What each part does, the spec to check, and the one rule. Print me.
Resistor
Does Limits current; sets/divides voltage.
Check Value (Ω, color bands) + power rating (¼ W typical).
Polarity None — fits either way.
Rule: read bands with an app/meter; ¼ W is fine for signals.
Lesson 8 →
Ceramic capacitor
Does Decoupling / filtering — steadies the supply.
Check Value via 3-digit code (104 = 0.1 µF).
Polarity None.
Rule: 0.1 µF across power+GND beside every chip.
Lesson 9 →
Electrolytic capacitor
Does Bulk smoothing / energy storage.
Check Value + voltage rating (printed, e.g. 10µF 25V).
Polarity Yes! stripe = −, long leg = +.
Rule: never wire backwards — it can pop.
Lesson 9 →
Potentiometer
Does Adjustable voltage divider — a readable knob.
Check Resistance + taper (linear for sensing).
Wiring Outer pins = power/GND; middle = analog in.
Rule: read with analogRead (ESP32: 0–4095).
Lesson 10 →
Diode
Does One-way valve for current.
Check Type (rectifier / Schottky / Zener), current rating.
Polarity Band = cathode; current flows toward the band.
Rule: flyback across coils; series diode for reverse-polarity protection.
Lesson 11 →
LED
Does Emits light (a diode that glows).
Check Color/voltage; needs a series resistor.
Polarity Long leg = + (anode); flat side = − (cathode).
Rule: ~220–330 Ω in series on a 5V pin.
Lesson 1 →
Transistor (BJT / MOSFET)
Does Electrically-controlled switch for big loads.
Check Type, voltage/current rating, logic-level gate.
Wiring Pin → base/gate via ~1 kΩ; load on own supply.
Rule: MOSFET for hungry loads; add a flyback diode for coils.
Lesson 6 →
Integrated circuit (IC)
Does A whole circuit in a chip (regulator, sensor, MCU…).
Check Operating voltage; pinout; max ratings.
Orient Notch/dot = pin 1; count counter-clockwise.
Rule: power + GND + 0.1 µF cap; copy the datasheet's app circuit.
Lesson 12 →
Relay (module)
Does Isolated switch for big / mains loads.
Check Contact rating (e.g. 10A 250VAC) > your load.
Terminals COM / NO / NC; use COM→NO for off-by-default.
Rule: use a module; mains = power off, enclosure, ask first.
Lesson 7 →
DC motor
Does Spins continuously; polarity = direction.
Check Voltage & stall current (sizes the driver).
Drive Via a motor driver — never straight from a pin.
Rule: own supply, common ground; PWM = speed, 2 pins = direction.
Lesson 16 →
Motor driver (H-bridge)
Does Switches motor current; both directions + speed.
Check Voltage & current rating vs your motor.
Examples TB6612FNG, L298N.
Rule: both dir pins same = brake; includes flyback protection.
Lesson 16 →
Servo (hobby)
Does Moves to a commanded angle and holds.
Wiring 3 wires: power, ground, signal (to a GPIO).
Control Servo library: write(angle).
Rule: separate supply for all but tiny ones; share ground.
Lesson 17 →
Stepper motor
Does Precise, repeatable steps; holds position.
Check Steps/rev, voltage/current; needs a driver.
Examples A4988, 28BYJ-48 + ULN2003.
Rule: choose for precise multi-turn positioning; library sequences steps.
Lesson 17 →
Sensor (input)
Does Turns the world into a signal.
Digital on/off — PIR, reed → digitalRead.
Analog level — photoresistor, thermistor → divider.
Smart I²C/SPI — BME280 → library call.
Rule: check interface + voltage before wiring.
Lesson 18 →