user60819: #include <LiquidCrystal.h>

#include <SoftwareSerial.h>


float pulse = 0;

float temp = 0;


SoftwareSerial ser(9,10);


String apiKey = "U5AGYVQT5JRJPSDR";


//  Variables

int pulsePin = A0;                 // Pulse Sensor purple wire connected to analog pin 0

int blinkPin = 7           ;                // pin to blink led at each beat

int fadePin = 8;                  // pin to do fancy classy fading blink at each beat

int fadeRate = 0;                 // used to fade LED on with PWM on fadePin


LiquidCrystal lcd(13, 12, 6, 5, 4, 3);


// Volatile Variables, used in the interrupt service routine!

volatile int BPM;                   // int that holds raw Analog in 0. updated every 2mS

volatile int Signal;                // holds the incoming raw data

volatile int IBI = 600;             // int that holds the time interval between beats! Must be seeded! 

volatile boolean Pulse = false;     // "True" when User's live heartbeat is detected. "False" when not
 a "live beat". 

volatile boolean QS = false;        // becomes true when Arduoino finds a beat.


// Regards Serial OutPut  -- Set This Up to your needs

static boolean serialVisual = true;   // Set to 'false' by Default.  Re-set to 'true' to see Arduino 
Serial Monitor ASCII Visual Pulse 


volatile int rate[10];                      // array to hold last ten IBI values

volatile unsigned long sampleCounter = 0;          // used to determine pulse timing

volatile unsigned long lastBeatTime = 0;           // used to find IBI

volatile int P = 512;                      // used to find peak in pulse wave, seeded

volatile int T = 512;                     // used to find trough in pulse wave, seeded

volatile int thresh = 525;                // used to find instant moment of heart beat, seeded

volatile int amp = 100;                   // used to hold amplitude of pulse waveform, seeded

volatile boolean firstBeat = true;        // used to seed rate array so we startup with reasonable BPM

volatile boolean secondBeat = false;      // used to seed rate array so we startup with reasonable BPM


void setup()

{

  lcd.begin(16, 2);

  pinMode(blinkPin,OUTPUT);         // pin that will blink to your heartbeat!

  pinMode(fadePin,OUTPUT);          // pin that will fade to your heartbeat!

  Serial.begin(115200);             // we agree to talk fast!

  interruptSetup();                 // sets up to read Pulse Sensor signal every 2mS 

                                    // IF YOU ARE POWERING The Pulse Sensor AT VOLTAGE LESS THAN THE BOARD VOLTAGE, 

                                    // UN-COMMENT THE NEXT LINE AND APPLY THAT VOLTAGE TO THE A-REF PIN

                                    //   analogReference(EXTERNAL);   

  lcd.clear();

  lcd.setCursor(0,0);

  lcd.print("Engineers Garage");


  ser.begin(9600);


  ser.println("AT");

  delay(1000);

  ser.println("AT+GMR");

  delay(1000);

  ser.println("AT+CWMODE=3");

  delay(1000);

  ser.println("AT+RST");

  delay(5000);

  ser.println("AT+CIPMUX=1");

  delay(1000);

  String cmd="AT+CWJAP="EngineersGarage","egP@$$w0rd?"";

  ser.println(cmd);

  delay(1000);

  ser.println("AT+CIFSR");

  delay(1000);

}


//  Where the Magic Happens

void loop()

{

   serialOutput();  



  if (QS == true) // A Heartbeat Was Found

    {     

      // BPM and IBI have been Determined

      // Quantified Self "QS" true when arduino finds a heartbeat

      fadeRate = 255; // Makes the LED Fade Effect Happen, Set 'fadeRate' Variable to 255 to fade LED
 with pulse

      serialOutputWhenBeatHappens(); // A Beat Happened, Output that to serial.     

      QS = false; // reset the Quantified Self flag for next time    

    }



  ledFadeToBeat(); // Makes the LED Fade Effect Happen 

  delay(20); //  take a break


  read_temp();



  esp_8266();

}


void ledFadeToBeat()

{

   fadeRate -= 15;                         //  set LED fade value

   fadeRate = constrain(fadeRate,0,255);   //  keep LED fade value from going into negative numbers!

   analogWrite(fadePin,fadeRate);          //  fade LED

}


void interruptSetup()

{     

  // Initializes Timer2 to throw an interrupt every 2mS.

