Basic Electronics — Complete Course

COMPLETE COURSE MAP

Electronics Course Overview

A structured journey from the very first question — "What is electricity?" — all the way to building smart electronic projects. Designed for students in Grades 5 through 10, with content that scales in complexity as the course progresses.

UNIT 01

⚡ Electricity Basics

What is electricity?
Atoms, protons & electrons
Conductors & insulators
Static electricity
Electrical safety rules

🎓 Grade 5–6 friendly

UNIT 02

📐 Ohm's Law & Power

Voltage — electrical pressure
Current — electron flow
Resistance — opposition
Ohm's Law: V = I × R
Power: P = V × I

🎓 Grade 6–7 friendly

UNIT 03

🔌 Circuit Types

Open & closed circuits
Series circuits
Parallel circuits
Mixed (series-parallel)
Voltage & current rules

🎓 Grade 6–8 friendly

UNIT 04

🔩 Passive Components

Resistors + color code
Capacitors (charge/discharge)
Inductors & coils
Transformers
Component ratings & datasheets

🎓 Grade 7–8 friendly

UNIT 05

💎 Semiconductors

Diodes & rectification
LEDs & forward voltage
NPN & PNP transistors
Transistor as switch/amplifier
Logic gates (AND, OR, NOT)

🎓 Grade 8–9 friendly

UNIT 06

📡 Sensors & Actuators

LDR — light sensor
Thermistor — temperature
Piezo buzzer & speaker
DC motor & polarity
Relay for high-power control

🎓 Grade 8–9 friendly

UNIT 07

🔧 Tools & Techniques

Using a multimeter
Breadboard layout & wiring
Reading circuit schematics
PCB basics & traces
Soldering safety

🎓 Grade 9–10 ready

UNIT 08

🛠️ Projects & Capstone

Auto Night Light (LDR + LED)
Touch Alarm (transistor)
Water Level Indicator
Temperature Alert
Capstone: Your own design

🎓 Grade 7–10 builds

📚 HOW THIS COURSE WORKS

🎯 Grade Scaling

Each topic includes content at three levels: Grade 5–6 (visual & analogy), Grade 7–8 (formulas introduced), and Grade 9–10 (full technical depth).

⚡ Animated Diagrams

Every topic features technically accurate SVG animations — proper schematic symbols, correct electron flow direction, real component behavior visualized live.

🛠️ Hands-On Projects

Month 8 brings everything together into 5 buildable projects plus a student-designed capstone. Each project lists all components, circuit diagram, and step-by-step instructions.

🔢 Interactive Calculators

Ohm's Law calculator, Resistor color-code decoder, and circuit simulators let students explore concepts by changing values and seeing immediate results.

LESSON 1

What is Electricity?

Electricity is a form of energy caused by the movement of tiny particles called electrons. It powers everything around us — from light bulbs to smartphones — and understanding it starts with one simple question: what makes electrons move?

ELECTRONS FLOWING THROUGH A WIRE

💡 SIMPLE ANALOGY — WATER IN A PIPE

🚰 Water = Electric Charge

Just like water consists of water molecules, electricity consists of electrons. Both flow from one place to another and can do useful work.

🏔️ Water Tower = Battery

A water tower stores water and creates pressure. A battery stores chemical energy and creates electrical pressure (called Voltage).

🚿 Water Flow = Current

How much water flows per second through a pipe is like current — the number of electrons passing a point per second.

🪵 Narrow Pipe = Resistance

A narrow pipe slows water down. Resistance slows electrons down. Materials like copper have low resistance; rubber has very high resistance.

📖 Grade 5–6: Think of electricity as "invisible water" that flows through wires. The battery is the pump. The wire is the pipe. The light bulb is the water wheel that uses the flow to make energy!

🌍 WHERE DO WE USE ELECTRICITY?

Light: LED bulbs, tube lights, streetlights — electricity excites electrons in materials to produce photons (light particles).
Heat: Electric stoves, geysers, irons — electricity flows through high-resistance materials generating heat (Joule heating).
Motion: Electric fans, motors, trains — electricity creates magnetic fields that produce mechanical motion.
Sound: Speakers, buzzers, headphones — electricity makes a membrane vibrate, creating sound waves.
Information: Phones, computers, internet — very small electrical signals carry coded data at nearly the speed of light.

LESSON 2

Atoms & Electrons

Everything in the universe — including you, this screen, and the wires in the wall — is made of atoms. Understanding the structure of an atom is the foundation of understanding why electricity exists.

COPPER ATOM — 29 ELECTRONS (SIMPLIFIED)

⚛️ PARTS OF AN ATOM

Particle	Location	Charge	Role in Electricity
Proton (p⁺)	Nucleus (center)	Positive (+)	Stays fixed. Determines what element the atom is.
Neutron (n)	Nucleus (center)	None (neutral)	Stays fixed. Adds mass to the nucleus.
Electron (e⁻)	Orbits (shells)	Negative (−)	Can move between atoms. This movement IS electricity!

🔑 Key Idea: Copper has 29 electrons. The outermost one (called the valence electron) is held very loosely — it can easily escape and jump to the next copper atom. This is why copper is an excellent conductor!

📖 Grade 9–10: Materials with 1–3 valence electrons are conductors. Materials with 4 valence electrons are semiconductors (silicon, germanium). Materials with 5–8 valence electrons are insulators.

🔢 HOW MANY VALENCE ELECTRONS? (COMMON MATERIALS)

Material	Valence Electrons	Type	Example Use
Copper (Cu)	1	Excellent Conductor	Wires, PCB traces
Silver (Ag)	1	Best Conductor	High-end contacts
Gold (Au)	1	Conductor (no rust)	Circuit board contacts
Silicon (Si)	4	Semiconductor	Transistors, ICs, solar cells
Rubber	8	Insulator	Wire coating, gloves
Glass	8	Insulator	Bulb cover, fiber optics

LESSON 3

Conductors & Insulators

Not all materials allow electricity to flow through them. Conductors let current flow freely. Insulators block current. A third class — semiconductors — can do both depending on conditions. This property is called electrical conductivity.

CONDUCTOR vs INSULATOR — ELECTRON BEHAVIOR

📊 CONDUCTOR vs SEMICONDUCTOR vs INSULATOR

Property	Conductor	Semiconductor	Insulator
Free electrons	Many (very free)	Few (controllable)	Almost none
Resistivity	Very low	Medium	Very high
Examples	Copper, Silver, Gold, Aluminium	Silicon, Germanium	Rubber, Glass, Plastic, Air, Wood
Used for	Wires, connectors	Transistors, solar cells, ICs	Wire insulation, cases
Can be controlled?	No	Yes (by doping, heat, light)	No

🧲 SPECIAL CASES TO KNOW

Carbon (graphite): A non-metal that IS a conductor! Used in pencil "lead" and electrodes. Carbon has a special bonding structure that lets electrons move freely.
Water: Pure water is an insulator. But water with dissolved salts (like seawater or tap water) is a conductor — the ions carry charge. This is why you should NEVER touch electrical things with wet hands.
Superconductors: Some materials at very low temperatures (near −273°C) have ZERO resistance. Current flows forever with no energy loss!
Doped semiconductors: By adding tiny amounts of other elements (called "dopants") to silicon, we can make it conduct or not — this is how transistors and computer chips work.

