• Persistent storage of volume and station index
• Visualization of selected station, volume and wifi signal strength (RSSI)
• Auto-recovery in case of remote failure
• Auto-configuration: Wifi connection is started by pushing WPS on Wifi Access Point

• ESP32 module with OLED display (e.g. Wemos Lolin board)
• MAX98357 audio I2S power amp
• 2 Watt 8 ohm audio speaker

• Connect 5V(ESP32+OLED) together with VIN(MAX98357)
• Connect GND(ESP32+OLED) together with GND(MAX98357)
• Connect GPIO 16(ESP32+OLED) together with LRC(MAX98357)
• Connect GPIO 14(ESP32+OLED) together with BCLK(MAX98357)
• Connect GPIO 13(ESP32+OLED) together with DIN(MAX98357)
• Connect audio speaker to MAX98357 output
• Connect push button to GPIO(ESP32+OLED) defined as Pin_previous, Pin_next, Pin_vol_up, Pin_vol_down

#include "Audio.h"
#include "SSD1306Wire.h"
#include "EEPROM.h"
#include "esp_wps.h"

void loop() {
  audio.loop();

  audiotime = audio.getAudioCurrentTime();

  //Display refresh logic
  if (millis() - refresh_time > 1000) {
      refresh_time = millis();
      display_music();
  }

  //Button logic
  int reading_previous = digitalRead(Pin_previous);
  if (reading_previous != lastButtonState[pb_previous]) {
    // reset the debouncing timer
    lastDebounceTime[pb_previous] = millis();
  }     
  if ((millis() - lastDebounceTime[pb_previous]) > debounceDelay) {
    if (reading_previous != buttonState[pb_previous]) {
      buttonState[pb_previous] = reading_previous;
      if (buttonState[pb_previous] == LOW) {
            Serial.println("Pin_previous");
            if (station_index > 0) {
                station_index--;
            } else {
                station_index = station_count - 1;
            }
            EEPROM.write(1, station_index);//save station index in EEPROM
            EEPROM.commit();            
            open_new_radio(stations[station_index]);
      }
    }
  }
  lastButtonState[pb_previous] = reading_previous;

  int reading_next = digitalRead(Pin_next);
  if (reading_next != lastButtonState[pb_next]) {
    // reset the debouncing timer
    lastDebounceTime[pb_next] = millis();
  }     
  if ((millis() - lastDebounceTime[pb_next]) > debounceDelay) {
    if (reading_next != buttonState[pb_next]) {
      buttonState[pb_next] = reading_next;
      if (buttonState[pb_next] == LOW) {
            Serial.println("Pin_next");
            if (station_index < station_count - 1) {
                station_index++;
            } else {
                station_index = 0;
            }
            EEPROM.write(1, station_index);//save station index in EEPROM
            EEPROM.commit();            
            open_new_radio(stations[station_index]);
      }
    }
  }
  lastButtonState[pb_next] = reading_next;

  int reading_vol_up = digitalRead(Pin_vol_up);
  if (reading_vol_up != lastButtonState[pb_vol_up]) {
    // reset the debouncing timer
    lastDebounceTime[pb_vol_up] = millis();
  }     
  if ((millis() - lastDebounceTime[pb_vol_up]) > debounceDelay) {
    if (reading_vol_up != buttonState[pb_vol_up]) {
      buttonState[pb_vol_up] = reading_vol_up;
      if (buttonState[pb_vol_up] == LOW) {
            Serial.println("Pin_vol_up");
            if (volume < 21)
                volume++;
            EEPROM.write(0, volume);//save volume in EEPROM
            EEPROM.commit();            
            audio.setVolume(volume);
      }
    }
  }
  lastButtonState[pb_vol_up] = reading_vol_up;

  int reading_vol_down = digitalRead(Pin_vol_down);
  if (reading_vol_down != lastButtonState[pb_vol_down]) {
    // reset the debouncing timer
    lastDebounceTime[pb_vol_down] = millis();
  }     
  if ((millis() - lastDebounceTime[pb_vol_down]) > debounceDelay) {
    if (reading_vol_down != buttonState[pb_vol_down]) {
      buttonState[pb_vol_down] = reading_vol_down;
      if (buttonState[pb_vol_down] == LOW) {
            Serial.println("Pin_vol_down");
            if (volume > 0)
                volume--;
            EEPROM.write(0, volume);//save volume in EEPROM
            EEPROM.commit();            
            audio.setVolume(volume);
      }
    }
  }
  lastButtonState[pb_vol_down] = reading_vol_down;    

  //Serial logic
  if (Serial.available()) {
      String r = Serial.readString();
      r.trim();
      if (r.length() > 5) {
          audio.stopSong();
          open_new_radio(r);
      } else {
          audio.setVolume(r.toInt());
      }
  }

  if (!audio.isRunning()) {//recovery logic, e.g. wifi connection was lost
    Serial.println("restart due to recovery logic");
    ESP.restart();
  }  
  
}