SolutionsToTheDHT11TemperatureAndHumiditySensor < IoT_Course

Tags: view all tags

---+ Solutions to exercise 4: The DHT11 Temperature and Humidity Sensor
---++ Exercise 1:

The solution to the exercise is quasi already given in the [[https://docs.micropython.org/en/latest/esp32/quickref.html#dht-driver][MicroPython manual]]. All you need to do is replacing the Pin (4 in the manual) by the pin used with our hardware: pin 16. Here is the solution:

%ATTACHURL%/dht11.py.txt

It takes a new measurement every 2 s and prints the result.
---++ Exercise 2:

When doing the manual evaluation you get:
| | | | | | | | | | | | Combined | Decimal Value | |
| Humidity High | 0 | 0 | 1 | 1 | | 1 | 1 | 1 | 1 | | 0x3f | 63 | Humidity = 63% |
| Humidity Low | 0 | 0 | 0 | 0 | | 0 | 0 | 0 | 0 | | 0x00 | | |
| Temperature | 0 | 0 | 0 | 1 | | 0 | 1 | 1 | 1 | | 0x17 | 23 | Temperature = 23.4°C |
| Temperature Decimal | 0 | 0 | 0 | 0 | | 0 | 1 | 0 | 0 | | 0x04 | 4 | |
| Checksum | 0 | 1 | 0 | 1 | | 1 | 0 | 1 | 0 | | 0x5a | | |
<br />Adding the first 4 hex numbers should result in the same value as the checksum:

<img alt="dht11Checksum.png" src="%ATTACHURL%/dht11Checksum.png" title="dht11Checksum.png" />

The program for automatic data extraction is here:

%ATTACHURL%/dht11Eval.py.txt

and here a screen dump when running it on the data taken:

<img alt="dht11Eval.png" height="60" src="%ATTACHURL%/dht11Eval.png" title="dht11Eval.png" width="914" />
---++ Exercise 3:

The exercise sheet pretty much explains how to proceed. Therefore I just supply the solution for your study. There are 2 different ways on how to convert the binary values in the 32*32 bit array to strings such that you can write them to the file. In the solution I use the newer method while the old style is given in the comments.

Here is the solution that starts a measurement, reads out the raw data and write them to a file named "/data/dht11.txt". If the "/data" directory does not yet exist on the ESP32 it is created.

%ATTACHURL%/dht11RawRead.py.txt
---++ Exercise 4:

In the script

%ATTACHURL%/dht11Unpack.py.txt

the file dth11.txt is opened and unpacked. The sequence if bits is written to the file "dht11Unpacked.txt". This file can be easily plotted with gnuplot:

<i>gnuplot</i><br /><i>plot [0:900][0:1.5] "dht11Unpacked.txt" with lines</i>

The script

%ATTACHURL%/dht11Plot.py.txt

does unpacking and plotting in a single script. It uses matplotlib to produce the plot.

-- %USERSIG{UliRaich - 2020-05-14}%

---++ Comments

%COMMENT%

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who
txt	dht11.py.txt	r1	manage	0.7 K	2020-05-14 - 12:56	UliRaich
png	dht11Checksum.png	r1	manage	4.6 K	2020-05-30 - 14:31	UliRaich
png	dht11Eval.png	r1	manage	19.6 K	2020-05-30 - 14:28	UliRaich
txt	dht11Eval.py.txt	r3 r2 r1	manage	2.0 K	2020-05-30 - 14:28	UliRaich
txt	dht11Plot.py.txt	r2 r1	manage	1.1 K	2020-05-14 - 13:51	UliRaich
txt	dht11RawRead.py.txt	r1	manage	0.8 K	2020-05-14 - 13:42	UliRaich
png	dht11Result.png	r1	manage	18.5 K	2020-05-14 - 13:26	UliRaich
txt	dht11Unpack.py.txt	r2 r1	manage	1.1 K	2020-05-14 - 13:53	UliRaich

Topic revision: r2 - 2020-05-30 - UliRaich