LESSON 4

Static Electricity

Static electricity happens when electric charges build up on a surface but don't flow anywhere — they are "static" (not moving). When the built-up charge suddenly discharges, you feel a spark or see lightning!

STATIC CHARGE BUILDUP — BALLOON & HAIR

⚡ HOW STATIC ELECTRICITY BUILDS UP

Friction: When two materials rub together, electrons transfer from one to the other. The material that gains electrons becomes negatively charged; the one that loses them becomes positive.
Induction: A charged object brought near a neutral object can attract or repel charges without touching — this temporarily charges the neutral object.
Discharge: When the built-up charge gets large enough, electrons jump through air to equalize the difference — this is a spark or lightning bolt.

⚡ Lightning Facts: A single lightning bolt can reach 30,000 Kelvin (5× hotter than the sun's surface!) and carries about 1 billion Volts of potential difference. It lasts only 0.2 seconds but transfers enormous energy.

📱 Everyday Static: Rubbing a comb on your hair, touching a door handle after walking on carpet, clothes clinging in a dryer, balloon sticking to a wall — all static electricity!

LESSON 5

Electrical Safety

Electricity is incredibly useful but can be dangerous if mishandled. Even low voltages like 50V AC or the 230V from a wall socket can be lethal. These safety rules could save your life.

🛡️ CRITICAL SAFETY RULES — NEVER BREAK THESE

Never touch live wires with bare hands. Always switch off the mains before working on household wiring. In Nepal, household voltage is 230V AC — this WILL kill if you touch it.
Keep water away from electricity. Water (especially tap water with minerals) conducts electricity. Never touch switches, sockets, or devices with wet hands.
Don't insert objects into sockets. The holes in a wall socket are directly connected to high-voltage power lines. This is extremely dangerous.
Always use the correct fuse or circuit breaker. Fuses protect circuits by breaking if too much current flows. Using the wrong (higher) fuse removes this protection.
In the lab, work only below 30V DC. For school experiments, always use batteries (9V, 12V) or regulated power supplies. Never work directly with mains (230V).
Switch off before connecting/disconnecting components. Always power off your circuit before adding or removing wires or components to avoid short circuits or component damage.

⚠️ What to do if someone is being electrocuted: DO NOT touch them! Switch off the power immediately. If you can't switch off, use a non-conducting object (dry wood, plastic chair) to push them away from the live source. Call emergency services (100 in Nepal).

🔌 UNDERSTANDING DANGER LEVELS

Voltage	Source	Danger Level	Notes
1.5V	AA/AAA Battery	Safe	Cannot cause electric shock; short circuits get hot
9V	PP3 Battery	Safe	You might feel a tingle if you lick the terminals!
12V	Car battery / Power supply	Low risk	Won't shock through dry skin; but can cause sparks/fire
48V	Some power supplies	Caution	Can cause mild shock; avoid direct contact
230V AC	Wall socket (Nepal)	⚠️ LETHAL	Can stop heart. NEVER touch with bare hands. EVER.
1000V+	Power lines / Lightning	⚠️ INSTANTLY FATAL	Stay far away from fallen power lines

LESSON 1

Voltage — Electrical Pressure

Voltage is the "electrical pressure" that pushes electrons through a circuit. Measured in Volts (V), it represents the difference in electrical potential energy between two points. Without voltage, electrons have no reason to move.

WATER PRESSURE ANALOGY — HIGHER TANK = MORE VOLTAGE

🔋 COMMON VOLTAGE VALUES

Source	Voltage	Type	Used For
Small cell battery (AAA/AA)	1.5V	DC	Toys, remotes, small devices
9V block battery	9V	DC	Experiments, smoke detectors
Phone charger output	5V	DC	USB, Arduino, Raspberry Pi
Car battery	12V	DC	Automotive, LED strips
Household socket (Nepal)	230V	AC (50Hz)	All home appliances
Power transmission lines	11,000V – 400,000V	AC	Grid transmission

DC vs AC: DC (Direct Current) flows in one direction only — like a battery. AC (Alternating Current) reverses direction 50 times per second (50 Hz in Nepal). Your home uses AC because it's easier to transmit over long distances at high voltage.

LESSON 2

Current — Electron Flow

Electric current is the rate at which electric charge flows past a point in a circuit. Measured in Amperes (A), it tells you how many electrons are moving per second. One Ampere = 6.24 × 10¹⁸ electrons per second!

📊 CURRENT UNITS

Unit	Symbol	Value	Used For
Ampere	A	1 A	Large loads — motors, heating elements
Milliampere	mA	0.001 A (1/1000 A)	Most electronic circuits — LEDs, transistors
Microampere	µA	0.000001 A	Sensors, microcontrollers in sleep mode

⚠️ Body Danger: It's not Voltage that kills directly — it's Current. As little as 10mA through your heart can cause ventricular fibrillation (irregular heartbeat), and 100mA can be fatal. The reason high voltage is dangerous is because it drives large current through your body's resistance.

📖 Conventional vs Electron Current: Historically, scientists assumed current flowed from + to −. Later, electrons were discovered to actually flow from − to +. We still use "conventional current" (+ to −) in circuit diagrams by convention — be aware of this difference!

LESSON 3

Resistance — Opposition to Flow

Every material opposes the flow of electrons to some degree. This opposition is called Resistance, measured in Ohms (Ω). Higher resistance means less current flows for the same voltage. Resistance converts electrical energy into heat.

HIGH vs LOW RESISTANCE — PIPE WIDTH ANALOGY

🌡️ FACTORS THAT AFFECT RESISTANCE

Material (Resistivity ρ): Copper has very low resistivity (1.7×10⁻⁸ Ω·m). Nichrome (heating element wire) has 100× more. Each material has a fixed resistivity value.
Length (L): Longer wire = more resistance. Resistance is directly proportional to length: R ∝ L. Double the length → double the resistance.
Cross-sectional Area (A): Thicker wire = less resistance. R ∝ 1/A. Double the thickness → half the resistance.
Temperature: For most metals, resistance increases with temperature (positive temperature coefficient). For semiconductors like silicon, resistance DECREASES with temperature.

R = ρ × L / A

ρ = material resistivity (Ω·m) | L = wire length (m) | A = cross-sectional area (m²)
Grade 9–10: This explains why power lines use thick aluminium cables!

LESSON 4

Ohm's Law

Ohm's Law is the most fundamental equation in electronics. It states that the voltage across a component equals the current through it multiplied by its resistance. Discovered by Georg Ohm in 1827, it governs every resistive circuit.

V = I × R

V = Voltage in Volts | I = Current in Amperes | R = Resistance in Ohms
Rearrange: I = V ÷ R | R = V ÷ I

🔢 OHM'S LAW INTERACTIVE CALCULATOR

Enter any TWO values — the third will be calculated automatically. Leave one field empty.

VOLTAGE (V)

Volts

CURRENT (I)

Amperes

RESISTANCE (R)

Ohms

💡 Example: LED circuit with 9V battery and 330Ω resistor → Current = 9 ÷ 330 = 27.3 mA. This is the current through your LED!