  TCCR2A = 0x02;     // DISABLE PWM ON DIGITAL PINS 3 AND 11, AND GO INTO CTC MODE

  TCCR2B = 0x06;     // DON'T FORCE COMPARE, 256 PRESCALER 

  OCR2A  = 0X7C;      // SET THE TOP OF THE COUNT TO 124 FOR 500Hz SAMPLE RATE

  TIMSK2 = 0x02;     // ENABLE INTERRUPT ON MATCH BETWEEN TIMER2 AND OCR2A

  sei();             // MAKE SURE GLOBAL INTERRUPTS ARE ENABLED      

} 


void serialOutput()

{   // Decide How To Output Serial. 

 if (serialVisual == true)

  {  

     arduinoSerialMonitorVisual('-', Signal);   // goes to function that makes Serial Monitor Visualizer

  } 

 else

  {

      sendDataToSerial('S', Signal);     // goes to sendDataToSerial function

   }        

}


void serialOutputWhenBeatHappens()

{    

 if (serialVisual == true) //  Code to Make the Serial Monitor Visualizer Work

   {            

     Serial.print("*** Heart-Beat Happened *** ");  //ASCII Art Madness

     Serial.print("BPM: ");

     Serial.println(BPM);

     lcd.clear();

     lcd.print("BPM: ");

     lcd.print(BPM);

   }

 else

   {

     sendDataToSerial('B',BPM);   // send heart rate with a 'B' prefix

     sendDataToSerial('Q',IBI);   // send time between beats with a 'Q' prefix

   }   

}


void arduinoSerialMonitorVisual(char symbol, int data )

{    

  const int sensorMin = 0;      // sensor minimum, discovered through experiment

  const int sensorMax = 1024;    // sensor maximum, discovered through experiment

  int sensorReading = data; // map the sensor range to a range of 12 options:

  int range = map(sensorReading, sensorMin, sensorMax, 0, 11);

  // do something different depending on the 

  // range value:

  switch (range) 

  {

    case 0:     

      Serial.println("");     /////ASCII Art Madness

      break;

    case 1:   

      Serial.println("---");

      break;

    case 2:    

      Serial.println("------");

      break;

    case 3:    

      Serial.println("---------");

      break;

    case 4:   

      Serial.println("------------");

      break;

    case 5:   

      Serial.println("--------------|-");

      break;

    case 6:   

      Serial.println("--------------|---");

      break;

    case 7:   

      Serial.println("--------------|-------");

      break;

    case 8:  

      Serial.println("--------------|----------");

      break;

    case 9:    

      Serial.println("--------------|----------------");

      break;

    case 10:   

      Serial.println("--------------|-------------------");

      break;

    case 11:   

      Serial.println("--------------|-----------------------");

      break;

  } 

}



void sendDataToSerial(char symbol, int data )

{

   Serial.print(symbol);

   Serial.println(data);                

}


ISR(TIMER2_COMPA_vect) //triggered when Timer2 counts to 124

{  

  cli();                                      // disable interrupts while we do this

  Signal = analogRead(pulsePin);              // read the Pulse Sensor 

  sampleCounter += 2;                         // keep track of the time in mS with this variable

  int N = sampleCounter - lastBeatTime;       // monitor the time since the last beat to avoid noise

                                              //  find the peak and trough of the pulse wave

  if(Signal < thresh && N > (IBI/5)*3) // avoid dichrotic noise by waiting 3/5 of last IBI

    {      

      if (Signal < T) // T is the trough

      {                        

        T = Signal; // keep track of lowest point in pulse wave 

      }

    }


  if(Signal > thresh && Signal > P)

    {          // thresh condition helps avoid noise

      P = Signal;                             // P is the peak

    }                                        // keep track of highest point in pulse wave


  //  NOW IT'S TIME TO LOOK FOR THE HEART BEAT

  // signal surges up in value every time there is a pulse

  if (N > 250)

  {                                   // avoid high frequency noise

    if ( (Signal > thresh) && (Pulse == false) && (N > (IBI/5)*3) )

      {        

        Pulse = true;                               // set the Pulse flag when we think there is a pulse

        digitalWrite(blinkPin,HIGH);                // turn on pin 13 LED

        IBI = sampleCounter - lastBeatTime;         // measure time between beats in mS

        lastBeatTime = sampleCounter;               // keep track of time for next pulse



        if(secondBeat)

