Electronics 101

The Water Pipe Analogy

// USE THIS TO EXPLAIN VOLTAGE, CURRENT & RESISTANCE

Visualising the Three Fundamentals

VOLTAGE (V)

💧

Water Pressure The force pushing electrons around. Higher voltage = more push.

CURRENT (A)

💧

Flow Rate How many electrons pass a point per second. Measured in Amps.

RESISTANCE (Ω)

NARROW

Pipe Narrowing Restricts flow. More resistance = less current for same voltage.

Interactive Pipe — Change Two, See the Third

Lock any two sliders and watch the third value respond. The pipe diagram updates to show what's actually happening.

VOLTAGE (V) Water pressure

LOCK

1V9.0V20V

CURRENT (I) Flow rate

LOCK

1mA19mA100mA

RESISTANCE (R) Pipe width

LOCK

10Ω470Ω2kΩ

💡 Lock two values to see how the third must change

The Key Insight

If you increase the pressure (voltage) without changing the pipe narrowing, more water (current) flows.

If you narrow the pipe more (increase resistance), less water (current) flows for the same pressure.

These three things are always connected — change one, and another must change. That relationship is Ohm's Law.

Ohm's Law

// V = I × R — THE ONLY EQUATION YOU NEED TODAY

The Triangle

V = I×R

To find Voltage:
multiply Current × Resistance

I = V÷R

To find Current:
divide Voltage by Resistance

R = V÷I

To find Resistance:
divide Voltage by Current

Live Calculator — Try It

VOLTAGE (V) — volts

CURRENT (I) — amps

RESISTANCE (R) — ohms

Fill in any two fields — the third will be calculated automatically

Real-World Example: Choosing an LED Resistor

You have a 9V battery. Your LED needs 2V and 20mA (0.02A).
The resistor must drop the remaining 7V (9V − 2V = 7V).

R = V ÷ I = 7 ÷ 0.02 = 350Ω → use a 390Ω (next standard value up)

Power

// P = I × V — WHY COMPONENTS HAVE RATINGS

What is Power?

Power (measured in Watts) is the rate at which energy is used. Every component has a maximum power rating — exceed it and it gets hot, then breaks.

P = I × V or P = I² × R or P = V² ÷ R

USB Port Power Budget — Interactive

0W used of 10W

⚠ OVER LIMIT — port will cut out

CLICK A DEVICE TO SEE ITS DRAW:

Series vs Parallel

// HOW YOU CONNECT COMPONENTS CHANGES EVERYTHING

Current is the same through every component

Voltage is shared — each component gets a portion

Resistance adds up: R_total = R1 + R2 + R3…

If one component fails open, the whole circuit breaks (Christmas lights)

Voltage is the same across every branch

Current splits between branches (more paths = more total current)

Resistance decreases overall: 1/R_total = 1/R1 + 1/R2…

If one branch fails, others keep working (house wiring)

Component Tour

// CLICK ANY COMPONENT TO LEARN MORE

Reading Schematics

// A MAP OF YOUR CIRCUIT — SAME CIRCUIT, TWO VIEWS

LED + Resistor Circuit — Schematic vs Real World

SCHEMATIC (standard symbols)

BREADBOARD (real world)

Common Schematic Symbols

Battery / PowerLong line = +, short line = −. Often stacked pairs of lines.

ResistorZigzag (US) or rectangle (EU). Limits current flow.

LEDTriangle pointing to bar. Arrows show light emitting.

CapacitorTwo parallel lines (or one curved). Stores charge briefly.

Ground (GND)Downward triangle or three shrinking lines = return path.

Wire junctionA dot where wires cross = connected. No dot = wires pass over.

LM386 Audio Amplifier

// YOUR BUILD GUIDE — BEGINNER FRIENDLY, STEP BY STEP

What Are We Building?

A mono audio amplifier. You plug your phone into it via a 3.5mm headphone jack, and it drives a small speaker loud enough to fill a room. Everything is powered from a USB cable — the same kind of power that charges your phone.

At the heart of it is a single chip: the LM386. It takes a tiny audio signal from your phone (just millivolts) and amplifies it to a level that can push a speaker cone back and forth. Everything else in the circuit is there to support that chip — clean power, controlled gain, protecting the speaker, adjusting the volume.

