There are far too many one-off programming headers for Espressif MCUs. I wanted a simple programming header that I could use consistently across my projects, and I was surprised that there hasn’t been any consensus around a single header.
This is my attempt to specify a header format that can be used in future ESP8266 / ESP32 projects, and hopefully could even be adopted by companies that make popular products based on Espressif chips.
Whatever data source you want to record, there are a few common building blocks that you will need. Each of these building blocks has multiple alternatives. There are also totally different architectures that do things in a different way.
However, this particular combination of software is ideal for home automation, because these software building blocks can also be used for other purposes within your overall system.
You can install the various software elements on different computers, or in virtual machines, or using Docker containers, or on a NAS, or in many other ways.
To keep it simple and because many people already have one spare, we’re going to use a Raspberry Pi.
Prepare Raspberry Pi
Begin by installing Raspberry Pi OS (formerly known as “Raspbian”) on your Raspberry Pi. The easiest way to do it these days is to use the Raspberry Pi Imager, which runs on Windows, MacOS, or Linux and can be downloaded from www.raspberrypi.org/downloads/.
Use the Imager to download and install Raspberry Pi OS onto a micro SD card, insert it into your Pi, and start it up.
TODO: logging in first time.
Make sure your Pi has the latest packages by applying all updates:
sudo apt update sudo apt upgrade
You now have a Raspberry Pi with a basic Raspbian OS installation, ready for customisation.
Step 0: Get the IP address
We’ll need to know the IP address of the Raspberry Pi later. If you’ve connected using the hostname or you’re using a screen and keyboard, you can get the
Step 1: Install the Mosquitto MQTT broker and clients
There are many different MQTT brokers available, but Mosquitto is the most popular and it has served me well for many years. Install both the “mosquitto” package and the “mosquitto-clients” package, so that you have both the broker and some handy command line clients that you can use for testing:
sudo apt install mosquitto mosquitto-clients
The Mosquitto broker will be set up with a default configuration and will work fine out of the box, but we’re going to change the configuration to make it more secure.
You can leave your MQTT broker unprotected, but it’s a good idea to set a username and password on it.
First, create a text file that contains the username and password with a colon to separate them. You can do this on the command line with a single command:
echo "mqtt_username:mqtt_password" > pwfile
This will create a text file called “pwfile” with the details in them.
Use the passwd utility provided as part of the Mosquitto package to encrypt the file:
mosquitto_passwd -U pwfile
Display the contents of the file to verify that it has now been encrypted:
You will see your username in plaintext, followed by a string of gibberish which is the encrypted form of the password. If the password is still plaintext, it means the encryption command above didn’t work.
Move the encrypted file into the Mosquitto configuration directory:
sudo mv pwfile /etc/mosquitto/
Mosquitto needs to be told where the new file is located. Use an editor such as Nano to open the Mosquitto configuration file:
sudo nano /etc/mosquitto/mosquitto.conf
Near the bottom of the file, just above the “include_dir” line, add these lines:
To save your changes and exit, type CTRL+X, then Y, then ENTER.
The config change won’t be applied until InfluxDB has been restarted, so restart it manually:
sudo systemctl restart influxdb
From now on, any time you want to connect to the InfluxDB command line you will need to supply the username and password.
We need to do that now, so substitute the password you set:
influx -username admin -password <adminpassword>
If the previous changes worked, you should now be connected to InfluxDB again and authenticated as the admin user that you just created.
Next we need to tell InfluxDB to create a database where we can store sensor data. In this example I’ve simply called the database “sensors”:
CREATE DATABASE sensors
That was easy! Because of the way InfluxDB works, there’s no need to create a schema with tables and columns like you would be a relational database such as MariaDB, MySQL, Postgres, or SQL Server.
All you need to do is create an empty database, and it will be automatically populated when you start sending data to it.
Leave the InfluxDB client by typing exit, as before:
Step 3: Install Node-RED
There are several different ways to install Node-RED, and it’s readily available in the Raspbery OS packaging system. However, the Node-RED team recommend that you do NOT use the packaged version.