        {                        // if this is the second beat, if secondBeat == TRUE

          secondBeat = false;                  // clear secondBeat flag

          for(int i=0; i<=9; i++) // seed the running total to get a realisitic BPM at startup

          {             

            rate[i] = IBI;                      

          }

        }



        if(firstBeat) // if it's the first time we found a beat, if firstBeat == TRUE

        {                         

          firstBeat = false;                   // clear firstBeat flag

          secondBeat = true;                   // set the second beat flag

          sei();                               // enable interrupts again

          return;                              // IBI value is unreliable so discard it

        }   

      // keep a running total of the last 10 IBI values

      word runningTotal = 0;                  // clear the runningTotal variable    


      for(int i=0; i<=8; i++)

        {                // shift data in the rate array

          rate[i] = rate[i+1];                  // and drop the oldest IBI value 

          runningTotal += rate[i];              // add up the 9 oldest IBI values

        }


      rate[9] = IBI;                          // add the latest IBI to the rate array

      runningTotal += rate[9];                // add the latest IBI to runningTotal

      runningTotal /= 10;                     // average the last 10 IBI values 

      BPM = 60000/runningTotal;               // how many beats can fit into a minute? that's BPM!

      QS = true;                              // set Quantified Self flag 

      // QS FLAG IS NOT CLEARED INSIDE THIS ISR

      pulse = BPM;

    }                       

  }


  if (Signal < thresh && Pulse == true)

    {   // when the values are going down, the beat is over

      digitalWrite(blinkPin,LOW);            // turn off pin 13 LED

      Pulse = false;                         // reset the Pulse flag so we can do it again

      amp = P - T;                           // get amplitude of the pulse wave

      thresh = amp/2 + T;                    // set thresh at 50% of the amplitude

      P = thresh;                            // reset these for next time

      T = thresh;

    }


  if (N > 2500)

    {                           // if 2.5 seconds go by without a beat

      thresh = 512;                          // set thresh default

      P = 512;                               // set P default

      T = 512;                               // set T default

      lastBeatTime = sampleCounter;          // bring the lastBeatTime up to date        

      firstBeat = true;                      // set these to avoid noise

      secondBeat = false;                    // when we get the heartbeat back

    }


  sei();                                   // enable interrupts when youre done!

}// end isr


void esp_8266()

{

   // TCP connection AT+CIPSTART=4,"TCP","184.106.153.149",80 

    String cmd = "AT+CIPSTART=4,"TCP","";

    cmd += "184.106.153.149"; // api.thingspeak.com

    cmd += "",80";

    ser.println(cmd);

    Serial.println(cmd); 

    if(ser.find("Error"))

    {

      Serial.println("AT+CIPSTART error");

      return;

    }

  // prepare GET string GET https://api.thingspeak.com/update?api_key=LHAG4NSIYJ5UWS6U&field1=0rnrn

  String getStr = "GET /update?api_key=";

  getStr += apiKey;

  getStr +="&field1=";

  getStr +=String(temp);

  getStr +="&field2=";

  getStr +=String(pulse);

  getStr += "rnrn";

  // send data length

  cmd = "AT+CIPSEND=4,";

  cmd += String(getStr.length());

  ser.println(cmd);

  Serial.println(cmd);

  delay(1000);

  ser.print(getStr);

  Serial.println(getStr);

 //thingspeak needs 15 sec delay between updates

  delay(3000);

}


void read_temp()

{

  int temp_val =  analogRead(A1);

  float mv = (temp_val/1024.0)*5000; 

  float cel = mv/10;

  temp = (cel*9)/5 + 32;

}


user37622: The sketch in the question is not for NodeMCU. It is for Arduino with esp8266 wired on pins 9 and 10. But the error in title is a current error for esp8266 Arduino boards package 2.6.0. The EspSoftwareSerial bundled with the esp8266 Arduino boards package version 2.6.0 has a compatibility breaking change.
The problem was immediately reported and the EspSoftwareSerial maintainer added the legacy API back to EspSoftwareSerial. The fixed version will be available with esp8266 boards package 2.6.1, which will be available soon because of multiple problems with 2.6.0. 

