How can I loop my code? For example after 30 minutes?

Question

So I have this code which records the temperature and humidity using a DHT22 sensor. After it get's the values it then sends it to a webpage using PHP $_GET method, where that gets imported into a DB and emails (using PHP). But this only happens when I upload the code to my ESP8266; how can I know build in a loop function that it sends it every 30 mins or given time?

#include <ESP8266WiFi.h>
#include "DHT.h"

const char* ssid     = "bbox2";      // SSID of local network
const char* password = "azerty";   // Password on network

WiFiClient client;
char servername[]="lucasdebelder.be";  // remote server we will connect to
String result;

float temperature;
float humidity;

#define DHTPIN 14  

#define DHTTYPE DHT22 
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  dht.begin();
  delay(2000);
  Serial.begin(115200);
  Serial.println("Connecting");
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(100);
  }
  Serial.println("Connected");
  delay(1000);
  readSensor();
  String temperatureString = String(temperature,1);
  String humidityString = String(humidity,1);
  sendDataToServer(temperatureString,humidityString);
}

void loop() {

}

void sendDataToServer(String temperature, String humidity)
{
  if (client.connect(servername, 80)) {  //starts client connection, checks for connection
    Serial.println("connected");
    client.println("GET /send_temperature.php?temperature="+temperature+"&humidity="+humidity+" HTTP/1.1"); //Send data
    client.println("Host: lucasdebelder.be");
    client.println("Connection: close");  //close 1.1 persistent connection  
    client.println(); //end of get request
  } 
  else {
    Serial.println("connection failed"); //error message if no client connect
    Serial.println();
  }

 while(client.connected() && !client.available()) delay(1); //waits for data
  while (client.connected() || client.available()) { //connected or data available
    char c = client.read(); //gets byte from ethernet buffer
      result = result+c;
    }

  client.stop(); //stop client
  Serial.println(result);

}


void readSensor()
{

  humidity = dht.readHumidity();
  temperature = dht.readTemperature();
  Serial.println("Temperature:");
  Serial.println(temperature);
  Serial.println("Humidity:");
  Serial.println(humidity);

}

Answer 1

As stated in the previous answer. Code that needs to run more than one time should be called in the loop. But in this case the following solution will work as well.

You can end your setup with a call to the deepsleep(time_us) function which can be found in the ESP library. This will shutdown everything except for the on board RTC(Real Time Clock). So the circuit only draws a very little current (20 uA). This can be very useful if the circuit is powered by a battery.

The RTC has a signal on GPIO 16 (D0 on NodeMcu) which will be held HIGH while the given time is not reached. If the given time is reached the signal will be LOW.

If you connect GPIO 16 to the RST(reset) pin, this will make the ESP8266 start-up again. And thus the setup() will be executed again.

Answer 2

You execute the corresponding function only in the setup() function, which is called once on startup of the ESP. After that the loop() function is called repeatedly. The setup() function is meant to "setup" your code for it's functionality, which is then executed in the loop() function. For example you are begin the Wifi connection and connect to a network in there, because you need the network for your main functionality.

So you have to put the code from readSensor() until (and including) sendDataToServer() into the loop() function. This will execute this code repeatedly.

Then you have to introduce some concept of time, else your code will be executed very fast, effectively flooding your webserver. The easiest way would be to add a call to delay(30000), which would delay the code for 30s. But using delay is not considered good coding style, since it is basically busy waiting and you cannot do anything else during that time.

So to be able to add other functionalities in the future you can implement the time concept with non-blocking code. Take the BlinkWithoutDelay example from the Arduino IDE as reference. It uses the millis() function, which counts the milliseconds since the startup. You save a timestamp of the last execution of your code and wait until the difference between the current time (given by millis()) and your timestamp is greater than 30s. In this time the ESP can do other things, since it still goes through the loop() function undisrupted. Then after the timespan you execute the code and reset the timestamp to the current time.