🔌

POWER IN

5V via USB-A
from any phone charger

🎵

AUDIO IN

Stereo 3.5mm jack
summed to mono

🔊

AUDIO OUT

8Ω 0.5W speaker
driven by LM386

🎚️

VOLUME

10kΩ potentiometer
controls input level

Before you start: You've already used resistors, capacitors, and potentiometers on the breadboard today. Every component in this build is something you've already seen — this circuit just combines them in a more purposeful way. If anything looks unfamiliar, the Components tab has a plain-English explanation of every part.

Circuit Schematic — Click Any Component to Learn More

↑ Click any component on the schematic to learn what it does

Every Component — What It Is & Why It's Here

Click any card to expand the explanation. These are in the order you'll place them on the board.

Build Order

Always solder lowest-profile components first — they're hardest to reach once taller parts are in place. Work through this list in order.

IC Socket (8-pin DIP)

Solder the socket, NOT the chip. The notch on the socket marks pin 1 — match it to your layout. Soldering the chip directly risks heat damage and makes it impossible to replace if something goes wrong.

Resistors — R1, R2, R3, R4

Resistors have no polarity — either way round is fine. Bend the legs to fit the holes, push through, splay slightly on the back to hold in place, solder, trim. R1 and R2 are both 10kΩ (brown-black-orange). R3 is 1.2kΩ (brown-red-red). R4 is 10Ω (brown-black-black).

Ceramic Capacitors — C3, C4, C7

Small disc or MLCC caps. No polarity — either way round. C3 is 47nF (marked 473). C4 and C7 are 0.1µF (marked 104). These are small and easy to place before the taller electrolytics go in.

Electrolytic Capacitors — C1, C2, C5, C6

⚠ POLARITY MATTERS. The longer leg is positive (+). The negative leg has a stripe on the body. Get these wrong and they can fail or even burst. C1 is 10µF. C2 is 250µF (positive leg toward the chip). C5 is 470µF. C6 is 100µF. Both C5 and C6 have positive legs toward +5V.

Potentiometer — RV1

The volume pot. Three pins: left pin and right pin are the ends of the resistor track, middle pin is the wiper. Middle pin connects to the LM386 input. One end pin connects to the summing node (from R1/R2), the other end pin to GND. Check your reference build before soldering.

3.5mm Jack & USB Cable

Solder the jack to the board — tip is left channel, ring is right, sleeve is GND. For the USB cable, strip the outer sheath, find the red (+5V) and black (GND) wires, ignore the white and green data wires. Tin the ends before soldering to the board.

Speaker Wires

Solder two wires to the speaker terminals, then solder the other ends to the board output points. Speaker polarity is not critical for mono — it affects the direction the cone moves but won't damage anything if reversed.

Insert the LM386 Chip — Last

Press the chip into the socket. The notch or dot on the chip marks pin 1 — align it with the notch on the socket. Legs may need gently straightening first. Press evenly and firmly. Do not power up until the chip is seated fully.

Before powering up: visually inspect every joint. Check for bridges (solder blobs connecting two pins that shouldn't be). Check electrolytic capacitor polarity. Check the chip is the right way round. A multimeter continuity check between +5V and GND should show no connection — if it beeps, you have a short somewhere.

Testing Your Build

① Power check — before audio

Plug in USB. Measure voltage between pin 6 (VS) and pin 4 (GND) on the chip — you should read close to 5V. If you read 0V, check your USB wiring. If the board gets warm immediately, unplug — you likely have a short.

② Touch test

With power on and volume turned up, touch the tip of the 3.5mm jack with your finger. You should hear a hum from the speaker — your body is acting as an aerial, picking up mains interference. If you hear hum, the signal path is working.

③ Plug in a source

Plug a phone in via the 3.5mm jack, play music, turn up the volume pot. You should hear clear audio. Rotate the pot from minimum to maximum and confirm volume changes smoothly with no crackling.

④ Common faults

No sound at all — check chip orientation, check C2 polarity, check speaker connections.

Loud hiss or squeal — check the Zobel network (R4 + C3), check decoupling caps C6 and C7 are in place.

Very low volume — check R3 and C1 (gain components between pins 1 and 8), check pot wiper is wired to pin 3.

