Environmental Station - Phase #1 [Project introduction]

Hi everyone, I would like to introduce my project as one of the selected challeger of Summer of Sensors Design Challenge - In the Air Tonight

This sub-challenge is mainly based on the ZMOD4510-EVK Outdoor Air Quality Sensor, provided as an evaluation board with USB interface:

 ZMOD4510-EVK

Lately, a nice Humidity and Temperature Sensor (HS4000) was added to the kit:

HS4000-EVK

Project overview

A weather station is of course one of the most popular electronics projects, probably after the bench power supply…so it’s difficult to propose a really new and interesting project.

At the same time, it’s difficult to do something different to measure the air quality, with an air quality sensor!

But if you want to monitor the environment where you live a simple but affordable weather station is still a little bit expensive. And if you want to monitor the air quality, besides basic data (temperature, humidity, pressure and wind), a commercial sensor could be really expensive.

My goal is to design a nice and smart weather station with air quality monitor, easily replicable by other electronics enthusiasts, with quite low costs but performance comparable to some professional instruments.

My “Environmental Station” will be based on an ESP32 Wi-Fi module, in order to access the data from a webserver.

Air quality measurement

With the ZMOD4510 sensor, we can obtain the following data:

• Air Quality Index (between 0 and 500), derived from non-selective measurement of nitrogen dioxide (NO₂) and ozone (O₃)
• Ozone (O₃) concentration (between 20 and 500 ppb), from selective measurement

Weather sensors

We need at least to measure temperature, humidity and pressure. To do this, in my first design idea, I wanted to use the famous BME280 sensor, also easily available as a module.

The HS4000 temperature and humidity sensor was lately added to this sub-challenge, so I'm thinking about using it for my weather station, of course. But the air pressure is an essential parameter and a single barometric air pressure sensor is harder to find and more expensive than the integrated BME280. Also the resolution and accuracy for temperature and humidity are similar for these 2 sensors, so it's difficult to make a decision about this.  

I will also leave a free accessible serial interface, to connect an anemometer (wind sensor) or other sensors (like rain meter) outside the main unit.

Enclosure - Stevenson screen

A Stevenson screen is needed to protect the sensors and electronics against precipitation and direct heat radiation from outside, while still allowing air to circulate freely around them.

This is part of a standard weather station. We can’t design a weather station in a box without good ventilation or with a black enclosure. Otherwise the data will be no realistic.

Shall we buy a professional weather station screen for one hundred euros? No, of course! Let’s build one from cheap materials…we need only few small plastic plates and put them together with long screws.

Since this solution is not professional and certified, we need to test and validate the efficiency. For this reason the temperature and humidity sensors evaluation kit, with remote modules provided, will be really useful for this scope!

How? Simple...after I build the Stevenson screen, I will put it under the sun, with a remote sensor inside. Then I will put another sensor in a really shadow place, like under a big canopy or under a tree. Comparing the different temperatures at the same time, I will test if the sensor inside my screen is influenced or not by the direct sunlight.

Image source: Wikimedia (link)

Power supply

The power of this station will be provided by a small solar panel, with Li-Ion batteries. A simple battery charger and management will be designed, calculating the required minimum input power from the solar panel and battery capacity, from the overall power consumption and operating/standby ratio.

Block diagram

Preliminary planning

This is the basic roadmap of my project. But of course, it's a DIY project and I will provide the requirements myself, so the plan may change underway, especially following valuable feedback from the community!