Instead, they provide a handy script that installs the latest version of Node-RED from the official release, and helps you keep it updated. The installation script goes far beyond that, however. It also:
makes sure there’s no existing installation of Node-RED and removes any that it finds in order to prevent conflicts
installs the latest Node.js
gives you the option of installing a set of useful nodes specifically designed to run on a Pi
sets up Node-RED to run as a service and installs tools to help you manage it
Before running the Node-RED installation script, install the tools needed by NPM to build binary modules:
sudo apt install build-essential git
Now you can run the official Node-RED installation script:
echo "deb https://packages.grafana.com/oss/deb stable main" | sudo tee -a /etc/apt/sources.list.d/grafana.list
Update the package list (again!) and install the Grafana package:
sudo apt update
sudo apt install grafana
Just like the other packages we've installed, we need to enable the service so that it will start automatically:
sudo systemctl enable grafana-server
That takes care of starting Grafana at boot. For now, let's start it manually:
sudo systemctl start grafana-server
Step 5: Configure your sensors to send data to MQTT
For each sensor that you want to log and report, you will need to go through a series of steps to ensure that the data is received by your Raspberry Pi, processed by Node-RED, stored in InfluxDB, and then charted using Grafana. This is a process that you will repeat multiple times as your build up your home automation system.
Let's break it down into a series of simple steps.
Begin watching MQTT for messages. There won't be any messages yet, but this is a handy technique for discovering new devices when they begin reporting to MQTT. On your Raspberry Pi, open a terminal and run the Mosquitto client command that we ran earlier:
This launches the Mosquitto client in "verbose" mode (the "-v" flag) and subscribes to all topics using the wildcard character. What this means is the client will display every message that is published by any client to any topic, and report not just the message but also the topic that it appeared in.
On a busy MQTT broker this is like drinking from a fire-hose!
However, we don't have any sensors using our MQTT broker yet so you shouldn't see anything happen: the terminal will just sit there waiting to display messages. Leave the terminal open so that you can see any messages that are published.
Configure sensor to report using MQTT. The exact process for this will depend on your device. Typically you will need to configure three things in your sensor:
The IP address (or hostname) of your MQTT broker. In this case, it's the IP address of the Raspberry Pi.
The username and password for MQTT. We configured this way back at the start of the process. If you don't have a username and password on your broker, you can skip this.
The MQTT topics for reporting. In many devices this should default to something sensible, and you may not need to change it. For our Air Quality Sensor project, the topic will be generated automatically based on the chip ID of the ESP chip.
If you are using the example Arduino sketch for the Air Quality Sensor, open it in the Arduino IDE and go to the tab called "config.h". Edit the broker IP address and the MQTT username / password to match your own settings:
Compile the sketch and flash it to the Air Quality Sensor, just like in the previous episodes.
After the sensor starts up with the new settings, you should see some action in the Mosquitto client! You'll see a startup message from the sensor, and then it will periodically begin publishing its readings.
Step 6: Receiving and storing single-value sensor readings
Step 7: Receiving and storing JSON-formatted sensor readings
Step 8: Create a dashboard and widgets in Grafana
You can access the Grafana user interface using a web browser, by connecting to port 3000 on your Raspberry Pi. The URL will look something like:
Substitute the IP address or hostname for your Raspberry Pi.
To log in, use the username and password "admin" and "admin". Grafana will ask you to change the password on first login, so set it to something secure.
If you order a “Wemos D1 Mini” you’d expect to get the same thing every time, right?
The Wemos brand has become a victim of counterfeiters, who make a near-exact copy of the board and then produce it as cheaply as they can. These two D1 Minis look superficially similar, and if they were lying on the bench you would probably have trouble telling them apart:
But look closer. The shape of the PCB is slightly different around the top edges, and the silkscreen is slightly different. It’s most obvious around the “5V” label near the bottom left. There’s also slightly different soldermask pullback around the pads. The board on the left has several parts out of alignment, although electrically they’re still connected and the board works fine.
