MicroPython Driver for DHT12 Sensor

Contents

• Introduction
• Connecting the DHT12
• Driver Overview
• Reading Temperature and Humidity
• Driver Code
• Example

Introduction

This a MicroPython driver written specifically for the BBC micro:bit that will work with the DHT12 relative humidity and ambient temperature sensor.

This sensor's only user options are to read relative humidity and temperature. The sensor also returns a validation checksum with this data. This driver provides methods to do exactly this for the user's MicroPython program.

The DHT12 sensor is discussed in some detail here.

The DHT12 is probably now out of production but can still be found (early 2025). The sensor is encased in a tough (probably) ABS plastic casing with four pins exposed. The pins have 2.54mm spacing making this device breadboard friendly.

Connecting the DHT12

The DHT12 communicates via I²C. It also has a 1-wire interface that is backwardly compatible with the older DHT11. This driver does't cater for the 1-wire interface. It's written to exclusively communicate with the sensor via I²C.

Care must be taken when inserting the DHT12 module into a breadboard. The pins are quite thin and bend quite easily. Place the pins over the holes in the breadboard and just wriggle the sensor gently to insert.

Use Fig 1 above as a guide to locating the correct pins on the sensor. The micro:bit and the DHT12 must be connected as follows:

This utilises the standard I²C pins of the micro:bit. No external pullup resistors are required as the micro:bit's I²C pins have internal pullups that nicely do the job of keeping SCL and SDA in a HIGH state when the bus is idle.

Driver Overview

The driver code can be:

• Copied from this webpage onto the clipboard then pasted into the MicroPython editor e.g. the Mu Editor. It should be saved as fc_dht12.py  - OR -
• Download as a zip file using the link. Unzip the file and save it as fc_dht12.py into the default directory where the MicroPython editor e.g. Mu Editor saves python code files.

After saving the fc_dht12.py file to the computer it should be copied to the small filesystem on the micro:bit. The examples on this page will not work if this step is omitted. Any MicroPython editor that recognises the micro:bit will have an option to do this.

The Mu Editor is recommended for its simplicity. It provides a Files button on the toolbar for just this purpose.

The driver is implemented as a class. The first thing to do is call the constructor. This provides an instance of the class.

Syntax:
instance = DHT12()

Example
from fc_dht12 import *
my_sensor = DHT12()
          

The constructor has no arguments. The I²C address for the DHT12 is 0x5C. This is fixed and cannot be changed.

This assumes that the file fc_dht12.py has been successfully copied to the micro:bit's filesystem as described above.

The driver provides three methods and one function that:

• Read(), T(), RH() : Methods to read the relative humidity and ambient temperature.
• CtoF() : Function to convert °C to °F.

Reading Temperature and Humidity

There are three methods that return the humidity and/or temperature.

Read()
Returns a tuple containing three values:
  [0] is relative humidity in %RH,
  [1] is temperature in °C
  [2] is the result of comparing the sensor
      checksum with the calculated checksum.
      A value of True indicates a high
      data confidence.

Relative humidity and temperature are
returned with a precision of one decimal.

RH()
Returns relative humidity in %RH
The result is returned as an integer.

T()
Returns temperature in °C

Example:
# Test the DHT12 MicroPython
# driver for the micro:bit.

from fc_dht12 import *
from microbit import sleep

dht12 = DHT12()
x = 1

# Test every method of the driver 5 times.
while (x < 6):
    # Do full sensor read.
    print(dht12.Read())
    
    # Get only humidity
    rh = dht12.RH()
    
    # Get only temperature
    # Convert to fahrenheit
    Ctemp = dht12.T()
    Ftemp = CtoF(Ctemp)
    
    # Report humidity
    # Report temperature (C and F).
    print('RH =', rh,
          ', C =', Ctemp,
          ', F =', Ftemp, '\n')
    
    # Wait 10 minutes before next readings.
    x += 1
    if (x != 6):
      sleep(600000)

Sample Output:
[13.3, 25.2, True]
RH = 13 , C = 25.2 , F = 77.4 

[13.4, 25.2, True]
RH = 15 , C = 25.6 , F = 78.1 

[13.4, 25.5, True]
RH = 16 , C = 25.8 , F = 78.4 

[15.9, 25.7, True]
RH = 15 , C = 26.1 , F = 79.0 

[14.6, 26.2, True]
RH = 15 , C = 26.0 , F = 78.8
          

Note:

The datasheet advises that no more than one reading should be made per two seconds. Attempting to push the DHT12 much harder will often cause MicroPython to throw an OSError exception because there is no response from the sensor on the I²C bus.

The driver incorporates exception catching code to prevent this from occurring.

Enjoy!