Reference · Living document

Glossary

The shared vocabulary for the whole course. Terms are added as we meet them.

Core electrical quantities

Voltage (volts, V)

The "push" or pressure that drives electric charge. It is always measured between two points (a difference). In the water analogy: water pressure. Sometimes called potential difference.

Current (amps, A · often milliamps, mA)

The flow of electric charge — how much is moving past a point per second. In the water analogy: the rate of water flow. 1000 mA = 1 A.

Resistance (ohms, Ω)

How much a material opposes the flow of current. In the water analogy: a narrow or constricted pipe. Higher resistance → less current for the same voltage.

Ohm's Law

The relationship between the three above: V = I × R. In plain words — more pressure pushes more flow; more resistance allows less flow. You rarely need the algebra; you need the intuition.

Power (watts, W)

The rate at which energy is used or delivered. P = V × I. What makes things get hot, bright, or move. Added in a later lesson.

Circuit fundamentals

Circuit

A complete loop that current can flow around, from a source's positive terminal, through components, and back to its negative terminal. Break the loop and current stops.

Closed vs. open circuit

Closed = the loop is complete, current flows. Open = the loop is broken (e.g. a switch off), no current flows.

Short circuit

An accidental low-resistance path that lets current bypass the intended load. Causes a large, often dangerous current. The thing rules of thumb exist to prevent.

Ground (GND)

The common reference point of a circuit — the "0 V" against which voltages are measured, and the return path for current. On an Arduino, the GND pins.

Series vs. parallel

Series: components in a single-file line, same current through each. Parallel: components side by side across the same two points, same voltage across each. Detailed in a later lesson.

Building blocks & gear

Breadboard

A reusable board for building circuits with no soldering. Internal metal strips connect certain holes together (rows and power rails).

Microcontroller

A tiny computer on a chip that runs your code and controls pins. The Arduino and ESP32 are boards built around one. The ESP32 also has built-in WiFi.

Resistor

A component that adds a fixed resistance — used to limit current (e.g. protecting an LED) or set voltages. Value read from color bands or printed digits.

Relay

An electrically-controlled switch. Lets a small, safe signal (from your microcontroller) switch a much larger load (like a household lamp). Central to home automation — and to be treated with respect when mains power is involved.

Transistor

An electrically-controlled switch (or valve): a small current/voltage at the base controls a much larger current between the other two terminals. Lets a weak pin drive a strong load. BJT (e.g. 2N2222) for small loads; MOSFET (logic-level type) for hungry loads like motors and LED strips.

Capacitor

Stores a small amount of charge; used to smooth supply voltage and "decouple" noise. Think of a tiny rechargeable buffer that steadies the flow.

Diode

A one-way valve for current — flows one direction, blocks the other. An LED is a diode that emits light. A flyback diode is one placed across a coil/motor to absorb the voltage spike when it switches off (protects the transistor).

Schematics & reading circuits

Schematic

A diagram of what's connected to what — a map, not a picture. Lines are wires; symbols are parts with letter labels (R, C, D, Q, U, SW). See the symbol cheat-sheet.

Node (net)

A set of points all joined by wire — electrically the same point. Everything on one node is at the same voltage.

Microcontroller & signals

Logic level

The voltage a board treats as HIGH or LOW. Common values: 3.3V (ESP32) and 5V (Arduino Uno). Mixing them on signal lines needs a logic level converter to avoid damage.

Floating

An input pin connected to neither HIGH nor LOW — it drifts and reads random noise. Fixed with a pull resistor.

Pull-up / pull-down resistor

A resistor (~10 kΩ) that weakly ties a pin to + (pull-up) or GND (pull-down), giving it a definite default state. Many boards have built-in pull-ups (INPUT_PULLUP).

Debounce

Smoothing out the brief mechanical "bounce" of a button so one press registers once, not several. Done in code or with a small capacitor.

Switching & isolation

Relay module

A ready-made board carrying a relay plus its driver transistor, flyback diode, and often an optocoupler — so you can switch it straight from a microcontroller pin. The beginner-safe way to use a relay.

Isolation

A deliberate lack of electrical connection between two parts of a circuit (e.g. the low-voltage control side and the mains side of a relay). The barrier that makes safe control of dangerous loads possible.

Optocoupler

A part that passes a signal across an isolation barrier using light instead of a wire — adds safety between control and load sides.