Part of reducing the cost is to use whatever is the cheapest PCB substrate they can get their hands on at the time. These D1 Minis were made using totally different PCB material:
One PCB is 1mm thick, and the other is 1.6mm.
I’ve seen D1 Minis with 0.8mm, 1.0mm, 1.2mm, 1.4mm, and 1.6mm PCBs! You really can’t predict what you’re going to get.
Why does this matter?
Most of the time, it doesn’t. But recently I heard from someone trying to build my Air Quality Sensor project that their D1 Mini wouldn’t fit in the 3D printed case, because the case only allows PCBs up to 1.2mm thick! Oops.
So I’ve now generated STLs for both 1.2mm and 1.6mm slots, for both the “Basic” and “Display” versions of the case. You can grab the latest STLs from the product pages, linked from the respective episodes:
The ESP32 is a fantastic MCU, but when you are designing a project with it you need to choose the I/O pins very carefully.
Many of the I/O pins have special purposes, such as being bootstrapping pins that change the way the ESP32 boots up. Some have limitations, such as being OK to use as inputs but they don’t have pullup or pulldown resistors, so you have to bias them externally.
And some of the strange behaviour is really obscure: for example, you can’t use analog input on any pin associated with ADC2 while WiFi is in use!
To help me navigate these limitations I created a spreadsheet that lists the pins and their strange behaviour:
When I start a new project, I use this spreadsheet as a template and make a duplicate just for the project. Then I add notes to the “Purpose” column to say what I’m going to use each pin for.
I’ve made the template public, so you can make copies of it yourself for your projects. Click the preview above to open it in Google Sheets.
Many of the cells have notes attached to them, explaining specific limitations.
Because I mostly use Wroom32 modules, the spreadsheet has a column for Wroom32 pin numbers. You can change this to suit whatever module you use in your project, or ignore it and work from the direct ESP32 pin numbers which are also listed.
I needed PCB trays to keep boards organised during the production process, so I laser-cut a simple design.
The trays used by professional PCB assemblers are usually made from static-dissipative material that can also withstand immersion in an ultrasonic bath. My design isn’t intended as a replacement for those, but just as a handy way for hobbyists to keep small batches of boards organised on the workbench or shelves. This is much better than stacking populated PCBs on top of each other because it saves the parts and boards being scratched or damaged.
The Fusion360 file includes parameters so that you can tune the material thickness and the slot size to suit your own requirements. There is also a parameter for board width, but it’s broken at the moment.
DXFs have also been included, for 3mm MDF and 2mm PCB slots.
Some countries and services are not available, and the situation is changing by the day. As of today, there is a list of about 119 countries that I can’t ship to at all. For the rest, “Economy” class packages aren’t being processed, and for some classes of package there are delays of 2 to 5 weeks added to the normal shipping time.
If you add items to your cart and begin the checkout process, the online store will use your delivery address to determine if it’s possible to ship to you, and only offer you shipping methods that are currently available for your country.
So feel free to go ahead and place an order. I’m watching the situation very carefully and checking every order, so if there are any problems I’ll follow up with you.
For the latest status from Australia Post, you can check on their COVID-19 updates page:
Because of the decrease in international travel over the last couple of months, the postal service doesn’t have enough flights available to carry international letters and parcels.
As of this week, Australia Post can’t process “Economy” class international packages at all. Some premium classes of package, such as trackable services and International Express, are still being accepted at post offices. However, even these more expensive shipping options are experiencing weeks of delays.
Sadly, this means that I simply can’t ship international packages at the moment. I can still ship orders to Australian customers without any problems: domestic packages are being processed and transported as normal. It’s the lack of international flights that is the big problem.
I’ve now turned off all shipping methods for international customers.
The moment that the postal service has resumed international service, I’ll turn international shipping back on. Until then, I can only process orders for Australian customers.
You can build the Air Quality Sensor project without understanding how the software works, but if you want to know what’s really going on behind the scenes you can join me for a deep dive into the source code.