Issue with serial COM port Arduino Uno using blynk with usb

Solved
1

Hello,

my project is to monitor home energy using Arduino. I have done the simple blink blynk where I controlled Arduino led to turn off and on using blynk switch with no problem. However, when I added my sketch to display KWH on blynk app I receive this:
"avrdude: ser_open(): can’t open device “\.\COM5”: Access is denied.

Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
"

here is my code

#include <EmonLib.h>
#include <Blynk.h>
#define BLYNK_PRINT DebugSerial


// You could use a spare Hardware Serial on boards that have it (like Mega)


#include <BlynkSimpleStream.h>
 
EnergyMonitor emon1;
 

#define currCalibration 0.52
 
BlynkTimer timer;

float kWh = 0;
unsigned long lastmillis = millis();
 
// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
char auth[] = "********";


void myTimerEvent() {
  
    emon1.calcVI(20, 2000);
    Serial.print("Vrms: ");
    Serial.print(emon1.Vrms, 2);
    Serial.print("V");
    Blynk.virtualWrite(V0, emon1.Vrms);
    Serial.print("\tIrms: ");
    Serial.print(emon1.Irms, 4);
    Serial.print("A");
    Blynk.virtualWrite(V1, emon1.Irms);
    Serial.print("\tPower: ");
    Serial.print(emon1.apparentPower, 4);
    Serial.print("W");
    Blynk.virtualWrite(V2, emon1.apparentPower);
    Serial.print("\tkWh: ");
    kWh = kWh + emon1.apparentPower*(millis()-lastmillis)/3600000000.0;
    Serial.print(kWh, 4);
    Serial.println("kWh");
    lastmillis = millis();
    Blynk.virtualWrite(V3, kWh);
}
 

void setup()
{
  // Debug console
 Serial.begin(9600);
 emon1.current(A0, currCalibration); // Current: input pin, calibration.
  // Blynk will work through Serial
  // Do not read or write this serial manually in your sketch
  Blynk.begin(Serial, auth);
   timer.setInterval(5000L, myTimerEvent);
}

void loop()
{
  Blynk.run();
  timer.run();
}

Also, no errors when I verify the sketch and I made sure that the correct port is selected from the blynk-sar found in script file.
When I try to open serial monitor, I get the following:
Error opening serial port ‘COM5’. (Port busy)
My guess is there are more than one sketch fighting for the same port but I do not how.

cmd.exe window (always open):
Connecting device at COM5 to blynk-cloudcom:80…
OpenC0C("\.\COM5", baud=9600, data=8, parity=no, stop=1) - OK
Connect(“blynk-cloudcom”, “80”) - OK
InOut() START
DSR is OFF

2

You can’t do Serial.prints when using the serial port as your Blynk connection method.

BlynkSimpleStream requires EXCLUSIVE access to the serial port.

Pete.

3

thank you Pete. ok then is it possible to send sensor data from arduino to Blynk with serial port as my Blynk connection. Ignoring serial.print this time.

4

Yes, of course. Take a look at the other sketch builder examples

Pete.

5

Hi again. I edited the sketch but I still get the following :
avrdude: ser_open(): can’t open device “\.\COM5”: Access is denied.

Problem uploading to board. See for suggestions.

here is my edited code for a reference :

#include <EmonLib.h>
#define BLYNK_PRINT SwSerial
#include <SoftwareSerial.h>

SoftwareSerial SwSerial(11, 12); // RX, TX
#include <BlynkSimpleStream.h>

// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
#define currCalibration 62
#define Volt 120;
EnergyMonitor emon1;
     
float kWh = 0;
unsigned long lastmillis = millis();
char auth[] = "******";

BlynkTimer timer;
// This function sends Arduino's up time every second to Virtual Pin (5).
// In the app, Widget's reading frequency should be set to PUSH. This means
// that you define how often to send data to Blynk App.
void myTimerEvent()
{
  float  amps = emon1.calcIrms(7400);
  float  watt = amps * Volt; 
  kWh = kWh + watt*(millis()-lastmillis)/3600000000.0;
  // You can send any value at any time.
  // Please don't send more that 10 values per second.
  Blynk.virtualWrite(V5, amps);
  Blynk.virtualWrite(V6, kWh); 
  lastmillis = millis(); 
}

void setup()
{
  // Debug console
  SwSerial.begin(9600);
  // Blynk will work through Serial
  // Do not read or write this serial manually in your sketch
  Serial.begin(9600);
  Blynk.begin(Serial, auth);
  emon1.current(A0, currCalibration); // Current: input pin, calibration.
  // Setup a function to be called every second
  timer.setInterval(1000L, myTimerEvent);
}

void loop()
{
  Blynk.run();
  timer.run(); // Initiates BlynkTimer
}

at this point I think maybe because I was running another sketch on COM5(the only thing plugged to my computer) before I tried to connect to Blynk. I restarted Arduino IDE, and my computer but still same issue.

6

I’d start by rebooting your PC with nothing plugged into your USB ports or serial ports other than keyboard, mouse etc.
it’s a PC then you need to go to Device Manager and see what COM ports are available, with and without your Arduino plugged-in.

TBH, using this connection method is really only useful as a way of quickly getting up and running with Blynk before you buy some IoT capable hardware such as a NodeMCU or ESP32.

Maybe time to stop wasting time and effort with this and buy some proper hardware.

Pete.

7

I’d need to order that. I’m behind schedule, and I really need to view the data on Blynk . I got to upload the sketch to Arduino (upload sketch before opening blynk-ser file) but I ran into another issue where the project on Blynk is offline.

8

I finally got it online. I changed SwSerial to DebugSerial. Then, uploaded the sketch, Finally, opened the Blynk-ser file.

9

Hi, I have the same problem as you. Is it possible to share your final code again? I tried to change the SwSerial-positions to DebugSerial, but couldn’t solve the problem so far.
Thank you!