[SOLVED] Not able to send a string to hardware serial with Blynk


I am trying to send a command Serial3.print(“T,44/r”); to the PH circuit (Atlas scientific EZO), but nothing gets sent. After 2 days of debugging I found out it’s because I added Blynk to my project. So it looks like one of the Blynk libraries/functions is conflicting with the hardware serial print. Anyone had this issue before? and is there a way to fix it?

@haidar have you tried the Blynk basics for your particular internet connected hardware?

Are you going to show us the sketch that you can’t make work:

Hi Costas,

Here is my sketch. Sorry, I didn’t clean it up yet. Hope it’s readable. Everything is working fine except the Serial3.print(“T,44/r”); it doesn’t get sent to the pH circuit. While when i put it in a simple sketch, it does work.

#include <ESP8266_Lib.h> //for Blynk
#include <BlynkSimpleShieldEsp8266.h>//for Blynk
#include <SimpleTimer.h>//for Blynk
#include <OneWire.h> //for temp sensor
#include <DallasTemperature.h> //for temp sensor
SimpleTimer timer; //simple timer for Blynk
#define ONE_WIRE_BUS 8 //pin 8 is for temp sensor
#define BLYNK_PRINT Serial
OneWire oneWire(ONE_WIRE_BUS); //for temp sensor
DallasTemperature sensors(&oneWire); //for temp sensor

//STARTwater flow sensor-------------------------------------------

// which pin to use for reading the sensor? can use any pin!
#define TONE_PIN 6 // buzzer output is pin 6

// count how many pulses!
volatile uint16_t pulses = 0;
// track the state of the pulse pin
volatile uint8_t lastflowpinstate;
// you can try to keep time of how long it is between pulses
volatile uint32_t lastflowratetimer = 0;
// and use that to calculate a flow rate
volatile float flowrate;
// Interrupt is called once a millisecond, looks for any pulses from the sensor!
  uint8_t x = digitalRead(FLOWSENSORPIN);

  if (x == lastflowpinstate) {
    return; // nothing changed!

  if (x == HIGH) {
    //low to high transition!
  lastflowpinstate = x;
  flowrate = 1000.0;
  flowrate /= lastflowratetimer;  // in hertz
  lastflowratetimer = 0;

void useInterrupt(boolean v) {
  if (v) {
    // Timer0 is already used for millis() - we'll just interrupt somewhere
    // in the middle and call the "Compare A" function above
    OCR0A = 0xAF;
    TIMSK0 |= _BV(OCIE0A);
  } else {
    // do not call the interrupt function COMPA anymore
    TIMSK0 &= ~_BV(OCIE0A);

//END water flow sensor--------------------------------------------------------------

float tempC;
int sumpfloatswitch = 0; //for wc
int selectedwateramount = 0; //for wc
int wcinp = 0; //for testing water change action
int waterChangeAmount = 0;
float liters = 0;
String enteredstring;
String wcamount;
String wccommandString;

char auth[] = "MyBlynkAuthCode";//Blynk auth code
#define EspSerial Serial1//for Blynk
// Your ESP8266 baud rate:
#define ESP8266_BAUD 9600
ESP8266 wifi(&EspSerial);//for Blynk

WidgetLCD lcd(V1); //define Blynk LCD
WidgetTerminal terminal(V5);
char ph_data[20];
byte ph_string_received = 0;
byte ph_received_from_sensor = 0;
String inputstring = "";                              //a string to hold incoming data from the PC
String sensorstring = "";                             //a string to hold the data from the Atlas Scientific product
boolean input_string_complete = false;                //have we received all the data from the PC
boolean sensor_string_complete = false;               //have we received all the data from the Atlas Scientific product
float pH;                                             //used to hold a floating point number that is the pH

//++++++++++++++++++++++++++++++++++++++++++++++++++START SETUP++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

void setup()
  // Set ESP8266 baud rate
  Serial3.begin(9600); //PH serial
  inputstring.reserve(10);                          //PH - set aside some bytes for receiving data from the PC
  sensorstring.reserve(30);                         //PH - set aside some bytes for receiving data from Atlas Scientific product
  Blynk.begin(auth, wifi, "MYSSID", "MYPW");// for Blynk
  sensors.begin();//Start Temperature sensor

  pinMode(3, INPUT); //sump high float switch
  pinMode(9, OUTPUT); //res pump
  pinMode(10, OUTPUT); // sump pump
  digitalWrite(9, LOW);
  digitalWrite(10, LOW);

  digitalWrite(FLOWSENSORPIN, HIGH);
  lastflowpinstate = digitalRead(FLOWSENSORPIN);

  timer.setInterval(2000L, sendTempToGraphBlynk);
  timer.setInterval(2500L, sendPHToGraphBlynk);

//++++++++++++++++++++++++++++++++++++++++++++++++++END SETUP++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

void serialEvent3() {                                 //if the hardware serial port_3 receives a PH reading
  sensorstring = Serial3.readStringUntil(13);         //read the string until we see a <CR>
  sensor_string_complete = true;                      //set the flag used to tell if we have received a completed string from the PH sensor

//++++++++++++++++++++++++++++++++++++++++++++++++++START VOID LOOP++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

void loop() {

  Blynk.run(); // run Blynk process
  timer.run(); // Initiates SimpleTimer

  if (input_string_complete == true) {
    inputstring = ""; input_string_complete = false;


//++++++++++++++++++++++++++++++++++++++++++++++++++END VOID LOOP++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