COM / NO / NC

A relay's switch terminals. COM = common pole; NO (normally open) is disconnected until the relay activates; NC (normally closed) is connected until it activates. Wire loads through COM→NO so they default to off.

Components in depth

Voltage divider

Two resistors in series; the point between them sits at a smaller voltage, set by the resistor ratio. Used to scale a voltage down and to read resistive sensors. See Lesson 8.

Power rating

How much heat a part (e.g. a resistor) can dissipate before failing — typically ⅛–1 W for hobby resistors. ¼ W is fine for signal-level work.

Farad (F)

The unit of capacitance. Real parts are tiny fractions: microfarads (µF), nanofarads (nF), picofarads (pF). A ceramic marked 104 = 0.1 µF.

Decoupling (bypass) capacitor

A small cap (usually 0.1 µF) across a chip's power and ground, placed close to it, that supplies sudden current bursts and steadies the supply. Add one to every IC.

Wiper

The movable middle contact of a potentiometer — the pin that outputs the variable voltage.

Potentiometer ("pot")

A three-terminal variable resistor / adjustable voltage divider. Outer pins to power and ground, wiper (middle) to an analog input. Read with analogRead().

Anode / cathode

A diode's two ends. Current flows from the anode (flat side of the triangle) toward the cathode (the bar; marked with a band on real parts).

Schottky / Zener diode

Schottky: low forward drop (~0.3 V), fast — good for protection/efficiency. Zener: conducts backwards at a set voltage — used as a simple voltage reference/limiter.

Integrated circuit (IC)

An entire circuit built into one chip (a regulator, sensor, motor driver, or microcontroller). Needs power, ground, and a decoupling cap. See Lesson 12.

DIP (dual in-line package)

The common breadboard-friendly IC body: two rows of pins 0.1" apart that straddle the center gap. A notch or dot marks pin 1.

Datasheet

The manufacturer's spec document for a part. Hunt it for four things: pinout, operating voltage/current, absolute maximum ratings, and the typical application circuit.

VCC / VDD / GND / VSS

Power-pin labels on chips. VCC/VDD = positive supply; GND/VSS = ground (0 V).

Microcontroller, signals & buses

GPIO

General-Purpose Input/Output — a programmable pin you can set as a digital input or output, often with extra functions (analog, PWM, bus). See Lesson 13.

Peripheral

Built-in hardware inside a microcontroller that handles a job for you — ADC, PWM/timers, and the I²C/SPI/UART bus controllers.

ADC (analog-to-digital converter)

The peripheral that measures a pin's voltage and returns a number (analogRead): 0–1023 on an Uno, 0–4095 on an ESP32.

PWM (pulse-width modulation)

"Fake analog" output: switch a pin on/off rapidly and vary the on-fraction. Used for dimming, motor speed, and servo signals. Set with analogWrite (0–255). See Lesson 14.

Duty cycle

The fraction of each PWM cycle the signal is HIGH. Higher duty cycle → higher average → brighter/faster.

Bus (I²C / SPI / UART)

A shared set of wires for exchanging data with modules. I²C: 2 shared wires (SDA/SCL), many addressed devices — the hobby default. SPI: 4 wires, fast, one CS per device. UART: 2 wires (TX/RX), point-to-point, also the PC link. See Lesson 15.

Motion & the physical world

DC motor

Spins when given voltage; polarity sets direction, voltage sets speed. An inductive load — needs a driver and its own supply. See Lesson 16.

Motor driver / H-bridge

A board that switches a motor's current under low-power control. The H-bridge inside can reverse polarity (both directions) and includes flyback protection. Speed via PWM, direction via two pins.

Servo

A geared motor + control electronics in one box that moves to a commanded angle. Three wires (power, ground, signal); driven by a PWM-style pulse via the Servo library. See Lesson 17.

Stepper motor

Rotates in precise, counted steps and holds position without feedback. Needs a driver. Best for repeatable, precise positioning.

Sensor

An input device that turns a physical quantity into a signal — read as digital (on/off), analog (a level via a divider), or over a bus (a "smart" I²C/SPI module). See Lesson 18.

Connectivity

Station mode / Access Point mode

Station (STA): the ESP32 joins an existing Wi-Fi network (use this for home automation). Access Point (AP): the ESP32 becomes its own hotspot, handy for first-time setup. See Lesson 19.

IP address

A device's address on a network (e.g. 192.168.1.42), assigned by the router. How other devices reach your gadget on the local network.