📐 OHM'S LAW TRIANGLE — MEMORY TRICK

Cover V: V = I × R (current times resistance)
Cover I: I = V ÷ R (voltage divided by resistance)
Cover R: R = V ÷ I (voltage divided by current)

LESSON 5

Power Formula

Electrical power is the rate at which electrical energy is converted to other forms (heat, light, motion). Measured in Watts (W), it tells you how much energy a component uses per second. Your electricity bill is based on power usage over time!

P = V × I = I² × R = V² ÷ R

P = Power (Watts) | V = Voltage (V) | I = Current (A) | R = Resistance (Ω)
1 Watt = 1 Joule of energy per second | 1 kWh = 1000W running for 1 hour

💡 REAL-WORLD POWER EXAMPLES

Device	Voltage	Current	Power	Cost to Run 8hrs/day
LED bulb	230V	26mA	6W	~NPR 0.5/day
CFL bulb	230V	48mA	11W	~NPR 0.9/day
Fan (ceiling)	230V	0.35A	80W	~NPR 6/day
Electric iron	230V	4.3A	1000W	~NPR 80/day
Air conditioner	230V	8.7A	2000W	~NPR 160/day

Energy = Power × Time: 1 kWh (kilowatt-hour) = 1000W × 1 hour. This is the unit on your electricity bill. In Nepal, it costs approximately Rs. 9–13 per kWh. A 100W bulb left on for 10 hours uses 1 kWh.

LESSON 1

Open Circuit

An open circuit has a break (gap) somewhere in the path. Since there is no complete loop, electrons cannot flow — no current, no light, no function. The component is effectively disconnected from the power source.

OPEN CIRCUIT — SWITCH OPEN, NO CURRENT

🔍 CAUSES OF OPEN CIRCUITS

Open switch: Deliberately breaking the circuit to stop current — a light switch, for example.
Broken wire: A wire that has been cut or has snapped internally. Current cannot cross the gap.
Blown fuse: The fuse wire melts when excess current passes through, deliberately creating an open circuit to protect the circuit.
Loose connection: A component leg not properly seated in a breadboard hole. Looks connected but isn't making contact.
Burned out component: A bulb's filament or an LED that has blown open internally.

LESSON 2

Closed Circuit

A closed circuit is a complete, unbroken loop from the positive terminal, through all components, back to the negative terminal. Current flows, and components do their job — lights glow, motors spin, buzzers beep.

CLOSED CIRCUIT — SWITCH CLOSED, CURRENT FLOWS

LESSON 3

Series Circuit

In a series circuit, all components are connected end-to-end in a single loop. There is exactly one path for electrons to travel. The same current flows through every component, but voltage divides proportionally across each one.

SERIES CIRCUIT — SAME CURRENT, VOLTAGE DIVIDES

📐 SERIES CIRCUIT RULES

R_total = R₁ + R₂ + R₃ + …

Current is SAME everywhere: I = V_total ÷ R_total
Voltages ADD UP: V₁ + V₂ + V₃ = V_source (Kirchhoff's Voltage Law)

Voltage Divider: Each resistor "grabs" a portion of the total voltage proportional to its resistance. V₁ = I × R₁, V₂ = I × R₂, etc.
Failure mode: If any component opens (breaks), the ENTIRE circuit stops. This was the problem with old Christmas lights!
Grade 9–10 — Kirchhoff's Voltage Law (KVL): The sum of all voltage drops around a closed loop equals the source voltage. This is conservation of energy applied to circuits.

LESSON 4

Parallel Circuit

In a parallel circuit, components are connected across the same two nodes, providing multiple independent paths for current. Each branch operates independently — same voltage across all branches, current divides between them.

PARALLEL CIRCUIT — SAME VOLTAGE, CURRENT SPLITS

📐 PARALLEL CIRCUIT RULES

1/R_total = 1/R₁ + 1/R₂ + 1/R₃

Voltage is SAME across all branches: V₁ = V₂ = V₃ = V_source
Currents ADD UP: I_total = I₁ + I₂ + I₃ (Kirchhoff's Current Law)

Independent operation: If one branch fails (opens), the others continue working. This is why household wiring is parallel — your fan works even if a bulb blows.
Total resistance decreases: Adding branches gives more paths, reducing total resistance. For N equal resistors of value R: R_total = R/N.
Higher current demand: More branches means more total current drawn from the source. Too many parallel loads can blow a fuse.

🏠 Home wiring is parallel: Every socket in your house is connected in parallel. Each device gets the full 230V. Turning one off doesn't affect others. Adding more devices increases total current — which is why circuit breakers are essential.

LESSON 5

Mixed (Series-Parallel) Circuits

Real-world circuits are rarely pure series or pure parallel — they are combinations of both. Analyzing mixed circuits requires breaking them into recognizable series and parallel sections and solving step by step.

🔢 HOW TO SOLVE MIXED CIRCUITS (GRADE 9–10)

Step 1 — Identify parallel groups: Find components sharing the same two nodes (same start and end points). These are in parallel.
Step 2 — Simplify parallel groups: Calculate equivalent resistance for each parallel group using 1/R_eq = 1/R₁ + 1/R₂...
Step 3 — Redraw the circuit: Replace each parallel group with its single equivalent resistor. Now you have a simpler series circuit.
Step 4 — Solve the series circuit: Add all remaining resistances. Use Ohm's Law to find total current.
Step 5 — Work backwards: Use the total current and the equivalent resistances to find voltages and currents in each original branch.

Example: R1 (100Ω) in series with a parallel group of R2 (200Ω) ∥ R3 (200Ω).
Step 1: R2∥R3 = 100Ω. Step 2: R_total = R1 + 100 = 200Ω. Step 3: I_total = 9V ÷ 200Ω = 45mA. Step 4: V_R1 = 45mA × 100 = 4.5V, V_parallel_group = 4.5V. Step 5: I₂ = I₃ = 4.5V ÷ 200 = 22.5mA each.

LESSON 1

Resistors & Color Code

A resistor is a passive two-terminal component that opposes current flow by a fixed amount. It is the most common component in electronics, used to limit current, divide voltage, and set operating points for active components.

Resistor

PASSIVE — CURRENT LIMITING — PRECISION

Resists electron flow. Dissipates energy as heat. Available from 0.1Ω to 10MΩ. Rated by resistance value, tolerance (accuracy), and power rating (max heat dissipation in Watts).

±1%

High Precision

±5%

Standard

0.25W

Typical Power

E24

Value Series

📊 TYPES OF RESISTORS

Type	Symbol	Adjustable?	Common Use
Fixed Resistor	—/\/\/—	No	Current limiting, voltage dividers
Variable Resistor (Rheostat)	—/\/\/—→	Yes (2 terminals)	Fan speed control, lamp dimmers
Potentiometer (POT)	—/\/\/—↕	Yes (3 terminals)	Volume knobs, joysticks
LDR (Light Dependent R)	R + light symbol	By light	Automatic lights, light sensors
Thermistor (NTC)	R + T symbol	By temperature	Thermometers, temperature control

🎨 RESISTOR COLOR CODE CALCULATOR

Select a color for each of the 4 bands to read the resistor value. The color code system lets you identify any resistor by its painted stripes.

