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 13 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 order13 chapters. Start at the top, or go straight to the one with your part in it.
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.
Making a through-hole joint, and telling a good one from the four kinds that fail.
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 →Looking for I²C, SPI, UART, Wi-Fi or MQTT? They are chapters of the ESP32 book — same drawings, no board required: wires on the board and messages on the network.