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Removed Si7021 and added HYT221 humidity sensor

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marcel
2024-05-02 11:04:41 +02:00
parent 71a3a48af7
commit eeb6bd846c
7 changed files with 103 additions and 149 deletions
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32
build-doc/weather_station.html
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@@ -5,7 +5,7 @@
<meta name="generator" content="pandoc" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes" />
<meta name="author" content="M.T. Konstapel" />
<meta name="dcterms.date" content="2024-01-22" />
<meta name="dcterms.date" content="2024-05-02" />
<title>Weather station</title>
<link rel="stylesheet" href="./css/mvp.css" />
<style type="text/css">
@@ -53,6 +53,9 @@
id="toc-specifications">Specifications</a></li>
<li><a href="#schematic"
id="toc-schematic">Schematic</a></li>
<li><a href="#problems-i-encounter-after-four-months-of-use"
id="toc-problems-i-encounter-after-four-months-of-use">Problems
I encounter after four months of use</a></li>
<li><a href="#software-dependencies"
id="toc-software-dependencies">Software
dependencies</a></li>
@@ -75,7 +78,7 @@
<h1 class="title">Weather station</h1>
<p class="subtitle">with ModBus RTU interface</p>
<p class="author">M.T. Konstapel</p>
<p class="date">2024-01-22</p>
<p class="date">2024-05-02</p>
<p><a href="./weather_station.pdf"><i>PDF version</i></a></p>
</header>
<main>
@@ -868,6 +871,29 @@ Address : 14</code></pre>
<h1 id="schematic">Schematic</h1>
<p><a href="./images/weather_station_schematic.pdf"><img
src="./images/weather_station_schematic.svg" alt="Schematic" /></a></p>
<h1 id="problems-i-encounter-after-four-months-of-use">Problems I
encounter after four months of use</h1>
<p>The Si7021 humidity sensor is not made for outdoor use. The datasheet
is clear about that. But a lot of people use this cheap sensor for
weather stations anyway. So I choose this sensor for my design. But that
was not smart. After an initial time without any problems, the sensor
started to saturate. This happened during a very wet and mild winter we
had. My first solution was to utilize the build in heater to drive of
the moisture. That worked, but only for a short period. The heater blew
up and the sensor started to report humidity levels above 100% and
because of a bug in the firmware of the sensor, the humidity register
wrapped around and the sensor reported humidity levels of 0-30%. I tried
to find a software solution, which worked for a while, but the sensor
deteriorated even more. To the point of being totally useless. So I
searched for another, better sensor. And I found the HYT-221 from
Innovative Sensor Technology. This sensor is designed to work outdoors
and can even be used in saunas, where the humidity levels are always
high and the air is condensating. The datasheet specifically mentions
outdoor weather stations as an application. The only downside is its
price: it is ten times more expensive than the Si7021.</p>
<p>The sensor can be controlled via the I2C bus, so implementing the new
sensor in the firmware was very easy. From version 0.3.0 onward, this
sensor is used. The Si7021 is removed from the code.</p>
<!---
# Bill of materials
@@ -906,7 +932,7 @@ option) any later version.</p>
</main>
<footer>
<p>&copy;
2024-01-22
2024-05-02
M.T. Konstapel
<a href="https://meezenest.nl/mees/">https://meezenest.nl/mees/</a>
</p><p>This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International License</a>.

8
build-doc/weather_station.md
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@@ -2,7 +2,7 @@
title: Weather station
subtitle: with ModBus RTU interface
author: M.T. Konstapel
date: 2024-01-22
date: 2024-05-02
website: https://meezenest.nl/mees/
page_back: https://meezenest.nl/mees/weather_station.html
logo: ./images/mees_logo.svg
@@ -392,6 +392,12 @@ As a housing for the prototype, I used an old beehive. These are weatherproof an
[![Schematic](./images/weather_station_schematic.svg)](./images/weather_station_schematic.pdf)
# Problems I encounter after four months of use
The Si7021 humidity sensor is not made for outdoor use. The datasheet is clear about that. But a lot of people use this cheap sensor for weather stations anyway. So I choose this sensor for my design. But that was not smart. After an initial time without any problems, the sensor started to saturate. This happened during a very wet and mild winter we had. My first solution was to utilize the build in heater to drive of the moisture. That worked, but only for a short period. The heater blew up and the sensor started to report humidity levels above 100% and because of a bug in the firmware of the sensor, the humidity register wrapped around and the sensor reported humidity levels of 0-30%. I tried to find a software solution, which worked for a while, but the sensor deteriorated even more. To the point of being totally useless. So I searched for another, better sensor. And I found the HYT-221 from Innovative Sensor Technology. This sensor is designed to work outdoors and can even be used in saunas, where the humidity levels are always high and the air is condensating. The datasheet specifically mentions outdoor weather stations as an application. The only downside is its price: it is ten times more expensive than the Si7021.
The sensor can be controlled via the I2C bus, so implementing the new sensor in the firmware was very easy. From version 0.3.0 onward, this sensor is used. The Si7021 is removed from the code.
<!---
# Bill of materials