BAND 1 (1st digit)

BAND 2 (2nd digit)

BAND 3 (multiplier)

BAND 4 (tolerance)

1 kΩ

Tolerance: ±5% | Range: 950 Ω – 1.05 kΩ

LESSON 2

Capacitors — Charge & Discharge

A capacitor stores electrical energy in an electric field between two conductive plates separated by an insulator (dielectric). Unlike a battery, it charges and discharges very quickly — in milliseconds. Measured in Farads (F).

CAPACITOR CHARGING — PLATES ACCUMULATE CHARGE

🔵 CAPACITOR KEY FACTS

C = Q / V | E = ½ × C × V²

C = Capacitance (Farads) | Q = Charge stored (Coulombs) | V = Voltage across capacitor
E = Energy stored (Joules) — charge a 1000µF cap to 12V → stores 0.072J of energy

Blocks DC, passes AC: Once fully charged, a capacitor blocks DC (no more current flows). But AC alternates direction — the cap continuously charges and discharges, effectively "passing" AC signals.
Time constant (τ = RC): How long it takes to charge to ~63% of supply voltage. τ = R × C. At 5τ it's essentially fully charged. (Grade 9–10)
Electrolytic capacitors are polarized: They have a + and − leg. Connect the + leg to the higher voltage. Reverse connection can damage or even explode the capacitor!
Applications: Power supply filtering (smoothing voltage), coupling (passing AC between amplifier stages), decoupling (removing noise from power supply), timing circuits, camera flash storage.

Type	Typical Range	Polarized?	Use
Ceramic disc	1pF – 100nF	No	Decoupling, RF filtering
Film (polyester)	1nF – 10µF	No	Precision, audio circuits
Electrolytic (aluminium)	1µF – 10,000µF	Yes (+/−)	Power supply filtering
Supercapacitor	0.1F – 3,000F	Yes	Energy storage, backup power

LESSON 3

Inductors — Coils & Magnetism

An inductor is a coil of wire that stores energy in a magnetic field when current flows through it. It opposes changes in current. Measured in Henries (H), inductors are key components in power converters, filters, and radio circuits.

INDUCTOR — CURRENT CREATES MAGNETIC FIELD

🌀 HOW AN INDUCTOR WORKS

Electromagnetic induction: When current flows through a coil, it creates a magnetic field. When current changes, the changing field induces a voltage in the coil that opposes the change (Lenz's Law).
Passes DC, blocks AC: Opposite to a capacitor! DC passes through freely (just the wire resistance). High-frequency AC is blocked because the inductor continuously opposes the changing current.
Energy storage: Stored energy E = ½LI². When the current is cut, the inductor releases this energy — this can cause a large voltage spike that damages transistors! (Always use a flyback diode.)
Applications: Power supply chokes, LC oscillators (radio tuning), transformers, relay coils, motor windings, wireless charging coils.

📡 Radio Tuning: In an LC (Inductor-Capacitor) circuit, the resonant frequency is f = 1 / (2π√LC). By adjusting L or C, you tune to different radio stations — this was the basis of all early radio receivers!

LESSON 4

Transformers

A transformer uses electromagnetic induction to transfer electrical energy between two coils (primary and secondary) without direct electrical contact. It can step voltage UP or DOWN while conserving power. The basis of all AC power distribution.

📐 TRANSFORMER FORMULA

V_primary / V_secondary = N_primary / N_secondary

N = number of turns in each coil | V = voltage | I = current
Also: I_primary / I_secondary = N_secondary / N_primary (power is conserved: P_in ≈ P_out)

Step-up transformer: More turns in secondary than primary. Increases voltage, decreases current. Used in power transmission (11kV → 132kV) to reduce I²R losses in long cables.
Step-down transformer: More turns in primary. Reduces voltage. Your phone charger has a step-down transformer converting 230V to 5–20V.
Only works with AC: A transformer needs changing magnetic flux, so it only works with alternating current. DC produces a static field — no induction.

Example: Primary has 2300 turns at 230V. Secondary has 100 turns. Secondary voltage = 230 × (100/2300) = 10V. If primary draws 0.1A, secondary current = 0.1 × (2300/100) = 2.3A. Power in = Power out = 23W.

LESSON 1

Diodes — One-Way Current

A diode is a semiconductor device that allows current to flow in only one direction — from Anode (+) to Cathode (−) in forward bias. It blocks current in reverse bias. Like a one-way valve for electricity.

DIODE — FORWARD BIAS (LEFT) vs REVERSE BIAS (RIGHT)

📊 TYPES OF DIODES

Type	Forward Voltage	Special Feature	Use
Signal diode (1N4148)	0.7V	Fast switching	Logic circuits, signal clipping
Rectifier diode (1N4007)	0.7V	High current (1A)	Power supply rectification (AC→DC)
Zener diode	Breakdown V	Conducts in reverse at set V	Voltage regulation
LED (Light Emitting)	1.8–3.5V (color dep.)	Emits light	Indicators, displays, lighting
Schottky diode	0.2–0.3V	Very fast, low forward V	Power converters, RF circuits

LESSON 2

LEDs — Light Emitting Diodes

An LED is a semiconductor diode that emits light when forward-biased. When electrons recombine with holes at the p-n junction, they release energy as photons. The color of light depends on the semiconductor material and its bandgap energy.

LED

LIGHT EMITTING DIODE — SEMICONDUCTOR

Forward-biased PN junction that converts electrical energy directly to light (electroluminescence). 90% more efficient than incandescent bulbs. Longer anode leg = positive terminal.

2V

Red V_f

2.1V

Yellow/Green V_f

3.2V

Blue/White V_f

20mA

Typical I_f

R = (V_supply − V_f) / I_f

Always use a series resistor to limit current! Example: 9V supply, red LED (V_f=2V), I_f=20mA
R = (9−2) / 0.020 = 350Ω → use 330Ω (nearest standard value)

LED Color	Forward Voltage (V_f)	Semiconductor Material
Red	1.8 – 2.1V	Gallium Arsenide Phosphide (GaAsP)
Orange / Yellow	2.0 – 2.2V	GaAsP or GaP
Green	2.0 – 3.5V	GaP (old) or InGaN (modern)
Blue	3.0 – 3.5V	Indium Gallium Nitride (InGaN)
White	3.0 – 3.5V	Blue LED + yellow phosphor coating
Infrared (IR)	1.2 – 1.5V	GaAs — invisible to human eye

LESSON 3

Transistors — BC547 NPN

A transistor is a semiconductor amplifier and switching device with three terminals: Base (B), Collector (C), and Emitter (E). A small current at the Base controls a much larger current from Collector to Emitter — making it the core of all modern electronics.

NPN TRANSISTOR — BASE SIGNAL CONTROLS COLLECTOR LOAD

🔺 BC547 NPN TRANSISTOR — PINOUT & SPECS

Flat Side Facing You

Left pin = Collector, Middle pin = Base, Right pin = Emitter. Always check datasheet — some transistors have different pinouts!

Current Gain (β or hFE)

BC547 has β = 100–800. This means 1mA of base current can control up to 800mA of collector current. For safe operation, use a base resistor.

