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6.2 Measuring Temperature and Humidity with DHT11

In this lesson, we’ll learn how to use a DHT11 temperature and humidity sensor with the Raspberry Pi Pico 2. The DHT11 is a basic, low-cost digital sensor that can measure ambient temperature and humidity, providing a calibrated digital output.

What You’ll Need

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Newton Lab Kit	450+	Newton Lab Kit

You can also buy them separately from the links below.

SN	COMPONENT	QUANTITY	LINK
1	Raspberry Pi Pico 2	1	BUY
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	DHT11 Humiture Sensor	1	BUY

Understanding the DHT11 Sensor

The DHT11 sensor uses a capacitive humidity sensor and a thermistor to measure the surrounding air. It outputs a digital signal on the data pin, and it’s fairly simple to use, but requires precise timing to read data.

Temperature Range: 0–50 °C with ±2 °C accuracy
Humidity Range: 20–80% RH with ±5% accuracy
Sampling Rate: 1 Hz (once every second)

Circuit Diagram

sch_dht11

Wiring Diagram

wiring_dht11

Writing the Code

Let’s write a MicroPython program to read temperature and humidity values from the DHT11 sensor.

Note

Open the 6.2_temperature_humidity.py from newton-lab-kit/micropython or copy the code into Thonny, then click “Run” or press F5.
Ensure the correct interpreter is selected: MicroPython (Raspberry Pi Pico).COMxx.
Here you need to use the library called dht.py, please check if it has been uploaded to Pico, for a detailed tutorial refer to Upload the Libraries to Pico.

from machine import Pin
import utime
import dht

# Initialize the DHT11 sensor
sensor = dht.DHT11(Pin(16))

while True:
   try:
      # Trigger measurement
      sensor.measure()
      # Read values
      temperature = sensor.temperature  # In Celsius
      humidity = sensor.humidity        # In Percent
      # Print values
      print("Temperature: {}°C   Humidity: {}%".format(temperature, humidity))
   except OSError as e:
      print("Failed to read sensor.")
   # Wait before the next reading
   utime.sleep(2)

Once the code is running, the temperature and humidity readings will display in the Thonny Shell.

Temperature: 29.3°C   Humidity: 60.0%
Temperature: 29.2°C   Humidity: 60.0%
Temperature: 29.2°C   Humidity: 60.0%
Temperature: 29.1°C   Humidity: 60.0%
Temperature: 29.2°C   Humidity: 60.0%
Temperature: 29.3°C   Humidity: 60.0%

Understanding the Code

Import Modules:
- machine.Pin: For controlling the GPIO pins.
- utime: Contains time-related functions.
- dht: The library for DHT sensors.

Initialize the Sensor:

sensor = dht.DHT11(Pin(16))
Creates an instance of the DHT11 sensor connected to GP16.

Main Loop:

sensor.measure(): Triggers the sensor to take a measurement.
sensor.temperature: Reads the temperature in Celsius.
sensor.humidity: Reads the humidity percentage.
Exception Handling: Catches any errors that occur during reading.
utime.sleep(2): Waits 2 seconds between readings.

while True:
   try:
      sensor.measure()
      temperature = sensor.temperature
      humidity = sensor.humidity
      print("Temperature: {}°C   Humidity: {}%".format(temperature, humidity))
   except OSError as e:
      print("Failed to read sensor.")
   utime.sleep(2)

Experimenting Further

Convert Temperature to Fahrenheit:

temperature_f = temperature * 9 / 5 + 32
print("Temperature: {}°F   Humidity: {}%".format(temperature_f, humidity))

Display Readings on an LCD:

Integrate an LCD display to show the readings without a computer.
Set Up Alerts:

Use an LED or buzzer to alert when temperature or humidity exceeds certain thresholds.

Troubleshooting Tips

Incorrect Readings:
- Ensure the sensor is connected properly.
- Check for loose wires or poor connections.
Failed to Read Sensor:

This may happen occasionally due to timing issues. The code includes a try-except block to handle this.
Pull-Up Resistor:

If the sensor doesn’t work, ensure that a pull-up resistor is connected between VCC and Data pins if your sensor requires it.

Conclusion

In this lesson, you’ve learned how to use the DHT11 temperature and humidity sensor with the Raspberry Pi Pico 2. Monitoring environmental conditions is a fundamental aspect of many projects, from weather stations to home automation systems.

Try Statement - Python Docs