//-------------START send temp Blynk------------//
void sendTempToGraphBlynk()
  char buffer[10]; //buffer for the temperature
  String temperature = dtostrf(tempC, 4, 2, buffer); //convert the temperature to a string

  Blynk.virtualWrite(2, tempC);

//-------------END send temp Blynk graph------------//

//-------------START send pH on Blynk graph------------//
void sendPHToGraphBlynk()

  char pH_buffer[10]; //buffer for the ph

  String pHstring = dtostrf(pH, 3, 2, pH_buffer); //convert the pH to a string
  Blynk.virtualWrite(3, 8.2);


//-------------END send pH on Blynk  graph------------//

//-------------Start Get Temperature Function------------//
void GetTemperature()

  sensors.requestTemperatures(); // Send the command to get temperatures
  tempC =  sensors.getTempCByIndex(0);
//-------------End Get Temperature Function------------//

//----------START---------Receive command from Blynk terminal and excute accordingly----------------------------------
  enteredstring = param.asStr();
  wcamount = enteredstring.substring(13);
  wccommandString = enteredstring.substring(0, 12);
  waterChangeAmount = wcamount.toInt();

  if (String("water change") == wccommandString) {

    wcinp = 1;


  else if (String("hi") == param.asStr())
    terminal.print("Hi Haidar enter a command please");


  else if (String("hi") == param.asStr())
    terminal.print("Hi, enter a command please");

  else if (String("help") == param.asStr())
    terminal.println("You can enter the following commands:");
    terminal.println("- water change #");


  else if (String("ph temp") == param.asStr())


    while (sensor_string_complete == true) {               //if a string from the Atlas Scientific product has been received in its entirety
      //Serial.println(sensorstring);                     //send that string to the PC's serial monitor

      sensorstring = "";                                  //clear the string:
      sensor_string_complete = false;



  else {
    // Send it back
    terminal.write(param.getBuffer(), param.getLength());
    terminal.print(" is unknown command");
  // Ensure everything is sent


//----------END---------Receive command from Blynk terminal and excute accordingly----------------------------------

//-----------------Start get PH function-----------------//

void GetPH() {
  if (sensor_string_complete == true) {               //if a string from the Atlas Scientific product has been received in its entirety
    //Serial.println(sensorstring);                     //send that string to the PC's serial monitor
    if (isdigit(sensorstring[0])) {                   //if the first character in the string is a digit
      pH = sensorstring.toFloat();                    //convert the string to a floating point number so it can be evaluated by the Arduino
  sensorstring = "";                                  //clear the string:
  sensor_string_complete = false;    //reset the flag used to tell if we have received a completed string from the Atlas Scientific product

//-----------------End get PH function-----------------//

//------START Water change function---------------------
void changeWater (int selectedwateramount)



  pulses = 0; //added code witout testing
  liters = 0; //added code witout testing

  if (selectedwateramount > 0) {
    terminal.print("System will change ") ;

    terminal.println(" liters") ;

    tone(2, 3000, 3000);

    terminal.println("Water started...") ;
    while (liters < selectedwateramount) {
      Blynk.run(); // run Blynk process
      liters = pulses; //flow sensor
      liters /= 7.5; //flow sensor
      liters /= 60.0; //flow sensor
      //Serial.print(liters); Serial.println(" Liters");
      terminal.println("Draining water");

      terminal.print(" ltr ");
      //lcd.setCursor(9, 1);
      terminal.print(liters / selectedwateramount * 100);

      //switch on sump pump
      digitalWrite(9, LOW);
      digitalWrite(10, HIGH);
    sumpfloatswitch = digitalRead(3); //added code witout testing
    while (liters >= selectedwateramount && sumpfloatswitch == LOW) {
      Blynk.run(); // run Blynk process
      sumpfloatswitch = digitalRead(3);
      terminal.println("* Adding water *");
      //switch on res pump
      digitalWrite(9, HIGH);
      digitalWrite(10, LOW);
      //blinking adding water text
    if (sumpfloatswitch == HIGH) {
      //delay(2000); to eliminate sensor sensitivity should be added later somehow
      Blynk.run(); // run Blynk process
      terminal.println("Water change completed");
      tone(2, 1000, 10000);
      pulses = 0;
      liters = 0;
      selectedwateramount = 0;
      digitalWrite(9, LOW);
      digitalWrite(10, LOW);


  else {
    terminal.println("Please enter a valid amount");

//------END Water change function---------------------

The library does not try to refer to Serial objects, except those you point to… like BLYNK_PRINT.
Maybe, your shields use the same pins, or some other reason.
Also, you can check the source and try figuring out the reason.

Thanks vhymanskyy. My pH circuit is connected to TX/RX3 while my wifi module (ESP8266) is connected to TX/RX1. So i don’t this there is an issue with the pins. I also changed the pH circuit to serial 2, but this didn’t fix the issue.

are you sure it’s not the Serial3.print("T,44\r"); ? I mean the \r part…

I am sure it’s “/r”. as the same Serial3.print(“T,44/r”); works fine when I remove the Blynk widgets from the sketch.

I resolved the issue by using \r instead of /r which was a typo by the the Atlas technical service team. I have tried that many times but it didn’t work. After 2 days of debugging, I found out I had to add a delay of 100 ms before the Blynk run. I know its not recommended to use delays, but this was the only way to get it to work.
I am now using the terminal to send commands, so a big thank to the Blynk team for the great work that has been put in development as well as support.

1 Like

Hi Haidar,
I have the same problem with same Circuit of pH and i have try to put delay of 100 ms but it id=s still unfix.

@yaamr FYI you are responding to a year old post :wink:

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