  if (type_s) {
    raw = raw << 3; // 9 bit resolution default
    if (data[7] == 0x10) {
      // "count remain" gives full 12 bit resolution
      raw = (raw & 0xFFF0) + 12 - data[6];
    }
  } else {
    byte cfg = (data[4] & 0x60);
    // at lower res, the low bits are undefined, so let's zero them
    if (cfg == 0x00) raw = raw & ~7;  // 9 bit resolution, 93.75 ms
    else if (cfg == 0x20) raw = raw & ~3; // 10 bit res, 187.5 ms
    else if (cfg == 0x40) raw = raw & ~1; // 11 bit res, 375 ms
    //// default is 12 bit resolution, 750 ms conversion time
  }
  celsius = (float)raw / 16.0;


  digitalWrite(3, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(10);              // wait for a second
  digitalWrite(3, LOW);    // turn the LED off by making the voltage LOW


   lcd.home ();
   lcd.print("Reading 1");
   lcd.setCursor( 0, 1);
   lcd.print("temp:");
   lcd.print(celsius);
   lcd.print("*C");

   if (celsius >= 25 && celsius < 30) {
    digitalWrite(4,HIGH);
   } else if (celsius >= 30) {
blink1();
   } else {
    digitalWrite(4,LOW);
   }

}

void blink1() {
digitalWrite(4,HIGH);
delay(50);
digitalWrite(4,LOW);
}


user20208: Here try this:
#include <OneWire.h>

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



LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  // Set the LCD I2C address

//LiquidCrystal_I2C lcd(0x27, POSITIVE);  // Set the LCD I2C address
OneWire  ds(2);

const long interval = 1000; //İnterval at which to blink(milliseconds)
unsigned long previousMillis = 0;
int ledState = LOW;
void setup()
{
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);

  lcd.begin(16,2);               // initialize the lcd 

}

void loop()
{

  byte i;
  byte present = 0;
  byte type_s;
  byte data[12];
  byte addr[8];
  float celsius;

  if ( !ds.search(addr)) {
    ds.reset_search();
    delay(250);
    return;
  }

  Serial.println();

  // the first ROM byte indicates which chip
  switch (addr[0]) {
    case 0x10:
      Serial.println("  Chip = DS18S20");  // or old DS1820
      type_s = 1;
      break;
    case 0x28:
      Serial.println("  Chip = DS18B20");
      type_s = 0;
      break;
    case 0x22:
      Serial.println("  Chip = DS1822");
      type_s = 0;
      break;
    default:
      Serial.println("Device is not a DS18x20 family device.");
      return;
  } 

  ds.reset();
  ds.select(addr);
  ds.write(0x44, 1);        // start conversion, with parasite power on at the end

  delay(850);     // maybe 750ms is enough, maybe not
  // we might do a ds.depower() here, but the reset will take care of it.

  present = ds.reset();
  ds.select(addr);    
  ds.write(0xBE);         // Read Scratchpad

  Serial.print("  Data = ");
  Serial.print(present, HEX);
  Serial.print(" ");
  for ( i = 0; i < 9; i++) {           // we need 9 bytes
    data[i] = ds.read();
    Serial.print(data[i], HEX);
    Serial.print(" ");
  }
  Serial.print(" CRC=");
  Serial.print(OneWire::crc8(data, 8), HEX);
  Serial.println();

  // Convert the data to actual temperature
  // because the result is a 16 bit signed integer, it should
  // be stored to an "int16_t" type, which is always 16 bits
  // even when compiled on a 32 bit processor.
  int16_t raw = (data[1] << 8) | data[0];
  if (type_s) {
    raw = raw << 3; // 9 bit resolution default
    if (data[7] == 0x10) {
      // "count remain" gives full 12 bit resolution
      raw = (raw & 0xFFF0) + 12 - data[6];
    }
  } else {
    byte cfg = (data[4] & 0x60);
    // at lower res, the low bits are undefined, so let's zero them
    if (cfg == 0x00) raw = raw & ~7;  // 9 bit resolution, 93.75 ms
    else if (cfg == 0x20) raw = raw & ~3; // 10 bit res, 187.5 ms
    else if (cfg == 0x40) raw = raw & ~1; // 11 bit res, 375 ms
    //// default is 12 bit resolution, 750 ms conversion time
  }
  celsius = (float)raw / 16.0;

   lcd.home ();
   lcd.print("Reading 1");
   lcd.setCursor( 0, 1);
   lcd.print("temp:");
   lcd.print(celsius);
   lcd.print("*C");

   if (celsius >= 25 && celsius < 30) {
    digitalWrite(4,HIGH);
   } else if (celsius >= 30) {
blink1();
   } else {
    digitalWrite(4,LOW);
   }

   unsigned long currentMillis = millis();

   if (currentMillis - previousMillis >= interval) {

     previousMillis = currentMillis;

     if (ledState == LOW) {
       ledState = HIGH;
     } else {
       ledState = LOW;
     }

     digitalWrite(3, ledState);
   }
}

void blink1() {
digitalWrite(4,HIGH);
delay(50);
digitalWrite(4,LOW);
}

and also note that i choosed 1000 milliseconds for interval (equal to 1 second) so if you want 10ms as in your first post then change const long interval to 10

21038: <p>so I will explain what I want to get.
I am reading temperature from DS18B20 and showing it on the LCD. 
I have one LED o pin 3 which is blinking when there is a temp reading and screen update. I have another LED on pin 4 which should lit when temp is more than 25 and less than 30, and I want it to blink when temp is more than 30. What I am getting is a blinking but not like one blink every 10ms but it waits for whole loop to start again to blink.
Can I do it separately that this LED will blink indepentantly when condition is true? With set interval for example 10ms which wont be waiting for whole loop.</p>

<p>here is my example code:</p>

<pre><code>    #include &lt;OneWire.h&gt;

#include &lt;Wire.h&gt; 
#include &lt;LiquidCrystal_I2C.h&gt;



LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  // Set the LCD I2C address

//LiquidCrystal_I2C lcd(0x27, POSITIVE);  // Set the LCD I2C address
OneWire  ds(2);

unsigned long previousMillis = 0;
const long interval = 1000;
int ledState = LOW;
void setup()
{
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);

  lcd.begin(16,2);               // initialize the lcd 

}

void loop()

{
  unsigned long currentMillis = millis();

  byte i;
  byte present = 0;
  byte type_s;
  byte data[12];
  byte addr[8];
  float celsius;

  if ( !ds.search(addr)) {
    ds.reset_search();
    delay(250);
    return;
  }

  Serial.println();

  // the first ROM byte indicates which chip
  switch (addr[0]) {
    case 0x10:
      Serial.println("  Chip = DS18S20");  // or old DS1820
      type_s = 1;
      break;
    case 0x28:
      Serial.println("  Chip = DS18B20");
      type_s = 0;
      break;
    case 0x22:
      Serial.println("  Chip = DS1822");
      type_s = 0;
      break;
    default:
      Serial.println("Device is not a DS18x20 family device.");
      return;
  } 

  ds.reset();
  ds.select(addr);
  ds.write(0x44, 1);        // start conversion, with parasite power on at the end

  delay(850);     // maybe 750ms is enough, maybe not
  // we might do a ds.depower() here, but the reset will take care of it.

  present = ds.reset();
  ds.select(addr);    
  ds.write(0xBE);         // Read Scratchpad

  Serial.print("  Data = ");
  Serial.print(present, HEX);
  Serial.print(" ");
  for ( i = 0; i &lt; 9; i++) {           // we need 9 bytes
    data[i] = ds.read();
    Serial.print(data[i], HEX);
    Serial.print(" ");
  }
  Serial.print(" CRC=");
  Serial.print(OneWire::crc8(data, 8), HEX);
  Serial.println();

  // Convert the data to actual temperature
  // because the result is a 16 bit signed integer, it should
  // be stored to an "int16_t" type, which is always 16 bits
  // even when compiled on a 32 bit processor.
  int16_t raw = (data[1] &lt;&lt; 8) | data[0];
  if (type_s) {
    raw = raw &lt;&lt; 3; // 9 bit resolution default
    if (data[7] == 0x10) {
      // "count remain" gives full 12 bit resolution
      raw = (raw &amp; 0xFFF0) + 12 - data[6];
    }
  } else {
    byte cfg = (data[4] &amp; 0x60);
    // at lower res, the low bits are undefined, so let's zero them
    if (cfg == 0x00) raw = raw &amp; ~7;  // 9 bit resolution, 93.75 ms
    else if (cfg == 0x20) raw = raw &amp; ~3; // 10 bit res, 187.5 ms
    else if (cfg == 0x40) raw = raw &amp; ~1; // 11 bit res, 375 ms
    //// default is 12 bit resolution, 750 ms conversion time
  }
  celsius = (float)raw / 16.0;


  digitalWrite(3, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(10);              // wait for a second
  digitalWrite(3, LOW);    // turn the LED off by making the voltage LOW


   lcd.home ();
   lcd.print("Reading 1");
   lcd.setCursor( 0, 1);
   lcd.print("temp:");
   lcd.print(celsius);
   lcd.print("*C");

   if (celsius &gt;= 25 &amp;&amp; celsius &lt; 30) {
    digitalWrite(4,HIGH);
   } else if (celsius &gt;= 30) {
blink1();
   } else {
    digitalWrite(4,LOW);
   }

}

void blink1() {
digitalWrite(4,HIGH);
delay(50);
digitalWrite(4,LOW);
}
</code></pre>
 20208: <p>Here try this:</p>

<pre><code>#include &lt;OneWire.h&gt;

#include &lt;Wire.h&gt; 
#include &lt;LiquidCrystal_I2C.h&gt;



LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  // Set the LCD I2C address

//LiquidCrystal_I2C lcd(0x27, POSITIVE);  // Set the LCD I2C address
OneWire  ds(2);

const long interval = 1000; //İnterval at which to blink(milliseconds)
unsigned long previousMillis = 0;
int ledState = LOW;
void setup()
{
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);

  lcd.begin(16,2);               // initialize the lcd 

}

void loop()
{

  byte i;
  byte present = 0;
  byte type_s;
  byte data[12];
  byte addr[8];
  float celsius;

  if ( !ds.search(addr)) {
    ds.reset_search();
    delay(250);
    return;
  }

  Serial.println();

  // the first ROM byte indicates which chip
  switch (addr[0]) {
    case 0x10:
      Serial.println("  Chip = DS18S20");  // or old DS1820
      type_s = 1;
      break;
    case 0x28:
      Serial.println("  Chip = DS18B20");
      type_s = 0;
      break;
    case 0x22:
      Serial.println("  Chip = DS1822");
      type_s = 0;
      break;
    default:
      Serial.println("Device is not a DS18x20 family device.");
      return;
  } 

  ds.reset();
  ds.select(addr);
  ds.write(0x44, 1);        // start conversion, with parasite power on at the end

  delay(850);     // maybe 750ms is enough, maybe not
  // we might do a ds.depower() here, but the reset will take care of it.

  present = ds.reset();
  ds.select(addr);    
  ds.write(0xBE);         // Read Scratchpad

  Serial.print("  Data = ");
  Serial.print(present, HEX);
  Serial.print(" ");
  for ( i = 0; i &lt; 9; i++) {           // we need 9 bytes
    data[i] = ds.read();
    Serial.print(data[i], HEX);
    Serial.print(" ");
  }
  Serial.print(" CRC=");
  Serial.print(OneWire::crc8(data, 8), HEX);
  Serial.println();

  // Convert the data to actual temperature
  // because the result is a 16 bit signed integer, it should
  // be stored to an "int16_t" type, which is always 16 bits
  // even when compiled on a 32 bit processor.
  int16_t raw = (data[1] &lt;&lt; 8) | data[0];
  if (type_s) {
    raw = raw &lt;&lt; 3; // 9 bit resolution default
    if (data[7] == 0x10) {
      // "count remain" gives full 12 bit resolution
      raw = (raw &amp; 0xFFF0) + 12 - data[6];
    }
  } else {
    byte cfg = (data[4] &amp; 0x60);
    // at lower res, the low bits are undefined, so let's zero them
    if (cfg == 0x00) raw = raw &amp; ~7;  // 9 bit resolution, 93.75 ms
    else if (cfg == 0x20) raw = raw &amp; ~3; // 10 bit res, 187.5 ms
    else if (cfg == 0x40) raw = raw &amp; ~1; // 11 bit res, 375 ms
    //// default is 12 bit resolution, 750 ms conversion time
  }
  celsius = (float)raw / 16.0;

   lcd.home ();
   lcd.print("Reading 1");
   lcd.setCursor( 0, 1);
   lcd.print("temp:");
   lcd.print(celsius);
   lcd.print("*C");

   if (celsius &gt;= 25 &amp;&amp; celsius &lt; 30) {
    digitalWrite(4,HIGH);
   } else if (celsius &gt;= 30) {
blink1();
   } else {
    digitalWrite(4,LOW);
   }

   unsigned long currentMillis = millis();

   if (currentMillis - previousMillis &gt;= interval) {

     previousMillis = currentMillis;

     if (ledState == LOW) {
       ledState = HIGH;
     } else {
       ledState = LOW;
     }

     digitalWrite(3, ledState);
   }
}

void blink1() {
digitalWrite(4,HIGH);
delay(50);
digitalWrite(4,LOW);
}
</code></pre>

<p>and also note that i choosed 1000 milliseconds for interval (equal to 1 second) so if you want 10ms as in your first post then change <code>const long interval</code> to 10</p>
