Can't sync ESP32 with Blynk

Question

I was trying to display the readings of my dht11 sensor on the Blynk dashboard but I am struggling a lot. A little help would be really appreciated.

#define BLYNK_PRINT Serial

/* Fill in information from Blynk Device Info here */
#define BLYNK_TEMPLATE_ID "TMPL3cu_fjr1u"
#define BLYNK_TEMPLATE_NAME "DHT11 Example"
#define BLYNK_AUTH_TOKEN "bpPlBa8ehOqw0sJLKJeO1thMlulVXUCY"

#include <DHT.h>
#include <WiFi.h>
#include <WiFiClient.h>
#include <BlynkSimpleEsp32.h>

// Your WiFi credentials.
// Set password to "" for open networks.
char ssid[] = "***";
char pass[] = "***";

#define DHTPIN 2          // What digital pin we're connected to

// Uncomment whatever type you're using!
#define DHTTYPE DHT11     // DHT 11

DHT dht(DHTPIN, DHTTYPE);
BlynkTimer timer;

// This function sends Arduino's up time every second to Virtual Pin (5)
void sendSensor()
{
  float h = dht.readHumidity();
  float t = dht.readTemperature(); // or dht.readTemperature(true) for Fahrenheit

  if (isnan(h) || isnan(t)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }
  // You can send any value at any time.
  // Please don't send more that 10 values per second.
  Blynk.virtualWrite(V5, h);
  Blynk.virtualWrite(V6, t);
}

void setup()
{
  // Debug console
  Serial.begin(9600);


  dht.begin();

  // Setup a function to be called every second
  timer.setInterval(1000L, sendSensor);
}

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

When I run this, it gets uploaded with no error, but Blynk shows that the device is offline and this is shown in the serial monitor of Arduino IDE:

15:38:20.658 -> ELF file SHA256: 4b7072eae
15:38:20.699 -> 
15:38:20.735 -> Rebooting...
15:38:20.735 -> �[5001] Connecting to 0.0.0.0
15:38:26.059 -> 
15:38:26.092 -> assert failed: xQueueSemaphoreTake queue.c:1709 (( pxQueue ))
15:38:26.181 -> 
15:38:26.181 -> 
15:38:26.181 -> Backtrace: (some lot of characters)
15:38:26.512 -> 
15:38:26.512 -> 
15:38:26.545 -> 
15:38:26.545 -> 
15:38:26.545 -> ELF file SHA256: 4b7072eae
15:38:26.578 -> 
15:38:26.578 -> Rebooting...
15:38:26.614 -> ��[5001] Connecting to 0.0.0.0
15:38:35.107 -> 
15:38:35.140 -> assert failed: xQueueSemaphoreTake queue.c:1709 (( pxQueue ))
15:38:35.206 -> 
15:38:35.206 -> 
15:38:35.206 -> Backtrace: (some lot of characters)
15:38:35.590 -> 
15:38:35.590 -> 
15:38:35.590 -> 
15:38:35.590 -> 
15:38:35.626 -> ELF file SHA256: 4b7072eae
15:38:35.626 -> 
15:38:35.626 -> Rebooting...
15:38:35.668 -> �

Please help

you don't have the necessary WiFi credentials to connect to your LAN — jsotola
– jsotola, Commented Apr 8 at 19:20

hcheung · Accepted Answer · 2025-04-09 02:11:08Z

1

Call Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass) to establish a WiFi connection first.

See ESP32_WiFi.ino example.

answered Apr 9 at 2:11

hcheung

1,9789 silver badges16 bronze badges

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tepalia · Accepted Answer · 2025-04-24 16:22:43Z

1

You're missing the Blynk.begin(auth, ssid, pass) call. Without it, Blynk never initializes properly, and that causes the queue/semaphore crash. The setup must look like this:

void setup()
{
  Serial.begin(9600);
  delay(1000); // Give time to serial to initialize

  Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass);
  dht.begin();

  timer.setInterval(1000L, sendSensor);
}

answered Apr 24 at 16:22

tepalia

1936 bronze badges

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