First Little Project with ESP32 - WiFi Kit 32 OLED/BLE

Taking the First Steps - ESP32 - WiFi Kit 32 OLED/BLE
Attempting to build something useful

As per my previous post I have an opportunity to utilize these ESP32 modules in projects, so I thought I'd start with something pretty straightforward. In this case, I'll be using both ESP32 modules and a DHT22 temperature and humidity sensor, all provided by DigitSpace, to manage a few tasks:

1. Get and display the current date/time
2. ESP #1 get and display the current household temperature and humidity
3. Pass the Temp/Humidity info to ESP#2
4. ESP#1 Download current weather information and display it using the OLED
5. ESP#1 Download local daily Covid19 stats and display it using the OLED
6. ESP#2 receive the info from ESP#1 and alert via LED and OLED if temp/humidity out of range

The overall goal here is to create something useful while running the devices through some general tasks that test out the operation and programming for the things I am most interested in here, the WiFi and the OLED display.


2xESP32 WiFi Kit 32 w/OLED
1xDHT22 Temperature/Humidity sensor

Note: The ESP modules come with the pins separate, you will need a soldering iron to connect them.

Setting Up The IDE & Software:

1. Install the ESP32 Arduino Core per the installation instructions for Arduino Boards Manager
2. Select Heltec WiFi Kit 32 for the board
3. I chose the U8g2lib for the OLED display. It is available via Arduino Library Manager

Getting it All Up and Running

Graphics Library:

I started out with just the U8g2lib for the OLED, choosing the font group, font size etc, and figuring out basically how to use it. In this case, with the font I chose, I can fit five lines of 20 characters onto the screen, so I created 5 character arrays, and have them drawn on screen every loop. Then it is just a matter of loading the buffers with whatever information I want displayed.

For that, I created a simple function to take in a char array along with its length and the intended line number to display it on. Then all I have to do is put data in the buffers at any given time, and it gets displayed on screen. This may be over-complicating things a bit, but there is no messing about with what to refresh, what lines to draw etc, just put data in the buffers and it gets drawn.

Current Date/Time:

This part was surprisingly easy. It is a matter of specifying an NTP server or pool of servers, the GMT and DST offsets, then calling a standard time function to retrieve the information as desired.

WiFi Connectivity, HTTPS/SSL:

There are a number of examples and tutorials regarding getting connected to WiFi itself, so I'll leave that part out.

The client and SSL/HTTPS connectivity is nice to have, but seems to be a bit painful, since you apparently need to grab the certificate for the root authority of the site in question and put it in your code in order to establish a connection.

In order to grab the certificate, I found the easiest way is with a simple Linux command:
openssl s_client -showcerts -connect <hostname>:443

Beyond that, I pretty much followed the tutorial found here for setting up SSL/HTTPS connections.

It seems that once connected to a host via SSL, the ESP32 will continue to use the certificate as specified, since in order to connect to a second website for information,  I had to use SSL and specify the root_ca cert for the second site, even though I could have connected without SSL. I'm still looking into how to clear that from memory and allow normal connections etc.

The DHT22 Sensor:

This step was pretty simple also. The sensor itself connects to 3.3v, GND and any suitable GPIO pin. There is a DHT library specifically for the ESP32 available in the Arduino IDE with included examples.

The Modules in Operation:

The main module will grab information from the internet on startup, time/date, weather and covid19 stats for the local area.
The date/time and household temperature & humidity are constantly displayed on screen and updated regularly.
The bottom portion of the screen alternates between weather and covid19 information every 10 seconds.
The weather is updated every hour, and daily covid19 data refreshed every 6 hours.

The secondary module will receive the humidity and temperature sensor data from the main module as it is refreshed via http get request. If out of range a message will display on screen, and the onboard LED will flash. Users can disable the flashing LED by querying http://<IP-OF-ESP32>/s
An 's' character will stop the alerting, any other character will resume.

A video of the modules in operation is below:

The onboard LED does not show up well in the video because of the light on the camera. The OLED text was too bright and blurry on screen without the light, so it was a bit of  a compromise.


This was a nice project to work on with some opportunities to try a few new things, learn some things and mess around with some new hardware. The code itself could be cleaned up a bit and fine tuned, since I didn't pay much attention to conserving memory or program space, but there is more than enough to handle the tasks at hand.

I think I'll keep the main device in operation, and maybe look at updating the code to handle additional tasks & processing. I think the secondary device could easily be an AVR based device with an audible alerting system, using RF24 for data transfer. It is nice to have the ESP32, but it seems a bit overkill for the situation.

This was a good way to test and get used to having the OLED display and WiFi capabilities on hand to do with whatever is needed. All in all I'm really liking these devices. More to come with ESP32 projects and development!


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