Switching Mode

If V_BE > 0.6V, transistor turns ON (saturates). If V_BE < 0.6V, transistor is OFF (cut-off). Used to switch LEDs, buzzers, relays.

Amplification Mode

In the active region, I_C = β × I_B. Used in audio amplifiers, sensor circuits. The transistor acts as a current-controlled current source.

β = I_C / I_B | R_base = (V_supply − 0.6) / I_B

To fully switch ON an LED (I_C = 20mA) with β=200, you need I_B = 20/200 = 0.1mA minimum.
R_base = (9 − 0.6) / 0.001 = 8.4kΩ → use 10kΩ (gives headroom for reliable saturation)

LESSON 4

Logic Gates

Logic gates are the building blocks of digital electronics. They perform Boolean operations on binary inputs (HIGH = 1 = ~5V, LOW = 0 = 0V). Every computer, microcontroller, and digital device is built from billions of these gates.

🧠 THE THREE BASIC GATES

Gate	Symbol Logic	Truth Table	Meaning	IC
AND	A · B = Y	0·0=0, 0·1=0, 1·0=0, 1·1=1	Output HIGH only when ALL inputs are HIGH	7408
OR	A + B = Y	0+0=0, 0+1=1, 1+0=1, 1+1=1	Output HIGH when ANY input is HIGH	7432
NOT (Inverter)	Ā = Y	0→1, 1→0	Output is always OPPOSITE of input	7404
NAND	NOT(A·B)	0·0=1, 0·1=1, 1·0=1, 1·1=0	Opposite of AND — universal gate	7400
NOR	NOT(A+B)	0+0=1, else 0	Opposite of OR — universal gate	7402

Universal Gates: NAND and NOR gates alone can be combined to create ANY other logic function. All modern processors use primarily NAND gates internally — billions of them in a single chip!

Real-world example: An AND gate is like a lock with TWO keys — both must be present to open. An OR gate is like a door with TWO handles — either one opens it.

LESSON 1

LDR — Light Dependent Resistor

An LDR (also called a photoresistor) changes its resistance based on light intensity. In darkness, resistance is very high (1MΩ). In bright light, resistance drops drastically (100–500Ω). Used in automatic lights, cameras, and solar trackers.

LDR — RESISTANCE CHANGES WITH LIGHT

🌙 LDR VOLTAGE DIVIDER CIRCUIT (Used in Auto Night Light)

V_out = V_cc × R_fixed / (R_LDR + R_fixed)

In darkness: R_LDR=1MΩ, R_fixed=10kΩ → V_out = 9 × 10k/(1010k) ≈ 0.09V (LOW)
In light: R_LDR=300Ω, R_fixed=10kΩ → V_out = 9 × 10k/(10.3k) ≈ 8.74V (HIGH)
This voltage change triggers a transistor to switch a load ON or OFF!

⚡ In auto night light: Dark → R_LDR high → V_out low → transistor OFF → LED OFF.
Bright → R_LDR low → V_out high → transistor base activated → LED ON.
Reverse the component order to get light-activated vs dark-activated behavior.

LESSON 2

Thermistor — Temperature Sensor

A thermistor is a resistor whose value changes significantly with temperature. NTC (Negative Temperature Coefficient) thermistors decrease in resistance as temperature rises. PTC (Positive) increases. Used in thermometers, temperature controls, and motor protection.

🌡️ NTC vs PTC THERMISTORS

Type	Behavior	At 25°C	At 100°C	Use
NTC 10kΩ	R decreases as T rises	10,000Ω	~600Ω	Temperature measurement, thermostats
PTC	R increases as T rises	Low	Very high	Overcurrent protection, self-resetting fuses

Steinhart-Hart Equation (Grade 9–10): The relationship between temperature and NTC thermistor resistance is: 1/T = A + B·ln(R) + C·ln(R)³. For engineering accuracy, always calibrate your thermistor against a reference thermometer at known temperatures.

Voltage divider circuit: Connect thermistor in series with a known resistor. Read the voltage at the midpoint. As temperature changes, so does the voltage — which you can measure or feed to a comparator.
Fire alarm: NTC thermistor in a circuit — when fire heats it, R drops, voltage changes, triggering an alarm transistor.
Body temperature: NTC thermistors sensitive to 0.01°C are used in digital clinical thermometers.

LESSON 3

Buzzer & Speaker

A buzzer converts electrical energy into sound. Piezoelectric buzzers use a crystal that deforms when voltage is applied, creating vibrations. Electromagnetic buzzers use a coil and magnetic membrane. Speakers use a voice coil in a magnetic field.

🔔 TYPES OF SOUND OUTPUT DEVICES

Device	Working Principle	Frequency Range	Wiring
Piezo buzzer (active)	Built-in oscillator; just apply DC	Fixed (2–4kHz)	+ and −, 5–12V
Piezo buzzer (passive)	No oscillator; need AC/PWM signal	Any (you control it)	Drive with PWM from Arduino
Electromagnetic buzzer	Coil + metal diaphragm, 5V DC	Fixed ~2kHz	+ and −, polarity matters
Speaker (8Ω)	Voice coil in permanent magnet	20Hz – 20kHz	Needs amplifier circuit (LM386)

Connecting a buzzer with a transistor: Buzzer between VCC and transistor Collector. Transistor driven by a logic signal or Arduino pin (with 1kΩ base resistor). This allows a 3.3V microcontroller to drive a 12V buzzer safely — the transistor does the heavy lifting.

LESSON 4

DC Motor

A DC motor converts electrical energy into rotational mechanical energy using electromagnetic principles. When current flows through the armature coil inside a magnetic field, a force (Lorentz force) causes rotation. Reversing polarity reverses rotation direction.

DC MOTOR — ROTATING ARMATURE

⚙️ KEY DC MOTOR FACTS

Speed control: PWM (Pulse Width Modulation) — rapidly switching the motor ON and OFF at varying duty cycles. 50% duty = half speed. This is how an Arduino controls motor speed.
Direction control: Use an H-Bridge circuit (like the L298N chip) to reverse polarity electronically without rewiring. Essential for robots.
Back-EMF protection: When motor is switched OFF, the spinning armature generates a voltage that can damage transistors. Always place a flyback diode across the motor terminals.
Stall current: When a motor is held stationary and voltage applied, it draws maximum current (stall current) — far more than running current. Always rate your driver circuit for stall current.

LESSON 5

Relay — Electromagnetic Switch

A relay is an electrically operated mechanical switch. A small current through the electromagnet coil (control circuit) creates a magnetic field that pulls a metal armature, mechanically closing or opening a separate high-power contact (load circuit).

🔀 RELAY TYPES AND CONTACTS

Terminal	Meaning	Function
Coil + and −	Electromagnet input	Drive from transistor (5V/12V coil)
COM (Common)	Pivot contact	Always connected; moves when relay activates
NC (Normally Closed)	Closed at rest	Opens when relay energized — use for fail-safe
NO (Normally Open)	Open at rest	Closes when relay energized — use for switching on

Why use a relay? Your Arduino outputs 3.3–5V at very low current. A relay lets this tiny signal switch 230V AC household appliances safely — the control circuit and load circuit are COMPLETELY isolated. This is critical for mains-powered projects.