Crackling / distortion — check C2 is 250µF and correctly polarised. Check supply voltage hasn't drooped — try a different USB charger.

The multimeter is your best friend here. If something isn't working, don't guess — measure. Check voltages at each pin against what they should be. Continuity-check your signal path from jack tip all the way through to the speaker. Most faults in a first solder build are either a cold joint (reflow it), a bridge (wick it off), or a component in backwards (desolder and flip it).

Perfboard Layout

This is a top-down view of your perfboard showing exactly where each component goes. Toggle between the top view (component side — what you see while placing parts) and the bottom view (solder side — where you make the connections). Hover over any component to highlight it.

+5V rail GND rail Audio signal Volume/input Chip connections Output/speaker

Wire Link Guide

On perfboard, holes in the same row/column are NOT connected — you must bridge them yourself with short wire links or by bending component legs. These are the connections to make on the solder side.

+5V Rail
Run a wire along the top row from the USB red wire pad all the way right to the VS pin (pin 6) of the chip socket. Also tap off to the + legs of C5 and C6.

GND Rail
Run a wire along the bottom row from the USB black wire pad all the way right. Connect: USB −, C5 −, C6 −, C7, chip pin 4, chip pin 2, pot low end, jack sleeve, C3/R4 bottom, C2 speaker side −, speaker −.

L+R to R1/R2
Jack tip (L) → R1 input. Jack ring (R) → R2 input. Both R1 and R2 outputs meet at one node — bridge those two holes with a short wire link.

Summing node → Pot → Pin 3
Summing node to pot high end. Pot wiper to chip pin 3. Pot low end to GND rail. Three short wire links.

Gain loop: Pin 1 → C1 → R3 → Pin 8
Chip pin 1 → C1 positive leg. C1 negative leg → R3. R3 other end → chip pin 8. These can be routed directly above the chip using bent component legs.

Bypass: Pin 7 → C4 → GND
Chip pin 7 → one leg of C4. Other leg of C4 to GND rail. Short link, keep it close to the chip.

Output: Pin 5 → C2 → Speaker+
Chip pin 5 → C2 positive leg (polarity critical). C2 negative leg → speaker + wire. Speaker − wire → GND rail.

Zobel: Pin 5 → R4 → C3 → GND
Tap from the same node as pin 5. R4 in series with C3 (no polarity on C3), bottom of C3 to GND. Keeps the output stable.

Breadboard Circuits

// FOUR STEPS — ONE EVOLVING BUILD — CLICK EACH STEP TO EXPAND

Each circuit below builds on the last — don't dismantle, just add. By step 4 you have a light-sensitive circuit with a real sensor, a visual readout, and a switch. Clip your component voltmeter across key parts as you go and watch the readings change.

Step 1 — LED + Resistor

The most fundamental circuit. Current flows from the battery, through the resistor (which limits how much flows), through the LED (which converts that current to light), and back to ground. Without the resistor the LED would draw too much current and burn out instantly.

Calculate the resistor first: Battery = 9V. LED needs ~2V. Remaining voltage = 7V. Target current = 20mA (0.02A). R = V ÷ I = 7 ÷ 0.02 = 350Ω → use 390Ω (next standard value up).

SCHEMATIC

What to build
+ terminal → 390Ω resistor → LED anode (long leg) → LED cathode (short leg) → GND

Voltmeter exercise
Clip across the LED: reads ~2V. Clip across the resistor: reads ~7V. Add them: 9V. That's Kirchhoff's Voltage Law — voltage around a loop always sums to zero.

Common mistake
LED in backwards — it just won't light. Flip it. No damage done at these current levels.

Visualising the Three Fundamentals

Interactive Pipe — Change Two, See the Third

The Key Insight

The Triangle

Live Calculator — Try It

Real-World Example: Choosing an LED Resistor

What is Power?

USB Port Power Budget — Interactive

LED + Resistor Circuit — Schematic vs Real World

Common Schematic Symbols

What Are We Building?

Circuit Schematic — Click Any Component to Learn More

Every Component — What It Is & Why It's Here

Build Order

Testing Your Build

Perfboard Layout

Wire Link Guide

Step 1 — LED + Resistor

Step 2 — Add a Potentiometer

Step 3 — Button, then Switch

Step 4 — LDR Light Sensor