Description

This example shows how to implement an HTTP server that sends a JSON document in the response.

It uses the Ethernet library, but you can easily adapt it for WiFi.

It sends the value of the analog and digital pins. The JSON document looks like the following:

{
  "analog": [0, 76, 123, 158, 192, 205],
  "digital": [1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0]
}

Source code

#include <ArduinoJson.h>
#include <Ethernet.h>
#include <SPI.h>

byte mac[] = {0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};
EthernetServer server(80);

void setup() {
  // Initialize serial port
  Serial.begin(9600);
  while (!Serial) continue;

  // Initialize Ethernet libary
  if (!Ethernet.begin(mac)) {
    Serial.println(F("Failed to initialize Ethernet library"));
    return;
  }

  // Start to listen
  server.begin();

  Serial.println(F("Server is ready."));
  Serial.print(F("Please connect to http://"));
  Serial.println(Ethernet.localIP());
}

void loop() {
  // Wait for an incomming connection
  EthernetClient client = server.available();

  // Do we have a client?
  if (!client) return;

  Serial.println(F("New client"));

  // Read the request (we ignore the content in this example)
  while (client.available()) client.read();

  // Allocate a temporary JsonDocument
  // Use arduinojson.org/v6/assistant to compute the capacity.
  StaticJsonDocument<500> doc;

  // Create the "analog" array
  JsonArray analogValues = doc.createNestedArray("analog");
  for (int pin = 0; pin < 6; pin++) {
    // Read the analog input
    int value = analogRead(pin);

    // Add the value at the end of the array
    analogValues.add(value);
  }

  // Create the "digital" array
  JsonArray digitalValues = doc.createNestedArray("digital");
  for (int pin = 0; pin < 14; pin++) {
    // Read the digital input
    int value = digitalRead(pin);

    // Add the value at the end of the array
    digitalValues.add(value);
  }

  Serial.print(F("Sending: "));
  serializeJson(doc, Serial);
  Serial.println();

  // Write response headers
  client.println(F("HTTP/1.0 200 OK"));
  client.println(F("Content-Type: application/json"));
  client.println(F("Connection: close"));
  client.print(F("Content-Length: "));
  client.println(measureJsonPretty(doc));
  client.println();

  // Write JSON document
  serializeJsonPretty(doc, client);

  // Disconnect
  client.stop();
}

Things used in this example

Classes

Functions

Libraries

Hardware

See also