Electron21
Build circuits, emulate processors, analyse data and engineer ideas. The lab for electronics, computer engineering, data science and engineering.
Pick a field. Start building.
Every field has its own labs, projects and cheat sheets. Click a card to jump straight to the right tools.
Meet the electron
Every circuit, chip and screen in this lab runs on one tiny particle. Here is what it is, how it behaves in a wire, and how it grew into the computer in your pocket.
e⁻.Electrons in a copper wire
Each electron drifts very slowly, yet a lamp lights at once. The electric field travels along the wire at a large fraction of the speed of light and pushes every electron together, like water already filling a pipe.
Electron, proton, neutron
| Particle | Charge | Mass | Where |
|---|---|---|---|
| Electron | −1 | 9.11 × 10−31 kg | Around the nucleus |
| Proton | +1 | 1.673 × 10−27 kg | In the nucleus |
| Neutron | 0 | 1.675 × 10−27 kg | In the nucleus |
Why it matters in electronics
- Conductors (copper, silver, gold) have loosely held outer electrons that move freely.
- Insulators (rubber, glass, plastic) hold their electrons tightly, so current cannot flow.
- Semiconductors (silicon has 4 outer electrons) can be switched between the two. That is how a transistor works.
- Conventional current is drawn from + to −, the opposite way to the electrons. Benjamin Franklin chose it more than a century before the electron was found, and every circuit diagram still uses it.
- Electron volt (eV) is the energy of one electron moved through 1 volt: 1.602 × 10−19 J. Silicon needs about 1.12 eV to free an electron.
From one electron to your phone
- The electron is discoveredJ. J. Thomson shows that cathode rays are streams of tiny negative particles.
- The vacuum tubeJohn Ambrose Fleming invents the diode, the first device that controls the flow of electrons.
- The transistorBardeen, Brattain and Shockley build it at Bell Labs: a tiny switch with no glass tube and no hot filament.
- The integrated circuitJack Kilby puts several parts on one piece of semiconductor at Texas Instruments.
- The microprocessorIntel's 4004 packs about 2,300 transistors onto one chip. It was a 4-bit CPU, a small cousin of the 8-bit one in the CPU Emulator.
- Tens of billionsA modern processor holds tens of billions of transistors, each one switching electrons billions of times a second.
Seven labs. Zero installs.
Real simulators and emulators that run in your browser. Flip switches, write assembly, load a CSV. Nothing is uploaded; everything stays on your device.
Open the workbench on its own page
Free course · 24 lessons
Learn it in the course. Try it in the lab.
Our free Electronics for Beginners course has 5 modules and 24 lessons. Electron21 is its hands-on partner: the key lessons link straight to the lab that lets you try the idea yourself.
- Module 2The laws of the circuit
- Module 3Meet the components
- Module 4Reading and building circuits
- Module 5Digital electronics and projects
Projects you can actually build
Thirty step-by-step projects across all four fields, from a first blinking LED to a temperature-controlled fan and a crop-yield prediction model. Each lists the parts, the steps and what you will learn.
The cheat sheets engineers keep open
Compact references for formulas, components, protocols and workflows.
Ohm's law & power
| Find | Formula |
|---|---|
| Voltage V | V = I × R |
| Current I | I = V ÷ R |
| Resistance R | R = V ÷ I |
| Power P | P = V × I = I²R = V²/R |
| Series | R = R1 + R2 + … |
| Parallel | 1/R = 1/R1 + 1/R2 + … |
| Divider | Vout = Vin × R2 ÷ (R1 + R2) |
| RC time constant | τ = R × C |
Boolean algebra & gates
| Law | Expression |
|---|---|
| Identity | A·1 = A A+0 = A |
| Null | A·0 = 0 A+1 = 1 |
| Complement | A·A' = 0 A+A' = 1 |
| De Morgan | (A·B)' = A'+B' (A+B)' = A'·B' |
| Absorption | A + A·B = A |
| XOR | A⊕B = A·B' + A'·B |
NAND and NOR are universal gates: any digital circuit can be built from either one alone.
Common components
| Part | Job |
|---|---|
| Resistor | limits current, sets voltages |
| Capacitor | stores charge, smooths and filters |
| Diode / LED | current flows one way (LED also lights) |
| Transistor | a switch or amplifier controlled by a small signal |
| 555 timer | makes pulses and delays |
| Op-amp | amplifies the difference between two inputs |
| Microcontroller | tiny computer: reads sensors, drives outputs |
UART, I²C and SPI
| UART | I²C | SPI | |
|---|---|---|---|
| Wires | 2 (TX, RX) | 2 (SDA, SCL) | 4+ (MOSI, MISO, SCK, CS) |
| Devices | point to point | many, by address | many, one CS each |
| Speed | slow to medium | 100 k–400 kHz+ | fastest (MHz) |
| Clock | none (async) | shared | shared |
| Typical use | GPS, serial console | sensors, OLED | SD card, displays |
Number systems
| Dec | Bin | Hex | Dec | Bin | Hex |
|---|---|---|---|---|---|
| 0 | 0000 | 0 | 8 | 1000 | 8 |
| 1 | 0001 | 1 | 9 | 1001 | 9 |
| 2 | 0010 | 2 | 10 | 1010 | A |
| 3 | 0011 | 3 | 11 | 1011 | B |
| 4 | 0100 | 4 | 12 | 1100 | C |
| 5 | 0101 | 5 | 13 | 1101 | D |
| 6 | 0110 | 6 | 14 | 1110 | E |
| 7 | 0111 | 7 | 15 | 1111 | F |
Two's complement: to negate, invert all bits and add 1. In 8 bits, 11111111 = −1.
Data science workflow
- Ask a clear question.
- Collect data, with permission.
- Clean: fix missing values, duplicates, units.
- Explore: summary stats and charts.
- Model: start simple (average, then regression).
- Validate on data the model has not seen.
- Communicate findings and their limits.
Engineering design process
- Define the problem and constraints (cost, time, safety).
- Research existing solutions.
- Brainstorm several ideas, then choose one.
- Prototype a small version.
- Test against clear measurements.
- Improve and repeat. Iteration is the method.
Lab safety rules
- Use batteries or low-voltage USB (5 V). Never experiment with mains electricity.
- Work with an adult when using a soldering iron, hot glue or tools.
- Never short-circuit a battery, especially lithium cells.
- Always add a resistor in series with an LED.
- Disconnect power before changing wiring.
Go deeper with full courses
Electronics for Beginners
The free companion course: 5 modules and 24 lessons from Ohm's law to logic gates and the 555 timer.
Start the course →AI & Machine Learning
Seven modules from data and models to neural networks and ethics.
Start the course →Smart21Code
Write and run code in your browser with guided tutorials.
Open Smart21Code →Circuit game
Learn how current flows by solving electric-circuit puzzles.
Play now →System21 tools
Free everyday tools: QR codes, converters, PDF and image utilities.
Open the tools →Build. Simulate. Understand.
Pick a lab and make something happen in the next five minutes.