Electronics Fundamentals
The circuit basics every maker needs: Ohm’s law, resistors, capacitors, inductors, diodes, transistors and switches, with worked examples and diagrams.
Most maker projects need only a handful of ideas: how voltage, current and resistance relate, a few kinds of component, and a way to protect and switch them. This guide covers those basics in plain language, with worked numbers and diagrams, one component family at a time. It is the first of five Electronics guides: the others cover analog circuits and sensing, digital electronics and microcontrollers, power and motors, and design, testing and troubleshooting (listed at the end of this page). For joining parts and wire, see Soldering; to turn a working breadboard into a board, see PCB Design and Layout.
Start here: what do you need?
| I need to… | Go to |
|---|---|
| understand voltage, current, Ohm’s law, series and parallel, or read a schematic | Circuit Basics |
| read a resistor, choose a value or power rating, or add a pull-up | Resistors |
| choose a capacitor, decouple a chip, or time or filter a signal | Capacitors |
| protect a circuit from a coil’s spike, or choose a relay or transformer | Inductors, Transformers and Relays |
| pick a diode, build a rectifier, or choose an LED resistor | Diodes and LEDs |
| switch a motor, relay or LED strip from a microcontroller pin | Transistors |
| choose a switch, connector or fuse, or protect against a reversed supply | Switches, Connectors and Protection |
| join parts and wire permanently | Soldering |
| amplify a signal, compare voltages or use a 555 | Op-amps and Integrated Circuits |
| power a project from a battery, USB or a wall adapter | Batteries and Power Supplies |
A suggested order
If you are new to electronics, read the pages in this order. Each builds on the one before, and the previous and next links at the top and bottom of every page follow it.
- Circuit Basics: Voltage, current, resistance and power, Ohm’s law, series and parallel circuits, dividers, Kirchhoff’s laws, DC and AC, and how to read a schematic.
- Resistors: Fixed and variable resistors, the color code, standard values, power ratings, thermistors, light sensors, pull-ups and pull-downs.
- Capacitors: Ceramic, electrolytic, film and tantalum types, ratings, ESR, decoupling, and RC timing and filters.
- Inductors, Transformers and Relays: Inductance and flyback, chokes, transformers, and relays versus solid-state relays, with the protection each needs.
- Diodes and LEDs: Rectifier, Schottky, Zener and TVS diodes, bridge rectifiers, and LED types with current limiting.
- Transistors: Bipolar and MOSFET transistors as switches and amplifiers, base and gate resistors, and driving loads from a pin.
- Switches, Connectors and Protection: Switch types and ratings, connector families, fuses, reverse-polarity and surge protection, and wiring good practice.
Quick reference: formulas
| Topic | Formula | Page |
|---|---|---|
| Ohm’s law | V = I × R | Circuit Basics |
| Power | P = V × I = I² × R = V² ÷ R | Circuit Basics |
| Resistors in series, parallel | R1 + R2; R1R2 ÷ (R1 + R2) | Circuit Basics |
| Voltage divider | Vout = Vin × R2 ÷ (R1 + R2) | Circuit Basics |
| AC (RMS) | VRMS = Vpeak ÷ √2 | Circuit Basics |
| RC time constant | τ = R × C | Capacitors |
| RC cut-off frequency | fc = 1 ÷ (2π R C) | Capacitors |
| Capacitor energy | E = ½ C V² | Capacitors |
| Inductor | V = L dI/dt; E = ½ L I² | Inductors, Transformers and Relays |
| Transformer | V2 ÷ V1 = N2 ÷ N1 | Inductors, Transformers and Relays |
| LED resistor | R = (Vsupply − Vf) ÷ I | Diodes and LEDs |
| Rectifier ripple | ΔV ≈ I ÷ (2 f C) | Diodes and LEDs |
| BJT switch base resistor | RB = (V − 0.7) ÷ (IC ÷ 10) | Transistors |
A starter parts list
A small stock covers most first projects. All of these are inexpensive, and each is explained on the page named.
| Part | Suggested values or types | Page |
|---|---|---|
| Resistors | E12 assortment, ¼ W, 10 Ω to 1 MΩ; a few 1 % parts | Resistors |
| Ceramic capacitors | 100 nF (many), 10 nF, 1 nF, 22 pF | Capacitors |
| Electrolytic capacitors | 1 µF, 10 µF, 100 µF, 470 µF at 16–25 V | Capacitors |
| Diodes | 1N4148, 1N4007, 1N5819 Schottky; a few Zeners (3.3, 5.1 V) | Diodes and LEDs |
| LEDs | 5 mm red, green, yellow, white | Diodes and LEDs |
| Transistors | 2N2222A or BC337 (NPN), 2N2907 (PNP), IRLZ44N or AO3400 (logic-level N-MOSFET) | Transistors |
| ICs | LM358 or MCP6002 op-amp, NE555, LM393, 74HC595, 7805 and an LDO regulator | Op-amps and Integrated Circuits |
| Switches, headers, wire | Tactile buttons, 2.54 mm headers, jumper wires, hook-up wire in several colors | Switches, Connectors and Protection |
| Tools | Breadboard, multimeter, bench supply or USB supply, soldering station | Test Tools and Fault Finding |
Calculators
- Resistor Color Code Calculator: Read a four-, five- or six-band resistor, or find the bands for a value.
- Voltage Divider and LED Resistor Calculator: Output of a divider with and without a load, and the resistor for an LED.
- Ohm’s Law and Power Calculator: Any two of voltage, current, resistance and power give the other two.
- RC Time Constant and Filter Calculator: Time constant, cutoff frequency, filter gain and charging times.
- Resistor Network and Standard Value Calculator: Series and parallel totals, nearest E-series value, and a pair of standard resistors for a target.
- Reactance and Resonance Calculator: Capacitor and inductor reactance, resonant frequency and impedance.
Safety
- Mains voltage kills. Do not work on live mains equipment. Unplug, wait for capacitors to discharge, and test with a meter. If you are not competent, get a qualified person. See Workshop Safety.
- Batteries. Lithium cells can catch fire if shorted, damaged or overcharged. Use protected cells and the right charger, and never leave them charging unattended. See Batteries and Power Supplies.
- Use a current-limited supply the first time you power a new circuit.
- Wear safety glasses when powering new or repaired circuits and when clipping leads.
- Soldering has its own risks (burns, fumes, lead); see Soldering.
The other Electronics guides
- Analog Circuits and Sensing: Op-amps, comparators and timers, and how to read, amplify and filter sensor signals: thermistors, RTDs, load cells and 4-20 mA loops.
- Digital Electronics and Microcontrollers: Logic gates, counters and timing, and the hardware around a microcontroller: power, reset, clocks, GPIO, level shifting, the ADC and buses.
- Power and Motor Electronics: Batteries and supplies, switching converters and thermal design, and driving DC motors, steppers, servos and solenoids.
- Design, Testing and Troubleshooting: Reading datasheets, keeping a design quiet, measuring a circuit, finding faults with flowcharts, and complete worked projects.
- PCB Design and Layout: schematic to layout, stack-up, routing, return paths and design checks.
FAQ
Where should a complete beginner start?
Begin with Circuit Basics, then Resistors, Diodes and LEDs and Transistors. Build the circuits from the pages on a breadboard as you go: an LED with a resistor, a button with a pull-up, a transistor switch.
Do I need to learn the math?
Only a little: Ohm’s law and the power formula cover most hobby work, and both are in Circuit Basics. The other formulas are listed with worked examples so you can follow them step by step.
Which one tool should I buy first?
A multimeter. It finds most problems. A bench power supply with a current limit is the next most useful, followed by an oscilloscope when you start working with timing or noise. See Test Tools and Fault Finding.
Can I breadboard everything?
A breadboard is fine for testing low-frequency, low-current circuits. For anything permanent, high-current or noisy, move to a perfboard or a printed circuit board; see PCB Design and Layout.
References
- Platt, C., Make: Electronics, 3rd ed., Make Community.
- IEC 60062, Marking codes for resistors and capacitors; IEC 60063, Preferred number series (E-series).
- Horowitz, P. and Hill, W., The Art of Electronics, 3rd ed., Cambridge University Press.
- Manufacturer datasheets and application notes for the parts you use: they give the limits, pinouts and example circuits.
Last reviewed: October 2026. Values are typical: check the datasheets of the parts you use, follow the electrical code for mains work, and do not work on live mains equipment unless you are qualified.