Post it once. Everyone who asked gets a copy.
MQTT is a post office for devices: a sensor posts to a topic, and the post office delivers a copy to everyone who subscribed. Ten short lessons, each with a bench you can press, on a laptop, a phone or in a VR headset.
Why devices post to a broker instead of to each other, what goes on the envelope, and who gets a copy.
A whole room or a whole house with one subscription, and the last letter kept for whoever connects late.
Ordinary letters, registered mail and signed-for mail: QoS 0, 1 and 2, and why each hop has its own.
How the broker knows a device is still there, what it says when one vanishes, and who it lets in.
Electricity
Volts, current, resistance and the mistakes that kill parts. 35 pages, true of every board.
35 articles →The other fundamentals trackPower and protection
Fuses, ideal diodes, TVS and lithium cells — every part that sits between a supply and something you would rather not replace. 13 pages, with part numbers.
13 articles →The other fundamentals trackI2C
The two-wire bus nearly every sensor module speaks, from the beginning. Every lesson has a bench in 3D and in a VR headset.
12 articles →The other fundamentals trackWorkshop
The hand skills. Soldering a joint that lasts, and reading the ones that will not. 2 pages, no circuit required.
2 articles →Next, in the ESP32 bookWires on the board
How two chips agree on what a line means, sorted by what it costs you in pins
9 articles, no board required →Next, in the ESP32 bookMessages on the network
Once there is no wire left to agree about, the question is who talks first
5 articles, no board required →