PROJECT 00 · FOUNDATIONS

Electronics & Communication Basics

Read this before anything else — the ideas every other project quietly assumes. No wiring yet.

Understand voltage, current, polarity, grounds, and how chips talk to each other, and the rest of the kit becomes easy (and you won't fry parts).

1 · Voltage, current, resistance

A helpful model is water in pipes:

Electrical	Unit	Water analogy
Voltage (V)	volt (V)	Pressure pushing the water
Current (I)	ampere (A)	Flow rate — how much moves
Resistance (R)	ohm (Ω)	Pipe narrowness — opposition to flow

Voltage is a difference between two points. "3.3 V" means 3.3 V relative to a reference — usually ground (GND, 0 V).
Current is charge flow; here it's small — milliamps (mA) (1000 mA = 1 A).
Resistance opposes current. Resistors are built to a specific value.

2 · Ohm's Law — the one equation to remember

V = I × R

Cover the one you want: V = I×R · I = V/R · R = V/I.

For a fixed voltage, more resistance → less current.

Why every LED gets a 220 Ω resistor

An LED barely resists current itself — straight across 3.3 V it draws too much and burns out. A series resistor limits the current. An LED drops ~2 V, leaving 1.3 V across the resistor:

I = V / R = (3.3 V − 2 V) / 220 Ω ≈ 0.006 A = 6 mA

6 mA is safe and bright — well under the ESP32's limits (§6). Power is P = V × I (watts); our circuits use tiny fractions of a watt, so parts stay cool.

3 · Polarity — and why direction matters

Polarity means a connection has a + (higher voltage) side and a − (lower / ground) side. Some parts only work one way around.

Conventional current flows + → through the parts → back to −. The LED only conducts one way.

Polarized part	+ side	− side
LED	anode (long leg)	cathode (short leg / flat notch)
Electrolytic capacitor	+ leg	− stripe
Diode	anode	cathode (band)
Modules / sensors	VCC / +	GND / −
Power (battery, USB)	+	−

Not polarized (either way): resistors, ceramic capacitors, pushbuttons.

Golden rule: before powering up, trace VCC → … → GND and confirm every polarized part faces the right way. A reversed LED just won't light; a reversed power connection to a module can destroy it.

4 · DC power, ground & short circuits

DC (Direct Current) flows one steady direction — batteries, USB, the ESP32. AC (wall outlets) reverses; we avoid it (except carefully via the relay in Project 7).
The board takes 5 V from USB and regulates it to the 3.3 V the chip uses. Headers: VIN ≈ 5 V, 3V3 = 3.3 V, GND = 0 V.
Ground is the shared 0 V reference. Every part connects to the same ground; two boards talking need a common ground.

Never create a short circuit. A wire from 3V3 straight to GND is near‑zero resistance → enormous current → overheating and damage. Never connect a power rail directly to ground.

5 · Digital signals & logic levels (3.3 V!)

Chips represent data as two voltage levels:

HIGH ≈ 3.3 V = logic 1
LOW ≈ 0 V = logic 0

The ESP32 is a 3.3 V device — putting 5 V on a GPIO can permanently damage it. When a module needs 5 V power (PIR, relay), power it from VIN but keep its signal wires at 3.3 V logic.

Analog is different: a continuous range 0–3.3 V that the ESP32's ADC reads as 0–4095 (Project 2).

6 · Current limits & good habits

≤ 40 mA per GPIO absolute; keep ≤ ~12 mA in practice → always use series resistors for LEDs.
Double‑check polarity before applying power.
Build with the board unplugged, then power up.
Keep a common ground across everything.
When unsure, measure with a multimeter (voltage between two points; continuity to check a connection).

7 · How chips talk to each other (buses)

Sensors, displays, and the ESP32 exchange bits over shared wires. Three standards cover almost everything in this kit — libraries handle the details, but knowing them helps you wire correctly.

UART · 2 wires · no clock

I²C · 2 shared wires · addresses

SPI · 4 wires · +CS each

UART — simplest (asynchronous serial)

2 wires, TX and RX, cross‑connected. No clock — both sides agree on a baud rate (why the Serial Monitor is always 115200). Point‑to‑point; the USB Serial Monitor uses UART via the CP2102 chip.

I²C — few wires, many devices

2 shared wires: SDA (data) + SCL (clock) — on the ESP32, GPIO 21 & 22. Each device has a unique address (the OLED is 0x3C), so many share the same pair. Needs pull‑ups (usually on‑module). The OLED (Project 10) uses I²C.

SPI — fast, more wires

4 wires: MOSI, MISO, SCK, plus a CS per device. Full‑duplex and fast — displays, SD cards, high‑rate sensors. ESP32 VSPI: MOSI 23, MISO 19, SCK 18, CS 5.

	Wires	Clock?	# devices	Speed	In this kit
UART	2 (TX, RX)	No (baud)	1‑to‑1	Low–med	USB Serial Monitor
I²C	2 (SDA, SCL)	Yes	Many (addresses)	Low–med	OLED (Project 10)
SPI	4 (+CS each)	Yes	Many (CS each)	High	displays / SD cards

8 · Further reading (beginner‑friendly)

Want a deeper explanation of any idea above? These free, well‑illustrated guides are excellent starting points.

Fundamentals

Tools

Communication buses

ESP32‑specific

ESP32 pinout reference (Random Nerd Tutorials)
Our own GPIO Reference and Components Glossary.

External links open on third‑party sites and were chosen for being clear and beginner‑friendly.

9 · You're ready

With these fundamentals you can reason about every circuit in the kit. Next: