user16572: Short version: 
I have a program that connects my ESP8266 to WIFI so I can control a relay connected to it over the internet or a button. I also have a sensor for my door. This software works perfectly, if I add a light dependent resistor to it (which is connected correctly since I do get readings from it) and start reading data I lose my WIFI connection. Has anyone got any idea why this is happening?
Long version: 
So I have this program running on my Esp8266

#include <ESP8266WiFi.h>

IPAddress ip(192, 168, 0, 150);
IPAddress gateway(192, 168, 0, 1);
IPAddress subnet(255, 255, 255, 0);

const char* ssid = "mySSID";
const char* password = "myPSW";
const char* host = "192.168.0.228";

const int buttonPin = 0;
const int relayPin =  4;
const int doorPin = 5;
const int ldrPin = A0;


//int ldrState;
//int serialCount = 0;
//int ldrMin = 0;
//int ldrMax = 1024;
int buttonState = 0;
int doorState = 0;
byte Main_Light_State_Begin;
bool Main_Light_State;
bool doorNotified = false;
bool button_action_taken = false;
bool Main_Light_DBR = true;
String HTTP_Get_Response;

WiFiServer server(80);

//Functions
String HTTP_Get(char* Adress, String URL, bool Last_Line_Bool) {
  WiFiClient client;
  const int httpPort = 80;
  if (!client.connect(Adress, httpPort)) {
    Serial.println("connection failed");
    return "Failed";
  }

  Serial.print("Requesting URL: ");
  Serial.println(URL);
  Serial.println("at adress");
  Serial.println(Adress);
  client.print(String("GET ") + URL + " HTTP/1.1\r\n" +
               "Host: " + Adress + "\r\n" +
               "Connection: close\r\n\r\n");
  delay(10);

  String Response;
  String Last_Line;

  while (client.available()) {
    String line = client.readStringUntil('\r');
    Serial.print(line);
    Response = Response + line;
  }
  return Response;

  Serial.println();
  Serial.println("closing connection");

}

void setup() {
  Serial.begin(115200);
  delay(1000);

  Serial.println();
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);



  WiFi.begin(ssid, password);
  WiFi.config(ip, gateway, subnet);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.println("WiFi connected");

  server.begin(); -
  Serial.println("Server started");

  Serial.println(WiFi.localIP());
  pinMode(relayPin, OUTPUT);
  pinMode(buttonPin, INPUT);
  pinMode(doorPin, INPUT);
//  pinMode(ldrPin, INPUT);
}

void loop() {
  if (WiFi.status() != WL_CONNECTED) {
    Serial.println("Wifi NOT Connected");
  }
  //Sensors
  buttonState = digitalRead(buttonPin);
  doorState = digitalRead(doorPin);
  //ldrState = map(analogRead(ldrPin), ldrMin, ldrMax, 0, 100);
  //Serial.println(analogRead(ldrPin));
//  if (serialCount == 1000) {
//    Serial.println(ldrState);
//    serialCount = 0;
//  } else {
//    serialCount ++;
//  }

  //Doorsensor
  if (doorState == HIGH) {
    if (doorNotified == false) {
      Serial.println("DOOR");
      HTTP_Get_Response = HTTP_Get("192.168.0.228", "/index.php/?door_opened=true", false);
      doorNotified = true;
    }
  } else if (doorState == LOW) {
    if (doorNotified == true) {
      doorNotified = false;
      delay(500);
    }
    else {
      doorNotified = false;
    }
  }

  //Button
  if (buttonState == LOW) {
    if (button_action_taken == false) {
      if (Main_Light_State == true) {
        Serial.println("SWITCH");
        Main_Light_State = false;
        digitalWrite(relayPin, HIGH);
        delay(500);
        Main_Light_DBR = false;
      }
      else if (Main_Light_State == false) {
        Serial.println("SWITCH");
        Main_Light_State = true;
        digitalWrite(relayPin, LOW);
        delay(500);
        Main_Light_DBR = false;
      }
      button_action_taken = true;
    }
  } else if (buttonState == HIGH) {
    if (button_action_taken == true) {
      button_action_taken = false;
      delay(500);
    }
    else {
      button_action_taken = false;
    }

  }
  //Main_Light_State
  if (Main_Light_State == true) {
    digitalWrite(relayPin, LOW);
    if (Main_Light_DBR == false) {
      HTTP_Get_Response = HTTP_Get("192.168.0.228", "/index.php/?main_light_on_dbr=true", false);
      Main_Light_DBR = true;
    }

  } else if (Main_Light_State == false) {
    digitalWrite(relayPin, HIGH);
    if (Main_Light_DBR == false) {
      HTTP_Get_Response = HTTP_Get("192.168.0.228", "/index.php/?main_light_off_dbr=true", false);
      Main_Light_DBR = true;
    }
  }

  WiFiClient client = server.available();
  if (!client) {
    return;
  }

  Serial.println("new client");
  while (!client.available()) {
    delay(1);
  }

  String req = client.readStringUntil('\r');
  Serial.println(req);
  client.flush();

  if (req.indexOf("/main_light/on") != -1) {
    Main_Light_State = true;
    Main_Light_DBR = false;
  } else if (req.indexOf("/main_light/off") != -1) {
    Main_Light_State = false;
    Main_Light_DBR = false;
  } else if (req.indexOf("/main_light/switch") != -1) {
    Serial.println("SWITCH");
    if (Main_Light_State == true) {
      Main_Light_State = false;
    }
    else if (Main_Light_State == false) {
      Main_Light_State = true;
    }
    Main_Light_DBR = false;
  } else if (req.indexOf("/main_light/state") != -1) {

  } else {
    Serial.println("invalid request");
    client.stop();
    return;
  }

  client.flush();

  String s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n";
  s += (Main_Light_State) ? "1" : "0";

  client.print(s);
  delay(1);
  Serial.println("Client disonnected");
}

With the lines I commented like above everything works fine. I have a light dependant resistor connected (correctly, I get correct measurements from it) to A0. From the moment on I uncomment the lines involving this LDR and thus start reading data from it I lose my wifi connection. Has anyone got any idea why this is? Thank you!

user38988: Here is what I usually do to give repetition at fixed intervals: 
void readAnalogSensor(){
  if (millis()<taskTime) return; // time is not expired yet
  taskTime += 50; // set time for the following execution
  // .... more code for the task that is done every 50 ms
}

This requires an unsigned long variable taskTime. You may also use a constant instead of the 50.
taskTime should be set to some value close to millis() at the end of setup(), otherwise there will be a rapid sequence of executions while taskTime catches up with millis(). 

user33836: This is an old question that has been answered, but I would like to offer a slightly more elegant solution (IMO!):
In my method which reads the analog data, I check and only read every 50 milliseconds:
void readAnalogSensor() {
   if( millis() % 50 != 0 )
       return;
   .
   .  // Do your sensor read and processing here
   .
}

This avoids having to keep a loop count and seems more deterministic - the loop count value will not necessarily increase in a consistent fashion depending on what else is going on in the loop.  Having the millis values available is also useful if you need to implement some button debounce code.

user16572: I have found that this was caused by reading the analog pin to many times in a short period of time. I replaced 
  ldrState = map(analogRead(ldrPin), ldrMin, ldrMax, 0, 100);
  Serial.println(analogRead(ldrPin));
  if (serialCount == 1000) {
    Serial.println(ldrState);
    serialCount = 0;
  } else {
    serialCount ++;
  }

with this:
if (serialCount == 10000) {
  ldrState = map(analogRead(ldrPin), ldrMin, ldrMax, 0, 100);
  Serial.println(ldrState);
  serialCount = 0;
} else {
  serialCount ++;
}

Although I thought of this approach before, my mistake was that I was still reading the sensor every time the code loops, I just wasn't printing it to the serial monitor until each 100th loop. 
This still gives me a reading several times per second, which is way more then I need. Anyway, now I know that I can't read my ESP8266 Analog pin to many times per second or the wifi will disconnect (at least when using it with the Arduino IDE)

16572: <p>Short version: 
I have a program that connects my ESP8266 to WIFI so I can control a relay connected to it over the internet or a button. I also have a sensor for my door. This software works perfectly, if I add a light dependent resistor to it (which is connected correctly since I do get readings from it) and start reading data I lose my WIFI connection. Has anyone got any idea why this is happening?</p>

<p>Long version: </p>

<p>So I have this program running on my Esp8266
</p>

<pre class="lang-cpp prettyprint-override"><code>#include &lt;ESP8266WiFi.h&gt;

IPAddress ip(192, 168, 0, 150);
IPAddress gateway(192, 168, 0, 1);
IPAddress subnet(255, 255, 255, 0);

const char* ssid = "mySSID";
const char* password = "myPSW";
const char* host = "192.168.0.228";

const int buttonPin = 0;
const int relayPin =  4;
const int doorPin = 5;
const int ldrPin = A0;


//int ldrState;
//int serialCount = 0;
//int ldrMin = 0;
//int ldrMax = 1024;
int buttonState = 0;
int doorState = 0;
byte Main_Light_State_Begin;
bool Main_Light_State;
bool doorNotified = false;
bool button_action_taken = false;
bool Main_Light_DBR = true;
String HTTP_Get_Response;

WiFiServer server(80);

//Functions
String HTTP_Get(char* Adress, String URL, bool Last_Line_Bool) {
  WiFiClient client;
  const int httpPort = 80;
  if (!client.connect(Adress, httpPort)) {
    Serial.println("connection failed");
    return "Failed";
  }

  Serial.print("Requesting URL: ");
  Serial.println(URL);
  Serial.println("at adress");
  Serial.println(Adress);
  client.print(String("GET ") + URL + " HTTP/1.1\r\n" +
               "Host: " + Adress + "\r\n" +
               "Connection: close\r\n\r\n");
  delay(10);

  String Response;
  String Last_Line;

  while (client.available()) {
    String line = client.readStringUntil('\r');
    Serial.print(line);
    Response = Response + line;
  }
  return Response;

  Serial.println();
  Serial.println("closing connection");

}

void setup() {
  Serial.begin(115200);
  delay(1000);

  Serial.println();
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);



  WiFi.begin(ssid, password);
  WiFi.config(ip, gateway, subnet);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.println("WiFi connected");

  server.begin(); -
  Serial.println("Server started");

  Serial.println(WiFi.localIP());
  pinMode(relayPin, OUTPUT);
  pinMode(buttonPin, INPUT);
  pinMode(doorPin, INPUT);
//  pinMode(ldrPin, INPUT);
}

void loop() {
  if (WiFi.status() != WL_CONNECTED) {
    Serial.println("Wifi NOT Connected");
  }
  //Sensors
  buttonState = digitalRead(buttonPin);
  doorState = digitalRead(doorPin);
  //ldrState = map(analogRead(ldrPin), ldrMin, ldrMax, 0, 100);
  //Serial.println(analogRead(ldrPin));
//  if (serialCount == 1000) {
//    Serial.println(ldrState);
//    serialCount = 0;
//  } else {
//    serialCount ++;
//  }

  //Doorsensor
  if (doorState == HIGH) {
    if (doorNotified == false) {
      Serial.println("DOOR");
      HTTP_Get_Response = HTTP_Get("192.168.0.228", "/index.php/?door_opened=true", false);
      doorNotified = true;
    }
  } else if (doorState == LOW) {
    if (doorNotified == true) {
      doorNotified = false;
      delay(500);
    }
    else {
      doorNotified = false;
    }
  }

  //Button
  if (buttonState == LOW) {
    if (button_action_taken == false) {
      if (Main_Light_State == true) {
        Serial.println("SWITCH");
        Main_Light_State = false;
        digitalWrite(relayPin, HIGH);
        delay(500);
        Main_Light_DBR = false;
      }
      else if (Main_Light_State == false) {
        Serial.println("SWITCH");
        Main_Light_State = true;
        digitalWrite(relayPin, LOW);
        delay(500);
        Main_Light_DBR = false;
      }
      button_action_taken = true;
    }
  } else if (buttonState == HIGH) {
    if (button_action_taken == true) {
      button_action_taken = false;
      delay(500);
    }
    else {
      button_action_taken = false;
    }

