WeMosをRESPのクライアントとして機能するため、JSONと、HTTPClientを検証する。

前回ArduinoJsonというライブラリを使用したので、ESP8266ならではのWiFi機能を使い、インターネットから情報を取得して表示させてみる。

JSON データ形式

為替レートの情報は、

Foreign exchange rates and currency conversion JSON API

から取得する。

ドル円レートの情報を取得する場合、URLはhttp://api.fixer.io/latest?base=USD&symbols=JPY


応答は下記の通り

HTTP/1.1 200 OK
Server: nginx/1.13.6
Date: Sat, 04 Nov 2017 13:40:46 GMT
Content-Type: application/json
Content-Length: 57
Connection: close
Cache-Control: public, must-revalidate, max-age=900
Last-Modified: Fri, 03 Nov 2017 00:00:00 GMT
Vary: Origin
X-Content-Type-Options: nosniff
{"base":"USD","date":"2017-11-03","rates":{"JPY":113.94}}

closing connection

プログラム

下記の処理をする

1.  WiFiManagerでWiFi自動接続
2. get_exchange_rate処理
   1. api.fixer.io　JSONデータ取得
   2. parse json data
   3. OLEDへ表示
3. 60秒待ち
4. ２へ続き

#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>
#include <ArduinoJson.h>

#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
 
#define OLED_RESET 0  // GPIO0
Adafruit_SSD1306 OLED(OLED_RESET);

const char* URL = "http://api.fixer.io/latest?base=USD&symbols=JPY";  // http resource
//sample json data used in this sketch
// {"base":"USD","date":"2017-11-03","rates":{"JPY":113.94}}

//needed for library
#include <DNSServer.h>
#include <ESP8266WebServer.h>
#include "WiFiManager.h"          //https://github.com/tzapu/WiFiManager

void configModeCallback (WiFiManager *myWiFiManager) {
  Serial.println("Entered config mode");
  Serial.println(WiFi.softAPIP());
  //if you used auto generated SSID, print it
  Serial.println(myWiFiManager->getConfigPortalSSID());
}

void setup() {
  OLED.begin();
  OLED.clearDisplay();
 
  //Add stuff into the 'display buffer'
  OLED.setTextWrap(false);
  OLED.setTextSize(1);
  OLED.setTextColor(WHITE);
  OLED.setCursor(0,0);
  delay(10);
  
  Serial.begin(115200);
  Serial.println("");
  delay(10);

  // Connect to WiFi network
  OLED.println("wifiManager autoConnect...");
  OLED.display(); //output 'display buffer' to screen  
 
  //WiFiManager
  //Local intialization. Once its business is done, there is no need to keep it around
  WiFiManager wifiManager;
  //reset settings - for testing
  //wifiManager.resetSettings();

  //set callback that gets called when connecting to previous WiFi fails, and enters Access Point mode
  wifiManager.setAPCallback(configModeCallback);

  //fetches ssid and pass and tries to connect
  //if it does not connect it starts an access point with the specified name
  //here  "AutoConnectAP"
  //and goes into a blocking loop awaiting configuration
  if(!wifiManager.autoConnect()) {
    Serial.println("failed to connect and hit timeout");
    //reset and try again, or maybe put it to deep sleep
    ESP.reset();
    delay(1000);
  } 

  // Print the IP address
  OLED.print("http://");
  OLED.print(WiFi.localIP());
  OLED.println("/");
  OLED.println("WiFi connected");
  OLED.display(); //output 'display buffer' to screen  
  
  //if you get here you have connected to the WiFi
  Serial.println("connected...yeey :)");
 
}

void get_exchange_rate() {
  const int BUFFER_SIZE = JSON_OBJECT_SIZE(4) + JSON_ARRAY_SIZE(1);
  StaticJsonBuffer<BUFFER_SIZE> jsonBuffer;
  HTTPClient http;

  Serial.print("[HTTP] begin...\n");
  // configure targed server and url
  http.begin(URL);
  
  Serial.print("[HTTP] GET...\n");
  // start connection and send HTTP header
  int httpCode = http.GET();

  if(httpCode != HTTP_CODE_OK) {
    return;
  }
  String buffer = http.getString();
  Serial.println(buffer);

  //parse json data
  char json[buffer.length() + 1];
  buffer.toCharArray(json, sizeof(json));
  Serial.println(json);
  JsonObject& root = jsonBuffer.parseObject(json);
  if (!root.success()) {
    Serial.println("parseObject() failed");
    return;
  }
  const char* date = root["date"];
  Serial.println(date);
  const char* base = root["base"];
  Serial.println(base);
  JsonObject& rates = root["rates"];
  rates.printTo(Serial);
  Serial.println();
  const char* rate = rates["JPY"];
  Serial.println(rate);
  Serial.println();
  
  Serial.println("closing connection");

  OLED.clearDisplay();
  OLED.setCursor(0,0);
  // Print the IP address
  OLED.print("http://");
  OLED.print(WiFi.localIP());
  OLED.println("/");

  OLED.setCursor(0, 16);
  OLED.print(date);
  OLED.setCursor(0, 24);
  OLED.print("JPY/");
  OLED.print(base);
  OLED.print(": ");
  OLED.print(rate);
  OLED.display(); //output 'display buffer' to screen  

}

void loop() {
  get_exchange_rate();
  delay(60000);
}

 

参考

• http://blog.boochow.com/article/425016458.html — ESP8266版Arduinoでネットから情報を取ってきてLCDに表示する