60819: <pre><code>#include &lt;LiquidCrystal.h&gt;

#include &lt;SoftwareSerial.h&gt;


float pulse = 0;

float temp = 0;


SoftwareSerial ser(9,10);


String apiKey = "U5AGYVQT5JRJPSDR";


//  Variables

int pulsePin = A0;                 // Pulse Sensor purple wire connected to analog pin 0

int blinkPin = 7           ;                // pin to blink led at each beat

int fadePin = 8;                  // pin to do fancy classy fading blink at each beat

int fadeRate = 0;                 // used to fade LED on with PWM on fadePin


LiquidCrystal lcd(13, 12, 6, 5, 4, 3);


// Volatile Variables, used in the interrupt service routine!

volatile int BPM;                   // int that holds raw Analog in 0. updated every 2mS

volatile int Signal;                // holds the incoming raw data

volatile int IBI = 600;             // int that holds the time interval between beats! Must be seeded! 

volatile boolean Pulse = false;     // "True" when User's live heartbeat is detected. "False" when not
 a "live beat". 

volatile boolean QS = false;        // becomes true when Arduoino finds a beat.


// Regards Serial OutPut  -- Set This Up to your needs

static boolean serialVisual = true;   // Set to 'false' by Default.  Re-set to 'true' to see Arduino 
Serial Monitor ASCII Visual Pulse 


volatile int rate[10];                      // array to hold last ten IBI values

volatile unsigned long sampleCounter = 0;          // used to determine pulse timing

volatile unsigned long lastBeatTime = 0;           // used to find IBI

volatile int P = 512;                      // used to find peak in pulse wave, seeded

volatile int T = 512;                     // used to find trough in pulse wave, seeded

volatile int thresh = 525;                // used to find instant moment of heart beat, seeded

volatile int amp = 100;                   // used to hold amplitude of pulse waveform, seeded

volatile boolean firstBeat = true;        // used to seed rate array so we startup with reasonable BPM

volatile boolean secondBeat = false;      // used to seed rate array so we startup with reasonable BPM


void setup()

{

  lcd.begin(16, 2);

  pinMode(blinkPin,OUTPUT);         // pin that will blink to your heartbeat!

  pinMode(fadePin,OUTPUT);          // pin that will fade to your heartbeat!

  Serial.begin(115200);             // we agree to talk fast!

  interruptSetup();                 // sets up to read Pulse Sensor signal every 2mS 

                                    // IF YOU ARE POWERING The Pulse Sensor AT VOLTAGE LESS THAN THE BOARD VOLTAGE, 

                                    // UN-COMMENT THE NEXT LINE AND APPLY THAT VOLTAGE TO THE A-REF PIN

                                    //   analogReference(EXTERNAL);   

  lcd.clear();

  lcd.setCursor(0,0);

  lcd.print("Engineers Garage");


  ser.begin(9600);


  ser.println("AT");

  delay(1000);

  ser.println("AT+GMR");

  delay(1000);

  ser.println("AT+CWMODE=3");

  delay(1000);

  ser.println("AT+RST");

  delay(5000);

  ser.println("AT+CIPMUX=1");

  delay(1000);

  String cmd="AT+CWJAP="EngineersGarage","egP@$$w0rd?"";

  ser.println(cmd);

  delay(1000);

  ser.println("AT+CIFSR");

  delay(1000);

}


//  Where the Magic Happens

void loop()

{

   serialOutput();  



  if (QS == true) // A Heartbeat Was Found

    {     

      // BPM and IBI have been Determined

      // Quantified Self "QS" true when arduino finds a heartbeat

      fadeRate = 255; // Makes the LED Fade Effect Happen, Set 'fadeRate' Variable to 255 to fade LED
 with pulse

      serialOutputWhenBeatHappens(); // A Beat Happened, Output that to serial.     

      QS = false; // reset the Quantified Self flag for next time    

    }



  ledFadeToBeat(); // Makes the LED Fade Effect Happen 

  delay(20); //  take a break


  read_temp();



  esp_8266();

}


void ledFadeToBeat()

{

   fadeRate -= 15;                         //  set LED fade value

   fadeRate = constrain(fadeRate,0,255);   //  keep LED fade value from going into negative numbers!

   analogWrite(fadePin,fadeRate);          //  fade LED

}


void interruptSetup()

{     

  // Initializes Timer2 to throw an interrupt every 2mS.

