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en:pfw:dht22 [2025-04-25 01:29] – [All about noForth] mkaen:pfw:dht22 [2025-06-26 12:31] (current) – [Aids] mka
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 {{pfw:full-banner.png?500 }} {{pfw:full-banner.png?500 }}
-====== DHT22 Protocol ====== +====== DHT22 ======
-===== Introduction ===== +
 The DHT22 module is a low-cost digital temperature and humidity sensor. It utilizes a capacitive humidity sensor and a thermistor to measure the surrounding air and outputs a digital signal via a single data pin. It's known for its wider measurement range and higher accuracy compared to its predecessor, the DHT11. The DHT22 module is a low-cost digital temperature and humidity sensor. It utilizes a capacitive humidity sensor and a thermistor to measure the surrounding air and outputs a digital signal via a single data pin. It's known for its wider measurement range and higher accuracy compared to its predecessor, the DHT11.
  
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 * Suitable for indoor environmental monitoring, weather stations, and HVAC systems. * Suitable for indoor environmental monitoring, weather stations, and HVAC systems.
  
-===== SDA =====+===== SDA Protocol =====
  
 The DHT22 communicates using a **proprietary single-wire serial protocol**. Here's a breakdown of the process: The DHT22 communicates using a **proprietary single-wire serial protocol**. Here's a breakdown of the process:
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 The microcontroller needs to carefully time these pulses to correctly interpret the data sent by the DHT22. Libraries for popular platforms like Arduino and Raspberry Pi handle these timing-critical operations. The microcontroller needs to carefully time these pulses to correctly interpret the data sent by the DHT22. Libraries for popular platforms like Arduino and Raspberry Pi handle these timing-critical operations.
  
-[[https://wiki.forth-ev.de/lib/exe/fetch.php/pfw:am2302-en-aosong.pdf|am2302-en-aosong.pdf]] This Aosong document has the correct data, although it is a creepy English translation.+[[https://wiki.forth-ev.de/lib/exe/fetch.php/pfw:am2302-en-aosong.pdf|am2302-en-aosong.pdf]] This Aosong document has the correct data, although it is a creepy English translation.  
 + 
 +On page 2, under 4, "The definition of single-bus interface," pin 2 of the sensor is called **SDA, Serial Data**. A table and a figure show the pin assignment of the AM2302.
  
 {{ :en:pfw:dht22-response.png?nolink |Screenshot of the 40-bit response on the SDA line. (PulsView Logic Analyser)}} {{ :en:pfw:dht22-response.png?nolink |Screenshot of the 40-bit response on the SDA line. (PulsView Logic Analyser)}}
  
-===== Implementation ===== + 
-==== Testing with a Logic Analyser (PulsView) ====+===== Testing with a Logic Analyser (PulsView) =====
  
 Pin P1.0 is bidirectional. It sends the start pulse and then receives the 40 data bits from the sensor module. Pin P1.0 is bidirectional. It sends the start pulse and then receives the 40 data bits from the sensor module.
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 {{ :en:pfw:dht22-bit_lesen_mit_2xmoon.png?nolink |The timing is critical. So, it's correct now. Here we read a "0"}} {{ :en:pfw:dht22-bit_lesen_mit_2xmoon.png?nolink |The timing is critical. So, it's correct now. Here we read a "0"}}
  
-==== Pseudocode ====+====== Implementation for TI's Launchpad ======
  
-<code> +This program was used to test DHT22 modules before installation. The DHT22 modules were tested for functionality at room temperature, pre-sorted in this way, and then frozen in a bag of moist sand in the freezer and tested again. One module displayed incorrect temperature values ​​in frost conditions, the display of negative values ​​did not comply with the specifications.
-Function: Pio    ( -- )  \ set port I/O function. SDA --> P1.0  +
-Function: wakeup ( -- )  \ notify sensor to prepare the data +
-Function: @data  ( -- sun moon hum tmp chk chksum )  \ get sensor data +
-  get response time of sensor, store in register 'sun' (just for testing) +
-  get startpulse duration, store in register 'moon' +
-  40 loop  +
-     read bit using 'moon' based delay  +
-     lshift bit into array xx yy zz +
-  08 loop        +
-     lshift array  \ adjust xx yy zz --> hum tmp chk  +
-  calculate chksum +
-Function: (dht22)  ( -- sun moon hum tmp chk chksum ) \ wake up and read sensor +
-Function:  dht22   ( -- )  \ print temperatur and humidity +
-Function:  test    ( n -- ) \ multiple readings   +
-    n loop  dht22 +
-</code> +
- +
-==== Source Code ====+
  
 [[en:pfw:dht22-msp430g2553-noforth|DHT22 with Launchpad MSP430G2553 and noForth]] [[en:pfw:dht22-msp430g2553-noforth|DHT22 with Launchpad MSP430G2553 and noForth]]
  
-==== More information on the MSP430G2553 ==== 
  
 +
 +====== Background Information ======
 +
 +  * How this was discovered: [[en:pfw:dht22tmpformat|The temperature format of the DHT22]]
   * [[https://www.ti.com/lit/ug/slau144j/slau144j.pdf|MSP430x2xx Family guide SLAU144J.PDF]]   * [[https://www.ti.com/lit/ug/slau144j/slau144j.pdf|MSP430x2xx Family guide SLAU144J.PDF]]
   * [[https://www.ti.com/lit/ds/symlink/msp430g2553.pdf|MSP430G2553 datasheet SLAS735J.PDF]], port data on page 49ff   * [[https://www.ti.com/lit/ds/symlink/msp430g2553.pdf|MSP430G2553 datasheet SLAS735J.PDF]], port data on page 49ff
 +  * [[https://home.hccnet.nl/anij/nof/noforth.html| noforth.html - find your version, docmentation,  tool.f and asm.f here.]] All about noForth.
  
-==== All about noForth ==== +====== Aids ======
- +
-[[https://home.hccnet.nl/anij/nof/noforth.html| noforth.html - find your version, docmentation,  tool.f and asm.f here.]] +
- +
---- +
- +
-=== Source code editor ===+
  
 I like //Notepad Next// for Linux, a cross-platform, reimplementation of //Notepad++//. I like //Notepad Next// for Linux, a cross-platform, reimplementation of //Notepad++//.
-https://github.com/dail8859/NotepadNext +https://github.com/dail8859/NotepadNext\\
- +
-=== Terminal === +
 To work with the embedded noForth system I use //e4thcom// by Manfred Mahlow. To work with the embedded noForth system I use //e4thcom// by Manfred Mahlow.
-https://wiki.forth-ev.de/doku.php/projects:e4thcom +https://wiki.forth-ev.de/doku.php/projects:e4thcom\\ 
- +Sometimes I also use Windows and Teraterm, for example, to log longer MCU outputs to a file. I also prefer it for testing parts of the source code using copy and paste.\\
-=== Logic Analyser === +
 AZDelivery Logic Analyzer 8 CH, 24MHz. (Amazon)\\ AZDelivery Logic Analyzer 8 CH, 24MHz. (Amazon)\\
 //PulseView// is a Qt-based logic analyzer and oscilloscope GUI for sigrok. //PulseView// is a Qt-based logic analyzer and oscilloscope GUI for sigrok.
- 
---- 
  
en/pfw/dht22.1745537379.txt.gz · Last modified: 2025-04-25 01:29 by mka