⚠️ Always use a flyback diode across the relay coil (cathode to +V, anode to the transistor side). When the coil is de-energized, it releases a large voltage spike that can destroy your transistor — the diode provides a safe path for this spike to dissipate.

LESSON 1

Using a Multimeter

A multimeter is the most essential tool in electronics. It measures Voltage (V), Current (mA/A), and Resistance (Ω) — and more. Every student must learn to use one correctly. Wrong settings can damage the meter or your circuit!

📏 HOW TO MEASURE EACH QUANTITY

Measurement	Dial Setting	How to Connect	Key Caution
Voltage (DC)	V DC (20V range)	Probes ACROSS the component (parallel). Red to +, Black to −.	Never connect in series — will short circuit!
Voltage (AC)	V AC (750V range)	Probes across component. Polarity doesn't matter for AC.	Respect 230V safety rules — never touch probes!
Current (DC)	mA or A range	BREAK the circuit, insert meter in series (circuit must flow through it).	Always start on highest range. Wrong connection = blown fuse!
Resistance	Ω (select range)	Remove component from circuit. Probes across component.	Never measure resistance in a powered circuit!
Continuity	Beep symbol (diode)	Probes across suspected break. Beep = connected.	Circuit must be OFF. Quick wire and fuse testing.
Diode test	Diode symbol	Red to Anode (+), Black to Cathode (−). Reads forward voltage.	Good diode: 0.4–0.7V. Damaged: 0V or OL.

⚠️ Most Common Mistake: Leaving the meter in current (mA) mode and trying to measure voltage. This creates a near-short circuit that immediately blows the meter's internal fuse! Always check dial position before connecting probes.

LESSON 2

Breadboard

A breadboard (prototype board) allows you to build and test circuits without soldering. Components and wires plug into the holes. Internal metal strips connect the holes in a specific pattern. Understanding this internal wiring is essential.

BREADBOARD INTERNAL CONNECTIONS

🧱 GOLDEN RULES FOR BREADBOARD USE

IC chips go across the center divider: Each pin sits in a separate row on each side of the divider, allowing you to connect individual pins without shorting them.
Power rails are for V+ and GND only: Connect your battery + to the red rail, − to the blue rail. Then use short jumpers to bring power to your component rows.
Always wire before powering: Build the complete circuit, then apply power. Diagnose any issues before adding voltage to avoid damage.
Color-code your wires: Use RED for positive/V+, BLACK for GND, and other colors for signal lines. This makes debugging dramatically easier.
Check component orientation: LEDs, capacitors, diodes, and transistors have polarity/pinout. Insert them in the correct orientation before powering up.

LESSON 3

Reading Schematics

A schematic (circuit diagram) is a standardized map of a circuit using universal symbols. Every electronic device has a schematic. Learning to read them is the most important skill in electronics — all datasheets, manuals, and project guides use them.

📄 STANDARD SCHEMATIC SYMBOLS

Symbol Description	Name	Notes
Long line + short line (repeated)	Battery/Voltage Source	Long = +, Short = −
Zigzag line (ANSI) or Rectangle (IEC)	Resistor	Arrow through = variable
Two parallel vertical lines	Capacitor (non-polar)	Curved plate = electrolytic (−)
Loops or bumps along a line	Inductor / Coil	Bars alongside = iron core (transformer)
Triangle pointing right with bar	Diode	Bar = Cathode (−). Arrow = Anode (+)
Triangle with light arrows	LED	Arrows point away from junction
Circle with B, C, E terminals	NPN Transistor	Arrow on Emitter points outward (NPN) or in (PNP)
Open line segment (angled)	Switch (open)	Line = closed switch
Horizontal lines decreasing in size	Ground (GND)	Three lines tapering downward
Crossed diagonal line over resistor symbol	Fuse	Or horizontal oval with zigzag inside

Reading Tips: Trace current flow from + terminal. Follow wires until you reach a component. Identify series vs parallel. Recognize common sub-circuits (voltage divider, transistor switch, RC filter). Labels like R1, C2, Q1 (transistor), U1 (IC) appear next to components with their values.

LESSON 4

PCB Basics

A PCB (Printed Circuit Board) is a flat board made of fiberglass (FR4) with copper "traces" that replace wires. Components are soldered onto the board. PCBs allow complex circuits to be miniaturized, mass-produced, and made reliable.

🟢 ANATOMY OF A PCB

Layer/Part	Material	Function
Substrate (base)	FR4 fiberglass	Structural foundation; non-conductive
Copper traces	35µm copper film	Replace wires; carry current between components
Solder mask	Green/blue/red epoxy	Insulates copper; prevents solder bridges; gives PCB its color
Silkscreen	White ink	Component labels, reference numbers, orientation marks
Pads/Footprints	Bare copper spots	Where components solder to the board
Vias	Copper-plated holes	Connect traces between layers in multi-layer PCBs

Designing your first PCB: Draw schematic in KiCad (free) → Assign footprints to components → Use PCB editor to place components and route copper traces → Export Gerber files → Submit to PCB manufacturer (JLCPCB, PCBWay — 5 boards for ~$2 shipping to Nepal).

Through-hole (THT) vs Surface-mount (SMD): THT components have long legs that go through holes and are soldered on the back. SMD components sit on pads on the surface — much smaller, harder to hand-solder, used in modern commercial electronics.
Soldering: Use a 60/40 lead-tin solder or lead-free SAC305. Iron tip at 350°C. Heat both pad and component leg, apply solder, let cool 2 seconds without moving. Good joint looks shiny and smooth. Cold joint looks dull/grainy.

PROJECT 1

Auto Night Light

Build a circuit that turns an LED ON automatically in darkness and turns it OFF in bright light — using an LDR, a transistor, and a few resistors. This is the fundamental principle behind streetlights, staircase lights, and solar garden lights.

PROJECT 01

🌙 LDR Auto Night Light

BEGINNER

Grade 7+

The LDR forms a voltage divider with R1. In the dark, R_LDR is very high — the voltage at the base of Q1 (BC547) is LOW, turning the transistor OFF and the LED OFF. When it's bright, R_LDR drops, the base voltage rises above 0.6V, transistor turns ON, and the LED glows. Adjusting R1 sets the light sensitivity threshold.

9V Battery

BC547 Transistor

LDR

10kΩ Resistor (R1)

470Ω Resistor (R2 — LED current limiter)

Red LED

Breadboard + Jumper Wires

🔧 STEP-BY-STEP BUILD

1

Insert BC547: Place the transistor across the center divider of your breadboard. Identify legs: flat face pointing toward you — left = Collector, middle = Base, right = Emitter.

2

LDR + R1 voltage divider: Connect one end of the LDR to the + power rail. Connect the other end of LDR to one end of R1 (10kΩ). Connect the other end of R1 to GND rail. The junction between LDR and R1 is your Base voltage point.

3

Wire the Base: Connect the LDR–R1 junction to the Base (B) pin of BC547 using a jumper wire.

4

LED with R2: Connect R2 (470Ω) from the + rail to the Anode (+) of your LED. Connect the LED Cathode (−, shorter leg) to the Collector (C) of BC547.

5

Emitter to GND: Connect the Emitter (E) of BC547 to the − (GND) rail.

