ESP8266 DHT22 Web Server

This project is to program ESP8266 boards to offer a simple HTTP server to read temperature and humidity data of an attached DHT22 sensor.

The Server

The server code, under dht22-web, is developed for ESP8266 chipset. I used Arduino IDE to develop and upload this code on all my ESP8266 chipsets.

API

The service offers a very simple API which is specified in the swagger.yml file:

Reading

GET / provides the current reading of the sensor.

Example response:

{
    "deltaTime": 0,
    "device": "dht22-03",
    "dht22": {
        "heatIndex": 21.85072,
        "humidity": 61.1,
        "temperature": 22
    },
"stale": 0
}

where

• deltaTime specifies the time of reading as the number of milliseconds in the past.
• stale, basically a boolean with values of 0 or 1, defines if the reading is considered to be old (value being 1). If the data is stale, it means that there has been a problem with reading the sensor.

WiFi Configuration

GET /config?ssid=<SSID>&password=<PASSWORD> configures the board with a new SSID and an optional password. If you think why not a POST method, it is just because of pragmatic reasons. People who are not comfortable with curl and such tools, can simply use their browsers to enter the URL.

A Note on the WiFi Configuration Process

The main challenge with WiFi-based devices is how to configure the connection. The most common approach is that the device offers its own hotspot to which the user can connect and using an endpoint configure the device. Although, this seems very reasonable, in practice this is still not a very solid solution. So many times I had problems connecting to my boards, or having my laptop refusing to connect to the hotspot or later not being able to connect the board to my WiFi even with the correct password. A quick search shows that these are still common issues. That's why I aimed for a practical approach:

• The board can be pre-programmed with a fall-back WiFi connection. The good thing about it is that you can always make such a hotspot when needed. This is defined by the def_ssid and def_password constants.

• When the device comes up, it looks for a connection configuration. If there is a user-defined configuration, it tries to connect to the configured network. If the configuration is missing, or the connection cannot be established within 30 seconds, it falls back to the pre-programmed settings.

Old ESP8266 Chips

If you have older ESP8266 chips (I have quite a few), make sure that you update the firmware before programming them. Google will help you find the way, but if you have issues, just contact me and I will share with you what I know.

License

The code is published under an MIT license.

Contributions

Please report issues or feature requests using Github issues. Code contributions can be done using pull requests.