  TCCR2A = 0x02;     // DISABLE PWM ON DIGITAL PINS 3 AND 11, AND GO INTO CTC MODE

  TCCR2B = 0x06;     // DON'T FORCE COMPARE, 256 PRESCALER 

  OCR2A  = 0X7C;      // SET THE TOP OF THE COUNT TO 124 FOR 500Hz SAMPLE RATE

  TIMSK2 = 0x02;     // ENABLE INTERRUPT ON MATCH BETWEEN TIMER2 AND OCR2A

  sei();             // MAKE SURE GLOBAL INTERRUPTS ARE ENABLED      

} 


void serialOutput()

{   // Decide How To Output Serial. 

 if (serialVisual == true)

  {  

     arduinoSerialMonitorVisual('-', Signal);   // goes to function that makes Serial Monitor Visualizer

  } 

 else

  {

      sendDataToSerial('S', Signal);     // goes to sendDataToSerial function

   }        

}


void serialOutputWhenBeatHappens()

{    

 if (serialVisual == true) //  Code to Make the Serial Monitor Visualizer Work

   {            

     Serial.print("*** Heart-Beat Happened *** ");  //ASCII Art Madness

     Serial.print("BPM: ");

     Serial.println(BPM);

     lcd.clear();

     lcd.print("BPM: ");

     lcd.print(BPM);

   }

 else

   {

     sendDataToSerial('B',BPM);   // send heart rate with a 'B' prefix

     sendDataToSerial('Q',IBI);   // send time between beats with a 'Q' prefix

   }   

}


void arduinoSerialMonitorVisual(char symbol, int data )

{    

  const int sensorMin = 0;      // sensor minimum, discovered through experiment

  const int sensorMax = 1024;    // sensor maximum, discovered through experiment

  int sensorReading = data; // map the sensor range to a range of 12 options:

  int range = map(sensorReading, sensorMin, sensorMax, 0, 11);

  // do something different depending on the 

  // range value:

  switch (range) 

  {

    case 0:     

      Serial.println("");     /////ASCII Art Madness

      break;

    case 1:   

      Serial.println("---");

      break;

    case 2:    

      Serial.println("------");

      break;

    case 3:    

      Serial.println("---------");

      break;

    case 4:   

      Serial.println("------------");

      break;

    case 5:   

      Serial.println("--------------|-");

      break;

    case 6:   

      Serial.println("--------------|---");

      break;

    case 7:   

      Serial.println("--------------|-------");

      break;

    case 8:  

      Serial.println("--------------|----------");

      break;

    case 9:    

      Serial.println("--------------|----------------");

      break;

    case 10:   

      Serial.println("--------------|-------------------");

      break;

    case 11:   

      Serial.println("--------------|-----------------------");

      break;

  } 

}



void sendDataToSerial(char symbol, int data )

{

   Serial.print(symbol);

   Serial.println(data);                

}


ISR(TIMER2_COMPA_vect) //triggered when Timer2 counts to 124

{  

  cli();                                      // disable interrupts while we do this

  Signal = analogRead(pulsePin);              // read the Pulse Sensor 

  sampleCounter += 2;                         // keep track of the time in mS with this variable

  int N = sampleCounter - lastBeatTime;       // monitor the time since the last beat to avoid noise

                                              //  find the peak and trough of the pulse wave

  if(Signal &lt; thresh &amp;&amp; N &gt; (IBI/5)*3) // avoid dichrotic noise by waiting 3/5 of last IBI

    {      

      if (Signal &lt; T) // T is the trough

      {                        

        T = Signal; // keep track of lowest point in pulse wave 

      }

    }


  if(Signal &gt; thresh &amp;&amp; Signal &gt; P)

    {          // thresh condition helps avoid noise

      P = Signal;                             // P is the peak

    }                                        // keep track of highest point in pulse wave


  //  NOW IT'S TIME TO LOOK FOR THE HEART BEAT

  // signal surges up in value every time there is a pulse

  if (N &gt; 250)

  {                                   // avoid high frequency noise

    if ( (Signal &gt; thresh) &amp;&amp; (Pulse == false) &amp;&amp; (N &gt; (IBI/5)*3) )

      {        

        Pulse = true;                               // set the Pulse flag when we think there is a pulse

        digitalWrite(blinkPin,HIGH);                // turn on pin 13 LED

        IBI = sampleCounter - lastBeatTime;         // measure time between beats in mS

        lastBeatTime = sampleCounter;               // keep track of time for next pulse



        if(secondBeat)