6

Power up: Connect 9V battery — red wire to + rail, black to − rail. Cover the LDR with your hand — the LED should light up! Uncover it — LED should turn off.

💡 KEY CONCEPT: VOLTAGE DIVIDER AS SENSOR INPUT

The LDR and R1 form a voltage divider: V_base = 9V × R1 / (R_LDR + R1). In darkness, R_LDR ≈ 1MΩ, so V_base ≈ 0.09V — below the 0.6V threshold. In bright light, R_LDR ≈ 1kΩ, so V_base ≈ 8.2V — well above threshold, saturating the transistor. This divider principle is used in almost every analog sensor circuit.

PROJECT 2

Touch Alarm

Build a circuit that triggers a buzzer the moment you touch two exposed wires. Your body's resistance (~100kΩ) acts as a base resistor for a transistor, completing the circuit. Used in anti-tamper security, burglar alarms, and touch-activated displays.

PROJECT 02

👆 Human-Touch Alarm

BEGINNER

Grade 7+

When you bridge the two sensor wires with your fingertips, your skin resistance (~50kΩ–200kΩ) provides just enough base current to saturate the BC547 NPN transistor. The collector circuit drives a piezo buzzer. No touch = open base = transistor OFF = silence. Touch = transistor ON = alarm sounds.

9V Battery

BC547 NPN Transistor

Piezo Buzzer (active)

1MΩ Resistor (R1 — base pull-down)

Two bare copper wire probes

Breadboard + Jumpers

🔧 STEP-BY-STEP BUILD

1

Prepare sensor probes: Strip two 5cm pieces of wire. These are your touch sensor leads — they should be bare copper at the tips, spaced about 1cm apart on your board (or taped to a cardboard surface).

2

Place BC547: Insert across center divider. One probe wire connects to the + rail. The other probe wire connects to the Base of BC547 through a 1MΩ resistor (R1) which pulls the base to GND when not touched.

3

Connect the buzzer: Connect the + leg of the active piezo buzzer to the + rail. Connect the − leg to the Collector of BC547.

4

Emitter to GND: Wire Emitter directly to GND rail.

5

Test it: Power on. Touch both probe ends simultaneously with one finger — buzzer should sound immediately. Release — it stops. Try with wet vs dry fingers; notice how skin resistance changes the response.

💡 KEY CONCEPT: YOUR BODY AS A RESISTOR

Dry skin resistance is typically 100kΩ–10MΩ. Wet or sweaty skin drops to 1kΩ–10kΩ. With a BC547 needing only ~20µA base current to switch, even dry skin provides enough current at 9V: I = 9V ÷ 200kΩ = 45µA — sufficient. This is why touch sensors work reliably even through gloves if conductive enough. The 1MΩ pull-down ensures the base stays firmly at 0V when not touched, preventing false triggers from stray electric fields.

PROJECT 3

Water Level Indicator

Build a 3-level indicator that shows Empty, Half, and Full using three LEDs. Metal probes in a container detect when water (which conducts electricity) bridges a circuit. Used in overhead tanks, aquariums, and industrial fluid monitoring systems.

PROJECT 03

💧 3-Level Water Detector

INTERMEDIATE

Grade 8+

Three pairs of probes sit at different heights in a tank. When water rises to a probe pair, water's conductivity (~200–500µS/cm for tap water) closes the circuit, turning ON the corresponding BC547 transistor and lighting its LED. A common GND probe sits at the tank bottom. The three sense probes are at Low, Medium, and High positions.

9V Battery

3× BC547 Transistors (Q1, Q2, Q3)

3× LEDs (Red, Yellow, Green)

3× 470Ω Resistors (LED current limiters)

3× 10kΩ Resistors (base pull-downs)

4 metal/copper wire probes

Container of water + Breadboard

🔧 STEP-BY-STEP BUILD

1

Prepare probes: Cut 4 pieces of stiff copper wire (~10cm each). Strip insulation from both ends. These are your sensor probes — one is the common GND, three are level sensors at different heights.

2

Set probe heights: In a tall plastic cup or container: tape the GND probe to the bottom. Tape the LOW probe at 1/4 height, MID at 1/2, HIGH at 3/4 height. All probes should touch the water when at their respective levels.

3

Wire three identical transistor stages: For each stage — connect the sense probe through a 10kΩ pull-down to the Base of a BC547. Connect a 470Ω + LED (in series) from + rail to Collector. Emitter to GND. Wire GND probe to the circuit's GND rail.

4

Power and test: Connect 9V. With no water, all LEDs off. Add water to the LOW level — Red LED lights. Add more to MID — Yellow joins. Fill to HIGH — Green glows. All three lit means tank is full!

💡 KEY CONCEPT: WATER RESISTANCE & CONDUCTIVITY

Pure water is actually a poor conductor (~18MΩ·cm resistivity). Tap water conducts because it contains dissolved minerals (calcium, magnesium, chloride ions) with typical resistance of 1kΩ–50kΩ between probes 1cm apart. This is enough to drive a BC547 base when the pull-down resistor is ≥10kΩ. Saltwater conducts much better (~20Ω), while distilled water may not trigger the circuit at all — an important real-world variable to understand.

PROJECT 4

Temperature Alert

Build a circuit that triggers an alarm when temperature rises above a set threshold — using an NTC thermistor, a comparator voltage divider, and a buzzer. This is the core principle in fire alarms, refrigerator monitors, and engine overheat protection systems.

PROJECT 04

🌡️ Thermal Threshold Alarm

INTERMEDIATE

Grade 8+

An NTC thermistor (resistance decreases as temperature rises) forms a voltage divider with a fixed resistor R1. The output of this divider feeds the Base of a BC547 transistor. At normal temperature, the thermistor resistance is high → low base voltage → transistor OFF → buzzer silent. When it gets hot, thermistor resistance drops → base voltage rises → transistor turns ON → buzzer sounds. The threshold is tuned by adjusting R1 or using a potentiometer.

9V Battery

NTC Thermistor (10kΩ at 25°C)

BC547 NPN Transistor

10kΩ Potentiometer (threshold adjust)

Active Piezo Buzzer

470Ω Resistor (base protection)

Red LED + 470Ω (optional visual indicator)

Breadboard + Jumpers

🔧 STEP-BY-STEP BUILD

1

Wire the voltage divider: Connect one end of the NTC thermistor to + rail. Other end connects to one terminal of the 10kΩ potentiometer. The other pot terminal goes to GND. The wiper (middle pin) of the pot is your output voltage node.

2

Base connection: Connect the wiper (output node) through a 470Ω resistor to the Base of BC547. This 470Ω protects the transistor from excess base current.

3

Collector circuit: Connect the piezo buzzer between + rail and Collector. Optionally add a Red LED + 470Ω resistor in parallel with the buzzer for a visual alert.

4

Emitter to GND. Connect Emitter directly to GND rail.

5

Calibrate threshold: Power on at room temperature. Rotate potentiometer until buzzer is silent. Now hold the thermistor between your fingers — body heat (~37°C) should trigger it. Alternatively, briefly touch a warm cup. Adjust pot for desired sensitivity.