HTTP / web server

The web's request/response protocol. A client (browser) requests; a server (your ESP32) responds with a page or value. URLs can act as commands (/on, /off). See Lesson 20.

MQTT

A lightweight publish/subscribe messaging protocol for IoT. Devices publish/subscribe to topics via a central broker; senders and receivers are decoupled. The smart-home default. See Lesson 21.

Broker / Topic (MQTT)

The broker is the central server that routes messages. A topic is a named channel (e.g. home/livingroom/temperature) that publishers send to and subscribers listen on.

Publish / subscribe

The MQTT pattern: publish a message to a topic; subscribe to receive messages on a topic. Event-driven and many-to-many, unlike HTTP's request/response.

Home Assistant (HA)

Free, local, open-source home-automation hub: dashboards, device entities, and automations. Connect an ESP32 via ESPHome or MQTT. See Lesson 22.

ESPHome

A system for describing an ESP32/ESP8266 gadget in a short YAML config; it builds the firmware and integrates natively with Home Assistant (auto-discovery, over-the-air updates). The easy on-ramp.

MQTT Discovery

A convention where a device announces itself on the broker so Home Assistant auto-creates the matching entities — no manual per-device setup.

Analog audio & guitar effects

AC signal / waveform

A voltage that swings above and below a center over time (alternating current). A guitar pickup produces one; its size is loudness and its shape is tone. Effects reshape it. See Lesson 23.

Bias / Vref / virtual ground

A reference voltage at about half the supply (~4.5 V on 9 V), made with two equal resistors + a cap, so an AC signal can swing both ways on a single-supply circuit. See Lesson 24.

Coupling capacitor

A capacitor in the signal path that passes AC and blocks DC — lets the audio move between stages while each keeps its own bias. (Contrast decoupling cap, which steadies power.)

Impedance / input impedance

A signal's "resistance to being drawn from." A guitar is high-impedance and easily loaded down (tone suck); a high input impedance (~1 MΩ) or a buffer preserves the tone.

Gain

How many times bigger the output is than the input. Unity (1) = a buffer; greater than 1 = a boost. Set by two resistors around an op-amp. See Lesson 25.

Op-amp (operational amplifier)

An IC that amplifies the difference between its two inputs; with a couple of resistors it becomes a predictable amplifier — the workhorse of most pedals.

Clipping

Flattening a waveform's peaks when it's too big to fit. Adds harmonics = distortion. Soft (diodes in the op-amp feedback loop) → overdrive; hard (diodes to ground) → distortion. See Lesson 26.

Overdrive / distortion / fuzz

Degrees of clipping: gentle (overdrive), heavy (distortion), extreme transistor clipping (fuzz). Diode material (germanium ~0.3 V, silicon ~0.7 V, LED ~1.7 V+) flavors the sound.

Filter (low-pass / high-pass) & cutoff

A resistor + capacitor that passes some frequencies and weakens others, with the changeover at a cutoff frequency set by the values. Low-pass = tone (cut highs); high-pass = tighten bass. Bigger cap → lower cutoff. See Lesson 27.

LFO (low-frequency oscillator)

A slow wave (well below hearing) that continuously modulates part of a circuit — volume (tremolo), delay time (chorus/vibrato), or a filter (phaser).

BBD / PT2399

Delay chips. BBD (bucket-brigade): classic analog delay. PT2399: cheap, through-hole digital delay chip (~30–340 ms) that's the DIY favorite. See Lesson 28.

Bench skills & debugging

Multimeter

The core measuring tool. Four functions: DC voltage (across two points, powered on), continuity (beep test for connections, powered off), resistance, and diode test. See Lesson 30.

Continuity

A test (the beep setting) for whether two points are electrically connected (near 0 Ω). Done with power off — great for finding broken connections and shorts.

Signal tracing / half-split

Following a signal through a circuit to find where it disappears. The half-split method checks the midpoint to halve the search each time. See Lesson 32.

Audio probe

A DIY tool — a 0.1 µF cap on a wire to your amp, plus a ground clip — that lets you hear the signal at any point in a circuit, to localize a fault.

Ground loop

When ground is connected by two different paths, forming a loop that picks up hum like an antenna. Avoided by star-grounding to one common point. See Lesson 33.

Isolated power supply

A supply whose outputs don't share a ground path, preventing ground loops between powered devices (vs a cheap daisy-chain). The quiet way to power multiple pedals.

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