Level 3 Recap & Cert Vocab

Learning Goals 5 min

One lesson to consolidate 47 lessons. We'll quiz the protocols, glance back at the eight clusters, and lock in the certification vocabulary you'll see on the L4 exam-prep lessons. By the end of this lesson you will:

1. Recall the headline idea of each of L3's 8 clusters (A–H) plus the 3 builds (I).
2. Distinguish the four communication protocols you met — UART, I²C, SPI, Bluetooth Classic vs BLE — by pin count, speed, and use case.
3. Self-grade against a 12-question protocol-heavy quiz, identifying any clusters that need another look before Level 4.

Warm-Up 10 min

Open all your L3 sketches and your engineering notebook. Today is the last L3 lesson — flick through, remember what you built.

The 8 clusters at a glance

Recap · The four protocols 20 min

Choose by question: How many devices? UART = 1, I²C = many, SPI = few. Distance? Wires = within a board, Bluetooth = ~10 m, WiFi = a building, internet = anywhere.

One-line cluster recaps

• A · Servos: 3-wire pulse-position, Servo library, slew-limiting.
• B · DC motors: H-bridge + flyback diode + signed PWM speed.
• C · Steppers: count clicks for absolute position, Stepper library, 28BYJ-48 + ULN2003.
• D · Protocols: UART point-to-point, I²C shared bus, SPI 4-wire fast.
• E · Bluetooth: Classic for Android, BLE for everything.
• F · WiFi: ESP boards, HTTP client AND server, JSON APIs.
• G · Time + Glue: NTP gives time, webhooks push to the world.
• H · OOP: arrays → structs → classes, write once, reuse forever.
• I · Builds: scale up earlier projects with the new tools.

Quiz · Twelve protocol-heavy questions 25 min

Write your answers in your notebook before revealing. Each question maps to one or two lessons; if you get it wrong, that's the lesson to revisit.

Basic 10 min

Five lines from across Level 3. Each one is wrong. Write the corrected line and say what the wrong one would do.

1. Talking to an SSD1306 at address 0x3C: Wire.beginTransmission(0x78);
2. Opening an HC-05 in AT mode: bt.begin(9600);
3. Turning a 28BYJ-48 (2048 steps per turn) by 60°: stepper.step(60);
4. A phone must be able to change this value: BLEByteCharacteristic ledChar("19B10001-E8F2-537E-4F6C-D104768A1214", BLERead);
5. An ESP web server's whole loop(): delay(1000);

It works if each fix matches the lesson it came from. Missed one? The quiz above names the lesson to revisit.

Challenge 3 · Four broken builds 10 min

Each build below worked in class and then failed at home. Predict the fault and give the fix.

• (a) WiFi lamp. The page opens on a laptop at http://192.168.1.42. A phone on mobile data cannot open it at all.
• (b) Bluetooth car. The phone pairs, but F does nothing and no OK comes back. The sketch has SoftwareSerial bt(2, 3);. HC-05 TXD goes to D3, and RXD (through the divider) goes to D2.
• (c) Plant monitor. A dry plant sends 40 alerts in one hour. The sketch has only two states: OK and MAYBE_DRY.
• (d) Pan-tilt mount. Both SG90s now take power from the UNO's 5V pin. The UNO resets whenever both servos move together.

It works if each fix is one change — a wire, a line of code or a power source — and names the lesson it comes from.

Final recap 5 min

You finished Level 3. You can drive any combination of motor, talk to any sensor on any of three protocols, put a device on the internet, push notifications from physical events to phones, write reusable class-based code, and reason about power budgets. Level 4 is the cert prep — same hardware skills, sharper exam-style focus, plus IoT cloud, MQTT, edge AI, robotics, and a full mock exam in the last lesson. See you in L04-01.

Pulse-position modulation (servos)

1.0–2.0 ms pulse every 20 ms encodes angle.

H-bridge

Four-transistor circuit for bidirectional DC motor control.

Stepper

Motor that advances in fixed angular "clicks" — count steps for position.

UART / I²C / SPI

Three serial protocols: point-to-point, multi-drop, four-wire-fast.

Address byte (I²C)

7-bit device ID + R/W bit. First byte of every transaction.

Chip select (SPI)

Per-peripheral wire that selects who's being talked to.

Bluetooth Classic vs BLE

Classic = UART-over-air (Android); BLE = attribute-based (iOS + Android).

HTTP client / server

Fetch vs serve. Same protocol, opposite directions.

JSON

The lingua franca of web APIs. Use ArduinoJson to parse/build.

Webhook

Outbound POST that triggers something on a remote service.

NTP

Network Time Protocol — real-world clock for any internet device.

Class

Struct + methods + access control. Encapsulation building block.

Constructor / begin()

Setup pair: constructor before setup(), begin() inside it.

Power budget

Capacity ÷ average draw = runtime. Account for peak sag separately.

Brownout

Supply sag below regulator minimum → chip reset.

Bulk capacitor

Big cap across noisy load's power rails to smooth peaks.

Pull-up resistor

Hold a wire HIGH when nothing's driving. Required on I²C lines.

Flyback diode

Protects switches from inductive kicks when motors / coils turn off.

Extra Mission 5 min

Part 1 — Design your own Level 3 capstone

You now know motors, protocols, Bluetooth, WiFi, webhooks, time and classes. Design one project that joins at least three of these clusters. Ideas: a Bluetooth car that sends a Discord message when it finds a wall, a WiFi pan-tilt camera stand with a daily sweep, a plant monitor with a servo flag that waves when the soil is dry.

Your design must include:

• The project's name and its one job.
• The three or more clusters it uses, and what each one does in it.
• A wiring table with every pin.
• At least one class or struct, with its fields and methods.
• A power budget and your battery or supply choice.

Part 2 — Make it

Build the core of your capstone: the two most important parts working together. Use only parts and ideas from Levels 1–3. Keep loop() free of long delay() calls.

Bring back to L04-01: your design, your uploaded sketch, and a short video of the core working.