The electronics under every board.
Why the LED died the instant you wired it. Why the pin reads 1.8 V when it should read 3.3. Why the board reboots every time the motor starts. These are the chapters that answer those — and because no chip is named and no code is printed, none of it stops being true when you change boards.
5 V across 220 Ω gives 22.7 mA, and 114 mW of heat in the resistor.
Contents
Every article, in order15 chapters and 12 courses. Start at the top, or go straight to the one with your part in it. A course is one card with every lesson in it, in order.
Volts, amps and ohms
Electricity · 3 articlesThe three numbers everything else is made of, the one equation that ties them together, and the schoolmaster who was called a fraud for finding it.
Resistors
Electricity · 4 articlesThe part you reach for most, in the four arrangements that cover almost every circuit.
LEDs
Electricity · 1 articleThe first thing everybody wires up, and the first thing everybody destroys.
Capacitors
Electricity · 5 articlesTwo plates and a gap nothing crosses. It blocks a steady voltage, passes a changing one, and every board you own has a dozen of them holding the rail up.
Powering the board
Electricity · 2 articles3.3 V against 5 V, and how much current the whole board actually draws.
Diodes
Electricity · 8 articlesThe part that only lets current through one way — charges about 0.7 V for the privilege, holds a fixed voltage when you push it backwards hard enough, and can be talked into storing a number.
Transistors and switching
Electricity · 4 articlesA pin can drive 20 mA. Everything bigger needs a part in between — three legs, two flavours, and one number to get right.
MOSFETs
Electricity · 4 articlesThe switch you turn with a voltage instead of a current. Four short pages, mostly moving pictures, ending with the one word on the datasheet that decides whether it works from a 3.3 V pin.
Inductors
Electricity · 4 articlesThe part that will not let its current change. Four pages on a coil of wire, what it stores, the rating that is not about heat, and the circuit the whole site has been telling you to use instead of a linear regulator.
Fuses and current limits
Power and protection · 2 articlesA short circuit is the load going to nearly zero ohms. Two parts stand between that and your supply, and they are not remotely equally fast.
Diodes and surge protection
Power and protection · 4 articlesA battery fitted backwards, two supplies feeding each other, and a spike arriving down the cable. Three problems, and four parts that answer them.
Lithium cells
Power and protection · 5 articlesThe only part on the bench that stores enough energy to hurt you, and the four chips people put in front of it.
Switching a rail
Power and protection · 1 articleA board asleep at microamps, and a module beside it that never sleeps at all. One chip cuts the module off completely, and costs nanoamps to do it.
Regulating a rail
Power and protection · 1 articleA lithium cell starts above 3.3 V and finishes below it. One chip bucks, then boosts, and holds the rail through the crossing, at 20 µA while the board sleeps.
I2C
Course · 12 lessons · 3D and VR · ▶ 12 filmsThe two-wire bus nearly every sensor module speaks, from the beginning. Every lesson has a bench in 3D and in a VR headset.
MQTT
Course · 10 lessons · 3D and VR · ▶ 10 filmsHow a reading gets from a sensor to a phone, a laptop and a lamp without any of them knowing the others. Every lesson has a bench in 3D and in a VR headset.
SPI
Course · 14 lessons · 3D and VR · ▶ 14 filmsThe four-wire bus that chip after chip uses when it needs to be fast: a clock, two belts of bits, and a light that says who is listening. Every lesson has a bench in 3D and in a VR headset.
Screens
Course · 16 lessons · 3D and VR · ▶ 16 filmsEvery way a screen is fed, from a two-wire OLED to an eDP laptop panel: how much data a picture is, where the picture lives, and what has to keep moving. Every lesson has a bench in 3D and in a VR headset.
