My DHT11 keeps giving wrong values—what’s wrong?

 If your DHT11 is giving wrong readings (e.g., unrealistic humidity/temperature values, NaN errors, or erratic data), here are the most common causes and fixes:

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1. Wiring Issues (Most Common Problem)

Check:

• Pull-up resistor: A 4.7kΩ–10kΩ resistor must connect the DATA line to VCC (DHT11 won't work reliably without it).

• Loose connections: Ensure wires are firmly plugged into the correct pins.

• Short circuits: Check if any wires are touching accidentally.

Fix:

• Re-wire the circuit like this:

  text

  DHT11 VCC → 5V  
  DHT11 GND → GND  
  DHT11 DATA → Digital Pin (e.g., D2)  
  4.7kΩ resistor between DATA and VCC  

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2. Power Supply Problems

Symptoms:

• Readings are 0, -999, or randomly jump.

• Sensor gets warm (indicates a wiring mistake).

Fix:

• Use a stable 5V supply (some 3.3V boards may not provide enough power).

• If using a long cable (>1m), add a 100nF capacitor between VCC and GND near the sensor to reduce noise.

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3. Software Errors

Symptoms:

• NaN (Not a Number) or failed readings.

• Values don’t change or freeze.

Fix:

• Increase the delay between readings (DHT11 needs ≥1 second between polls).

  cpp

  void loop() {
    delay(2000);  // Wait 2 seconds (DHT11 max rate = 1Hz)
    float h = dht.readHumidity();
    // ...
  }

• Update the library: Use the latest "DHT sensor library" by Adafruit.

• Add error handling:

  cpp

  if (isnan(h) || isnan(t)) {
    Serial.println("Sensor error!");
    delay(1000);
    return;  // Skip this loop
  }

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4. Sensor Placement & Environment

Problems:

• Condensation: High humidity can cause water to form inside the sensor, corrupting data.

• Heat sources: Placing the sensor near heaters, sunlight, or MCUs can skew readings.

Fix:

• Keep the sensor in a ventilated, dry area.

• Avoid direct contact with water (use a protective cover if needed).

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5. Faulty Sensor (Last Resort)

Test:

• Try a different DHT11 (they’re cheap and sometimes defective).

• Test with a DHT22 (more reliable) if precision matters.

Signs of a Dead Sensor:

• Always returns NaN or the same value.

• Gets excessively hot when powered.

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Quick Checklist

Issue	Solution
No data/wrong values	Check pull-up resistor & wiring
NaN errors	Increase delay, update library
Erratic jumps	Add capacitor, stabilize power
Sensor warm	Disconnect immediately (wrong wiring)