  }
  //Main_Light_State
  if (Main_Light_State == true) {
    digitalWrite(relayPin, LOW);
    if (Main_Light_DBR == false) {
      HTTP_Get_Response = HTTP_Get("192.168.0.228", "/index.php/?main_light_on_dbr=true", false);
      Main_Light_DBR = true;
    }

  } else if (Main_Light_State == false) {
    digitalWrite(relayPin, HIGH);
    if (Main_Light_DBR == false) {
      HTTP_Get_Response = HTTP_Get("192.168.0.228", "/index.php/?main_light_off_dbr=true", false);
      Main_Light_DBR = true;
    }
  }

  WiFiClient client = server.available();
  if (!client) {
    return;
  }

  Serial.println("new client");
  while (!client.available()) {
    delay(1);
  }

  String req = client.readStringUntil('\r');
  Serial.println(req);
  client.flush();

  if (req.indexOf("/main_light/on") != -1) {
    Main_Light_State = true;
    Main_Light_DBR = false;
  } else if (req.indexOf("/main_light/off") != -1) {
    Main_Light_State = false;
    Main_Light_DBR = false;
  } else if (req.indexOf("/main_light/switch") != -1) {
    Serial.println("SWITCH");
    if (Main_Light_State == true) {
      Main_Light_State = false;
    }
    else if (Main_Light_State == false) {
      Main_Light_State = true;
    }
    Main_Light_DBR = false;
  } else if (req.indexOf("/main_light/state") != -1) {

  } else {
    Serial.println("invalid request");
    client.stop();
    return;
  }

  client.flush();

  String s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n";
  s += (Main_Light_State) ? "1" : "0";

  client.print(s);
  delay(1);
  Serial.println("Client disonnected");
}
</code></pre>

<p>With the lines I commented like above everything works fine. I have a light dependant resistor connected (correctly, I get correct measurements from it) to A0. From the moment on I uncomment the lines involving this LDR and thus start reading data from it I lose my wifi connection. Has anyone got any idea why this is? Thank you!</p>
 38988: <p>Here is what I usually do to give repetition at fixed intervals: </p>

<pre><code>void readAnalogSensor(){
  if (millis()&lt;taskTime) return; // time is not expired yet
  taskTime += 50; // set time for the following execution
  // .... more code for the task that is done every 50 ms
}
</code></pre>

<p>This requires an <code>unsigned long variable taskTime</code>. You may also use a constant instead of the 50.<br>
<code>taskTime</code> should be set to some value close to <code>millis()</code> at the end of <code>setup()</code>, otherwise there will be a rapid sequence of executions while <code>taskTime</code> catches up with <code>millis()</code>. </p>
 33836: <p>This is an old question that has been answered, but I would like to offer a slightly more elegant solution (IMO!):</p>

<p>In my method which reads the analog data, I check and only read every 50 milliseconds:</p>

<pre><code>void readAnalogSensor() {
   if( millis() % 50 != 0 )
       return;
   .
   .  // Do your sensor read and processing here
   .
}
</code></pre>

<p>This avoids having to keep a loop count and seems more deterministic - the loop count value will not necessarily increase in a consistent fashion depending on what else is going on in the loop.  Having the millis values available is also useful if you need to implement some button debounce code.</p>
 16572: <p>I have found that this was caused by reading the analog pin to many times in a short period of time. I replaced </p>

<pre><code>  ldrState = map(analogRead(ldrPin), ldrMin, ldrMax, 0, 100);
  Serial.println(analogRead(ldrPin));
  if (serialCount == 1000) {
    Serial.println(ldrState);
    serialCount = 0;
  } else {
    serialCount ++;
  }
</code></pre>

<p>with this:</p>

<pre><code>if (serialCount == 10000) {
  ldrState = map(analogRead(ldrPin), ldrMin, ldrMax, 0, 100);
  Serial.println(ldrState);
  serialCount = 0;
} else {
  serialCount ++;
}
</code></pre>

<p>Although I thought of this approach before, my mistake was that I was still reading the sensor every time the code loops, I just wasn't printing it to the serial monitor until each 100th loop. </p>

<p>This still gives me a reading several times per second, which is way more then I need. Anyway, now I know that I can't read my ESP8266 Analog pin to many times per second or the wifi will disconnect (at least when using it with the Arduino IDE)</p>
