Electronics course: 19 interactive lessons

The simplest useful circuit there is: a battery, a switch, a resistor and a light (an LED). Every torch and every power light on a gadget works this way.

Two resistors connected in a line (series) or side by side (parallel). These two patterns are the building blocks of every circuit diagram.

One resistor connected to a battery. It shows the most important rule in electronics, Ohm’s law, and why real parts get hot and can burn out.

Two batteries feeding one shared resistor. Real circuits are networks like this, and two simple laws let you work out every current in them.

A real battery has a small resistance inside it. This lesson shows why a battery’s voltage drops (sags) when you draw a lot of current, as when a phone dies in the cold.

Two resistors that turn 5 V into a smaller voltage. This is how a microcontroller measures a voltage that is too big for its input.

A capacitor charging and discharging through a resistor. This is how circuits make time delays, like a light that fades out slowly.

A resistor and capacitor used as a filter that lets low notes through and blocks high ones (or the other way round). Audio tone controls work like this.

A relay coil switched on and off by a transistor. Coils hate sudden stops, and this lesson shows the huge voltage spike that can kill the transistor — and the diode that prevents it.

Diodes are one-way valves for electricity. LEDs are diodes that glow. This lesson shows how to give an LED exactly the right current.

A MOSFET used as an electronic switch, so that a small microcontroller pin can turn a big load (a motor or LED strip) on and off.

The op-amp is a tiny amplifier chip. Here it is used as a buffer, a comparator and an amplifier — three jobs you find in nearly every sensor circuit.

How a microcontroller reads a push button. A bare input pin “floats” and reads random noise, and real buttons bounce.

Two ways a chip can drive a wire: push-pull (actively high and low) or open-drain (only pulls low). Shared data buses like I²C use open-drain.

What digital communication looks like on an oscilloscope: an I²C message to a temperature sensor, and PWM that dims an LED.

Two ways to turn 12 V into 3.3 V for a chip. One burns the extra as heat, the other switches cleverly and wastes very little.

The protection parts at the input of a gadget that save it from being plugged in backwards, from static zaps and from short circuits.

How to read a datasheet to work out whether a part will overheat. Heat flows out of a chip a lot like current flows through resistors.

Copper tracks on a circuit board are not perfect wires. Too thin, and they heat up and waste voltage.