💡 KEY CONCEPT: NEGATIVE TEMPERATURE COEFFICIENT (NTC)

An NTC thermistor has resistance that drops exponentially with temperature, described by the Steinhart–Hart equation. A typical 10kΩ NTC thermistor at 25°C drops to ~3.5kΩ at 50°C and ~1.5kΩ at 70°C. Combined with a fixed 10kΩ R1: at 25°C, V_base = 9 × 10/(10+10) = 4.5V. This simple divider principle is used in virtually every appliance with a temperature sensor — washing machines, ovens, car engines, and air conditioners all use NTC thermistors with comparator circuits.

PROJECT 5

Wireless Power Transmission

Transmit power wirelessly using resonant inductive coupling — the same technology in your phone's wireless charger. A transmitter coil driven by an oscillator creates a changing magnetic field; a receiver coil picks up this energy and lights an LED, with no physical connection.

PROJECT 05

📡 Resonant Inductive Coupling

ADVANCED

Grade 9+

A simple transistor-based oscillator (Colpitts-like circuit) drives the TX coil at its resonant frequency. When the RX coil is tuned to the same frequency and brought within range, mutual inductance transfers energy across the air gap. A rectifier diode and smoothing capacitor on the RX side convert the AC induced voltage into DC to power an LED. Range is limited by coil size and coupling coefficient.

9V Battery

2N2222 or BC547 Transistor (oscillator)

TX Coil: 20 turns, 6cm diameter, 26AWG enameled wire

RX Coil: 20 turns, 6cm diameter, 26AWG enameled wire

1N4148 Diode (rectifier)

100µF Capacitor (smoothing)

2× 100nF Ceramic Capacitors (tank circuit)

10kΩ Resistor (base bias)

Red LED

MAGNETIC FIELD COUPLING BETWEEN COILS

🔧 STEP-BY-STEP BUILD

1

Wind both coils: Wrap 20 turns of 26AWG enameled copper wire around a 6cm circular former (a pill bottle or PVC pipe works well). Leave 10cm tails for connections. Scrape the enamel off both ends with sandpaper to expose bare copper. Wind RX coil identically.

2

Build the oscillator (TX side): Place BC547 on breadboard. Connect 10kΩ from + rail to Base. Connect one 100nF cap from Base to GND, another 100nF from Collector to the junction of the first cap (this forms the tank circuit). Connect TX coil between + rail and Collector.

3

Build the receiver (RX side): Connect the RX coil output to the Anode of 1N4148 diode. Cathode goes to one side of the 100µF capacitor (+ leg). Other cap leg to GND. Connect the LED (with no extra resistor needed — coil output is limited) across the capacitor.

4

Test and tune: Power the TX circuit. Bring the RX coil parallel to the TX coil, starting at 1cm distance. The LED should glow. Move it away slowly — note the maximum range. Tilt the coils — power drops dramatically when perpendicular (misaligned). This is why phone chargers require careful alignment!

💡 KEY CONCEPT: MUTUAL INDUCTANCE & RESONANCE

Mutual inductance M (measured in henries, H) describes how much of coil TX's changing magnetic flux links with coil RX. The induced EMF in RX = M × (dI/dt). Resonance occurs when the oscillator frequency equals 1 / (2π√LC) of the tank circuit — at resonance, even small M can transfer significant energy. Qi wireless charging (used in smartphones) extends this to 5–15W at up to 12mm, operating at 110–205 kHz. Larger systems (electric vehicle charging pads) use the same principle at up to 11kW.

PROJECT 6

Capstone Project

Design and build your own original circuit using everything you've learned across 8 months. This is an open-ended challenge — choose your problem, design your solution, build it, test it, and present it. This is exactly how real engineers work.

CAPSTONE

🏆 Your Original Design

OPEN-ENDED

All Grades

The capstone project is your chance to combine sensors, transistors, logic, and output devices to solve a real problem or build something you find fascinating. There are no required components — only required thinking. Below are suggested ideas at different levels of complexity, plus the engineering design process to follow.

🎯 SUGGESTED PROJECT IDEAS BY GRADE

Grade	Project Idea	Key Concepts Used
Grade 5–6	Battery-Powered Flashlight with ON/OFF switch + LED brightness control (POT)	Closed circuit, switch, LED, resistors, potentiometer
Grade 5–6	Simple Door Bell — push button triggers piezo buzzer	Switch, buzzer, series circuit, voltage divider
Grade 7–8	Soil Moisture Sensor — LEDs show dry / moist / wet using probe resistance	Voltage divider, comparator transistors, LEDs, sensors
Grade 7–8	Dark-Activated Desk Lamp with adjustable threshold	LDR, POT, transistor switch, relay, AC lamp (with teacher supervision)
Grade 9–10	Heartbeat Monitor — use IR LED + phototransistor to detect pulse in finger	Photodetectors, amplifier, LED display, timing circuits
Grade 9–10	Mini FM Transmitter — broadcast audio to nearby FM radio	LC oscillators, frequency tuning, antenna theory, audio coupling
Grade 9–10	Automatic Plant Watering — soil moisture → relay → water pump	Sensor → comparator → relay → actuator full chain

🔬 THE ENGINEERING DESIGN PROCESS

STEP 1 — DEFINE

State the problem clearly: "I want a circuit that does X when Y happens." Who uses it? What are the success conditions?

STEP 2 — RESEARCH

Which sensors detect your input? Which components control your output? Look up datasheets and similar projects to understand what's possible.

STEP 3 — DESIGN

Draw the schematic on paper first. Label all component values. Calculate resistor values using Ohm's law. Predict what happens at each node.

STEP 4 — PROTOTYPE

Build on breadboard. Test each sub-circuit independently before connecting them together. Use multimeter to verify voltages at each stage.

STEP 5 — TEST

Does it do what you said? Test all edge cases. What happens at minimum and maximum sensor values? What if power varies? Document failures honestly.

STEP 6 — ITERATE

Almost nothing works perfectly on the first try. Identify what failed, understand why, change one variable at a time, and test again. This is real engineering.

📋 CAPSTONE SUBMISSION CHECKLIST

Problem statement (1 paragraph): What does your circuit do? Who benefits from it? Why is it useful or interesting?
Schematic diagram: Hand-drawn or digital, with all component values labeled. Must use standard symbols learned in Month 7.
Component list with values: Every component used, its specification, and why you chose it (e.g., "470Ω to limit LED current to ~17mA at 9V").
Build photographs: Photo of the breadboard build from above, probes placed for measurement, and the circuit in operation.
Test results: What worked? What didn't? What did you change during troubleshooting? Include multimeter readings if applicable.
Reflection (3 sentences): What was the hardest part? What would you improve with more time or better components? What did you learn that surprised you?

🎓 WHAT YOU'VE LEARNED ACROSS 8 MONTHS

You started by asking "what is electricity?" — and you can now answer that at the level of electrons, fields, potential, and quantum conduction bands. You can calculate Ohm's Law, design series and parallel circuits, decode resistor color codes, explain how a capacitor stores charge, describe why a transistor amplifies current, read a schematic, debug a circuit with a multimeter, and build real projects that sense the physical world and respond to it. That is the foundation of every electronic device ever built. The next step — microcontrollers, programming, and embedded systems — is where everything comes together into the world of modern technology.