        {                        // if this is the second beat, if secondBeat == TRUE

          secondBeat = false;                  // clear secondBeat flag

          for(int i=0; i&lt;=9; i++) // seed the running total to get a realisitic BPM at startup

          {             

            rate[i] = IBI;                      

          }

        }



        if(firstBeat) // if it's the first time we found a beat, if firstBeat == TRUE

        {                         

          firstBeat = false;                   // clear firstBeat flag

          secondBeat = true;                   // set the second beat flag

          sei();                               // enable interrupts again

          return;                              // IBI value is unreliable so discard it

        }   

      // keep a running total of the last 10 IBI values

      word runningTotal = 0;                  // clear the runningTotal variable    


      for(int i=0; i&lt;=8; i++)

        {                // shift data in the rate array

          rate[i] = rate[i+1];                  // and drop the oldest IBI value 

          runningTotal += rate[i];              // add up the 9 oldest IBI values

        }


      rate[9] = IBI;                          // add the latest IBI to the rate array

      runningTotal += rate[9];                // add the latest IBI to runningTotal

      runningTotal /= 10;                     // average the last 10 IBI values 

      BPM = 60000/runningTotal;               // how many beats can fit into a minute? that's BPM!

      QS = true;                              // set Quantified Self flag 

      // QS FLAG IS NOT CLEARED INSIDE THIS ISR

      pulse = BPM;

    }                       

  }


  if (Signal &lt; thresh &amp;&amp; Pulse == true)

    {   // when the values are going down, the beat is over

      digitalWrite(blinkPin,LOW);            // turn off pin 13 LED

      Pulse = false;                         // reset the Pulse flag so we can do it again

      amp = P - T;                           // get amplitude of the pulse wave

      thresh = amp/2 + T;                    // set thresh at 50% of the amplitude

      P = thresh;                            // reset these for next time

      T = thresh;

    }


  if (N &gt; 2500)

    {                           // if 2.5 seconds go by without a beat

      thresh = 512;                          // set thresh default

      P = 512;                               // set P default

      T = 512;                               // set T default

      lastBeatTime = sampleCounter;          // bring the lastBeatTime up to date        

      firstBeat = true;                      // set these to avoid noise

      secondBeat = false;                    // when we get the heartbeat back

    }


  sei();                                   // enable interrupts when youre done!

}// end isr


void esp_8266()

{

   // TCP connection AT+CIPSTART=4,"TCP","184.106.153.149",80 

    String cmd = "AT+CIPSTART=4,"TCP","";

    cmd += "184.106.153.149"; // api.thingspeak.com

    cmd += "",80";

    ser.println(cmd);

    Serial.println(cmd); 

    if(ser.find("Error"))

    {

      Serial.println("AT+CIPSTART error");

      return;

    }

  // prepare GET string GET https://api.thingspeak.com/update?api_key=LHAG4NSIYJ5UWS6U&amp;field1=0rnrn

  String getStr = "GET /update?api_key=";

  getStr += apiKey;

  getStr +="&amp;field1=";

  getStr +=String(temp);

  getStr +="&amp;field2=";

  getStr +=String(pulse);

  getStr += "rnrn";

  // send data length

  cmd = "AT+CIPSEND=4,";

  cmd += String(getStr.length());

  ser.println(cmd);

  Serial.println(cmd);

  delay(1000);

  ser.print(getStr);

  Serial.println(getStr);

 //thingspeak needs 15 sec delay between updates

  delay(3000);

}


void read_temp()

{

  int temp_val =  analogRead(A1);

  float mv = (temp_val/1024.0)*5000; 

  float cel = mv/10;

  temp = (cel*9)/5 + 32;

}
</code></pre>
 37622: <p>The sketch in the question is not for NodeMCU. It is for Arduino with esp8266 wired on pins 9 and 10. But the error in title is a current error for esp8266 Arduino boards package 2.6.0. The EspSoftwareSerial bundled with the esp8266 Arduino boards package version 2.6.0 has a compatibility breaking change.</p>

<p>The problem was immediately <a href="https://github.com/esp8266/Arduino/issues/6737" rel="nofollow noreferrer">reported</a> and the EspSoftwareSerial maintainer added the legacy API back to EspSoftwareSerial. The fixed version will be available with esp8266 boards package 2.6.1, which will be available soon because of multiple problems with 2.6.0. </p>