- 01How much data is a screen4 min
- 02A screen is not one thing4 min
- 03I2C OLED4 min
- 04SPI TFT4 min
- 05QSPI displays4 min
- 068080 parallel4 min
- 07Where a frame lives4 min
- 08Frame buffer, PSRAM and DMA4 min
- 09RGB timing4 min
- 10RGB565, 666 and 8884 min
- 11Tearing and double buffering4 min
- 12MIPI DSI lanes4 min
- 13DSI command and video mode4 min
- 14LVDS4 min
- 15eDP4 min
- 16Start with your MCU4 min
TCP and UDP
Course · 12 lessons · 3D and VR · ▶ 12 filmsWhat a network adds to your data and what it leaves out: one-line cards that may be lost, and a novel cut into numbered strips that is pasted back together. Every lesson has a bench in 3D and in a VR headset.
- 01Why two ways to send4 min
- 02Which device, which app4 min
- 03UDP: one card, one try4 min
- 04What can happen on the way4 min
- 05TCP starts a connection4 min
- 06TCP is a byte stream4 min
- 07ACKs, resends and waiting5 min
- 08Flow control: the receiver's room4 min
- 09Congestion: the crowded desks5 min
- 10Finishing, half-close, reset4 min
- 11Choosing, and meeting QUIC4 min
- 12From the model to your ESP324 min
UART
Course · 12 lessons · 3D and VR · ▶ 12 filmsHow two devices send bytes down a wire with no clock between them, only an agreement made beforehand: the idle line, the start bit, the data bits, baud, and what happens when the two sides disagree. Every lesson has a bench in 3D and in a VR headset.
- 01Two wires, no clock4 min
- 02Idle high, then a start bit4 min
- 03The data bits, low bit first4 min
- 04Stop bit, parity and 8N15 min
- 05Baud: the speed you agree on4 min
- 06Sampling in the middle5 min
- 07When the settings disagree5 min
- 08The receive buffer4 min
- 09What the line can tell you4 min
- 10Asking the other side to wait5 min
- 11UART is not a voltage standard5 min
- 12From the model to your ESP324 min
RS-485 and Modbus
Course · 12 lessons · 3D and VR · ▶ 12 filmsHow a serial line is made to carry a long run and a crowd: a difference between two wires, a trunk with many taps, one driver at a time, the ends, and the Modbus conversation on top of it. Every lesson has a bench in 3D and in a VR headset.
- 01Two layers, one long line4 min
- 02A difference makes the bit4 min
- 03Noise that moves together4 min
- 04One trunk, many taps5 min
- 05One driver at a time4 min
- 06The quiet bus and its two ends5 min
- 07Who asks, who answers4 min
- 08The fields of a request5 min
- 09Four kinds of data5 min
- 10The manual's number trap4 min
- 11Silence closes the frame5 min
- 12Reply, exception or timeout5 min
CAN bus
Course · 12 lessons · 3D and VR · ▶ 12 filmsHow many devices share one pair of wires with no master: a hall of desks that shout or stay quiet, who speaks first, how a message is built and checked, what goes wrong, and the two ends of the rail. Every lesson has a bench in 3D and in a VR headset.
- 01Why one pair, and what the hall gets wrong4 min
- 02Two wires, one state4 min
- 03Labels, not addresses4 min
- 04Who speaks first4 min
- 05Staying in step4 min
- 06What a message looks like4 min
- 07Somebody heard4 min
- 08The stuffed bit4 min
- 09When a frame goes wrong5 min
- 10The two ends4 min
- 11How far, how fast, which ground5 min
- 12When nothing arrives5 min
Ethernet
Course · 12 lessons · 3D and VR · ▶ 12 filmsHow a cable carries a network: one shared channel and its collisions, what a frame holds and who it is for, hubs and switches, how a link comes up, the MAC, the PHY and RMII, and the three ways an ESP32 gets Ethernet. Every lesson has a bench in 3D and in a VR headset.
