Electronics from Zero: Voltage, Current and the Transistor as a Switch
Every digital circuit is built on a little physics: charge flowing round a loop, pushed by a voltage and held back by resistance. This course starts there and assumes nothing. You will work out currents with Ohm's law, time circuits with capacitors, light LEDs safely, switch loads with transistors, see how a logic gate is made from them, and read the datasheets and schematics of real parts. Every value in it was computed from the circuit you see.
Start here
Start with Volume 00. It explains what electronics is, what voltage and current mean in plain words, how the course works and how to stay safe. Then take the volumes in order - each one uses only what came before it.
This course assumes nothing. You do not need any maths beyond multiplying and dividing, and you do not need any parts: every circuit is drawn and worked out on the page.
Every voltage, current and power in these lessons was computed by a circuit solver from the very circuit drawn beside it, so a number can never disagree with its drawing. Each new word is underlined with dots - point at it (or tap it) to see what it means - and every sub-module ends with a quick check.
Electronics is the ground under every other course here. When you finish, go on to Digital Logic from Zero, which builds with the gates this course makes from transistors, or to Embedded C from Zero, which drives LEDs, motors and sensors from a microcontroller.
Full syllabus
Part I - The basics
- 00 Start Here: What Electronics Is What electronics is, charge, current and voltage in plain words, how this course works, and how to stay safe. Live
- 01 Voltage, Current and Resistance Charge and current, voltage, resistance and resistors, reading resistor values from their colour bands, and measuring with a multimeter. Live
- 02 Ohm's Law, Power, Series and Parallel Ohm's law, power and energy, resistors in series and the voltage divider, resistors in parallel and the current divider, and Kirchhoff's laws. Live
Part II - Parts that store and steer
- 03 Capacitors, Inductors and RC Timing How capacitors store charge, charging and discharging through a resistor, RC filters, inductors, and debouncing a switch. Live
- 04 Diodes and LEDs The diode as a one-way valve, LEDs and their series resistor, protecting a circuit from a reversed battery, rectifiers, and Zener diodes. Live
Part III - Switching with transistors
- 05 Transistors as Switches Why switch with a transistor, the bipolar transistor and the MOSFET as switches, driving motors and relays safely, and pull-up and pull-down resistors. Live
- 06 From Transistor to Logic Gate (CMOS) NMOS and PMOS transistors as switches, the CMOS inverter, CMOS NAND and NOR gates, why CMOS uses so little power, and logic levels. Live
Part IV - Real circuits
- 07 Power Supplies, Regulators and Decoupling Batteries and their capacity, linear and switching regulators and the heat they make, decoupling capacitors, and ground and return paths. Live
- 08 Datasheets, Schematics and Bench Tools Reading schematics and datasheets, using a multimeter, an oscilloscope and a logic analyser, and a first build on a breadboard. Live
What you need before starting
| What | Why | Free option |
|---|---|---|
| Nothing but curiosity | Volume 00 starts from the very beginning | - |
| A calculator | Most of the work is multiplying and dividing | The one on your phone |
| Optional: a circuit simulator | To build the circuits yourself and watch the numbers change | Falstad's circuit simulator runs in a web browser |
| Optional: a starter kit | To build on a breadboard | A breadboard, a 9 V battery or 5 V supply, some resistors, LEDs and a multimeter - the course never needs one |