Introduction to Python and Microcontrollers

Hygrothermograph (DHT11)

Read temperature and humidity from a DHT11 sensor and print both to the Shell.

New Concepts

• DHT11

DHT11

The DHT11 is a combined temperature and humidity sensor whose output is already calibrated by the manufacturer — no formulas or lookup tables needed, unlike the Thermistor. It uses a custom single-wire protocol to send data, so reading it relies on the dht driver module rather than a plain GPIO read.

Pin	Description
VCC	Power, 3.3V–5.5V
SDA	Data pin — single-wire communication
NC	Not connected — has no function and should be left unwired
GND	Ground

The sensor takes about 1 second to initialize after power-up.

Component List

Circuit

Disconnect all power before building the circuit. Reconnect once verified.

Wiring Diagram

Connections:

• DHT11 VCC → 3.3V (through a 10kΩ pull-up to the SDA line)
• DHT11 SDA → GPIO21
• DHT11 NC → not connected
• DHT11 GND → GND

Schematic Diagram

Code

File: 03_sensors/code/Hygrothermograph.py

import machine
import time
import dht

DHT = dht.DHT11(machine.Pin(21))

while True:
    try:
        DHT.measure()
        print('temperature:',DHT.temperature(),'humidity:',DHT.humidity())
        time.sleep_ms(2000)
    except:
        pass

How to Run

Online

1. Open Thonny → 03_sensors/code/.
2. Double-click Hygrothermograph.py.
3. Click Run current script — temperature and humidity print to the Shell every 2 seconds.

Code Explanation

Associate the sensor with a pin

DHT = dht.DHT11(machine.Pin(21))

Creates a DHT11 object on GPIO21, the pin wired to the sensor’s SDA line.

Take a reading

DHT.measure()
print('temperature:',DHT.temperature(),'humidity:',DHT.humidity())

measure() triggers a fresh reading over the single-wire protocol; temperature() and humidity() then return the two values from that reading.

Wrap in try/except

while True:
    try:
        DHT.measure()
        ...
    except:
        pass

DHT11 reads occasionally fail (the single-wire timing is sensitive to interference). Wrapping each attempt in try/except means one failed read is silently skipped instead of crashing the loop.

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Key Concepts

• Single-wire protocols: some sensors send all their data over one data pin with precise timing, rather than a standard bus like I2C or UART — these require a dedicated driver module instead of plain GPIO reads
• Calibrated sensors: the DHT11 returns ready-to-use temperature/humidity values directly, unlike the Thermistor, which needs a manual formula to convert resistance into temperature

See Class dht for the full API reference.

Further Exploration

• Average several readings to smooth out occasional bad samples.
• Combine this with Soft Light’s PWM technique to drive a fan or heater indicator based on temperature.

Back to Module

Adapted from Python_Tutorial.pdf Project 24.1

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