- 01Why plug in a cable?4 min
- 02One shared channel5 min
- 03What is inside a frame?5 min
- 04Who is this frame for?4 min
- 05From hubs to switches5 min
- 06How the link comes up4 min
- 07The MAC, the PHY and their wires5 min
- 08From frames to an IP address4 min
- 09Classic ESP32: built-in MAC, outside PHY5 min
- 10ESP32-S3: Ethernet over SPI5 min
- 11ESP32-P4: built-in MAC, no Wi-Fi radio4 min
- 12Choose a route, find the fault5 min
Wi-Fi
Course · 13 lessons · 3D and VR · ▶ 13 filmsHow a frame crosses the air: radio waves and channels, why signal is not a bar count, how a network is found and joined, station and access point, sharing airtime, hidden stations, robust versus fast, sleep and security, and the ESP32 on the bench. Every lesson has a bench in 3D and in a VR headset.
- 01A frame without a cable4 min
- 02Radio waves and channels5 min
- 03Signal is not a bar count4 min
- 04How a network is found4 min
- 05Joining has stages5 min
- 06Station, access point, or both5 min
- 07Sharing airtime5 min
- 08When stations cannot hear each other4 min
- 09Robust versus fast4 min
- 10A station that sleeps4 min
- 11Wi-Fi security in layers5 min
- 12The ESP32 on the bench5 min
- 13Connected, but nothing works5 min
LoRa
Course · 12 lessons · 3D and VR · ▶ 12 filmsSmall messages over a longer link: the chirp, spreading factor, bandwidth and coding, airtime, noise and interference, the rules where you live, collisions, a battery day, LoRa against LoRaWAN, and the ESP32 bench. Every lesson has a bench in 3D and in a VR headset.
- 01Small messages over a longer link4 min
- 02The chirp is the symbol4 min
- 03Spreading factor: time and sensitivity4 min
- 04Bandwidth, coding and the packet5 min
- 05Airtime is the real payload cost4 min
- 06Below the noise, not through interference5 min
- 07The rules where you live5 min
- 08Shared spectrum and collisions4 min
- 09A day in the life of a battery node5 min
- 10LoRa is not LoRaWAN4 min
- 11LoRaWAN's message rhythm and keys5 min
- 12On the ESP32 bench5 min
Zigbee
Course · 13 lessons · 3D and VR · ▶ 13 filmsA low-power mesh, not Wi-Fi: the shared radio, three roles, names and joining, paths, a sleepy sensor and its parent, clusters and bindings, security, the controller side, failure, and the ESP32 bench. Every lesson has a bench in 3D and in a VR headset.
- 01A low-power network, not Wi-Fi4 min
- 02The shared radio4 min
- 03Three roles4 min
- 04Names and temporary addresses4 min
- 05Joining and credentials5 min
- 06How paths form and change5 min
- 07Sleep, poll, deliver5 min
- 08What a device can do4 min
- 09Reports and direct actions5 min
- 10Security depends on setup5 min
- 11Zigbee, Thread, Matter and hubs5 min
- 12What happens when it fails?5 min
- 13On the ESP32 bench5 min
Making a through-hole joint, and telling a good one from the four kinds that fail.
Circuits, running
One block from a real board's schematic, redrawn and simulated. Open the lab to see it work, tap any part, and break it on purpose.
Or start from what went wrong
Most people arrive here angry. Pick what happened — each one is a two-minute read, not a course.
“My sensor reads random numbers.”
The pin is connected to nothing, so it reads your hand moving nearby.
Pull-up resistors →“I put 5 V into a 3.3 V pin.”
Sometimes nothing happens. Sometimes the pin dies three weeks later.
Logic levels →“My LED lit up once. Once.”
No resistor. It drew everything the pin could give, and that was that.
LED series resistor →“The board reboots when the motor starts.”
The motor eats the rail for a millisecond and the chip browns out.
Decoupling capacitors →“My battery lasts one day.”
Something is awake that should be asleep. Usually the regulator or an LED.
Power budget →“Nothing works and the wiring looks fine.”
Breadboards go bad. Four checks find it in under a minute.
Series and parallel →I²C, MQTT, SPI, screens, TCP and UDP, UART, RS-485 and Modbus, CAN bus, Ethernet, Wi-Fi, LoRa, and Zigbee have courses of their own, above. Looking for the board side of UART, or of Wi-Fi? They are chapters of the ESP32 book — same drawings, no board required: wires on the board and messages on the network.