Learning Goals 5 min
Today we drill domains 1-4: electricity, schematics, components, IDE+boards. Sample questions with full explanations. By the end you will:
- Solve the typical "calculate the resistor" / Ohm's-law questions.
- Identify common schematic symbols at speed.
- Match components (capacitor, transistor, IC) to their roles.
- Pick the right board / IDE setting for a scenario.
Warm-Up 5 min
Pen + paper. Time yourself. Aim for < 2 minutes per question.
Sample Questions · Domains 1-4 60 min
Domain 1 · Electricity
A circuit has 9 V and 470 Ω. Current through the resistor?
Answer
I = V/R = 9 / 470 ≈ 19.1 mA. Rounded to common option: ~19 mA.
Two 220 Ω resistors in parallel. Equivalent resistance?
Answer
1/Req = 1/220 + 1/220 = 2/220. Req = 110 Ω.
A 5 V battery drives a 100 Ω resistor. Power dissipated?
Answer
P = V²/R = 25 / 100 = 0.25 W. A 1/8 W resistor would burn; need ≥ 1/4 W.
What does AC mean?
Answer
Alternating Current — current reverses direction periodically (e.g. household mains 50/60 Hz).
Domain 2 · Schematics & Datasheets
The symbol with two parallel lines, one shorter, represents:
- Resistor
- Capacitor
- Diode
- Battery
Answer
Battery (4). Long line = +, short line = −. Capacitor symbol has two equal-length lines (or curved one for polarised).
A diode symbol shows current flowing in which direction (when forward-biased)?
Answer
Anode (triangle) to Cathode (line). The triangle points in the direction current flows.
An NPN transistor's three pins are:
Answer
Base (control), Collector (top, current enters), Emitter (bottom, current exits). On the symbol the arrow points OUT of the emitter for NPN.
In a datasheet, "Absolute Maximum Ratings" means:
Answer
The values beyond which the chip will be damaged. Do NOT exceed. Different from "recommended operating conditions".
Domain 3 · Components
You want to read a button. Which is correct?
- Button between pin and GND,
pinMode(pin, INPUT); pressed = HIGH. - Button between pin and GND,
pinMode(pin, INPUT_PULLUP); pressed = LOW. - Button between pin and 5V,
pinMode(pin, INPUT_PULLUP); pressed = HIGH. - Button between pin and 5V,
pinMode(pin, INPUT); pressed = LOW.
Answer
2. INPUT_PULLUP holds the pin HIGH internally; the button pulls it LOW when pressed.
What does a flyback diode protect against?
Answer
The inductive voltage spike when a motor / relay / solenoid is switched off. Diode reverse-biased across the inductor catches the spike.
An LDR (light-dependent resistor):
- Generates current when light hits it.
- Decreases resistance in bright light.
- Increases resistance in bright light.
- Is unaffected by light.
Answer
2. Resistance drops with light intensity. Use in a voltage divider; analogRead gives brightness.
The function of a 100 nF capacitor next to a chip's VCC:
Answer
Decoupling — smooths supply noise at the chip's power pins, preventing brown-outs during sudden current spikes.
Domain 4 · IDE & Boards
The Arduino IDE's Boards Manager is for:
Answer
Installing support for additional board families (ESP8266, ESP32, Nano 33 BLE). Adds them to the Tools → Board menu.
A sketch shows "Region `data' overflowed". What does it mean?
Reveal
The static RAM usage exceeded the chip's capacity. Fix: move strings to flash with F(), reduce arrays, or upgrade to a board with more RAM.
The bootloader on an Arduino UNO is roughly:
- 2 KB of flash
- 0.5 KB of flash
- 32 KB of flash
- 1 KB of RAM
Answer
2. ~0.5 KB. Of the 32 KB total flash, ~31.5 KB is usable for sketches.
To upload via "Arduino as ISP", you connect:
Answer
Programmer's D10 → target RESET, D11 → MOSI, D12 → MISO, D13 → SCK, plus power + GND. ArduinoISP sketch on the programmer; Tools → Programmer = Arduino as ISP; Tools → Burn Bootloader.
Basic 15 min
Bench sprint · Domains 1 to 4
Questions like Q1–Q3 are easier once you have built them. A classmate made a press-to-light circuit. It works, but badly.
- LED (forward voltage 2 V): D9 → two 220 Ω resistors in parallel → LED → GND.
- Button: one leg to D2, the other leg to 5V. Nothing else on D2.
const int BUTTON_PIN = 2;
const int LED_PIN = 9;
void setup() {
pinMode(BUTTON_PIN, INPUT);
pinMode(LED_PIN, OUTPUT);
}
void loop() {
if (digitalRead(BUTTON_PIN) == HIGH) {
digitalWrite(LED_PIN, HIGH);
} else {
digitalWrite(LED_PIN, LOW);
}
}- Calculate the resistance of the two resistors in parallel, then the LED current. Is it safe?
- Replace them with one standard resistor for about 15 mA. Calculate the power in it. Is a ¼ W resistor enough?
- The LED sometimes flickers on when nobody touches the button. Explain the fault, then fix it in two different ways.
- Build your fixed circuit and measure the LED current with a multimeter.
It works if the LED stays off when the button is untouched, lights when pressed, and the meter reads about 13–14 mA.
Challenge 3 · Read a 9 V battery safely 10 min
This covers Domains 1, 2 and 4. A classmate wants to read a 9 V battery on A0. The UNO's pins must never see more than 5 V. They wired: battery + → 10 kΩ → A0 → 10 kΩ → battery −. The Serial Monitor shows 0.00 every time.
const int BATTERY_PIN = A0;
void setup() {
Serial.begin(9600);
}
void loop() {
int raw = analogRead(BATTERY_PIN);
float volts = raw * (5 / 1023);
Serial.println(volts);
delay(1000);
}- A fresh battery can read 9.6 V. Calculate the voltage at A0. Is it safe?
- Another classmate suggests 10 kΩ on top and 22 kΩ on the bottom. Calculate A0 for 9.6 V. Is that safe?
- Find the wiring fault: one connection is missing.
- Find the two code faults and fix them.
It works if the Serial Monitor reading is within 0.2 V of your multimeter reading across the battery.
Recap 5 min
Domains 1-4 = electricity, schematics, components, IDE. Quick mental maths (Ohm's law). Recognise symbols. Match components to roles. Tomorrow: domains 5-8.
- Voltage divider
- Two resistors splitting a voltage. Common for sensors that vary in resistance (LDR, thermistor, pot).
- Series / parallel
- R_series = R1 + R2. R_parallel = (R1 × R2) / (R1 + R2). Or for N equal: R_parallel = R / N.
- Forward bias
- The polarity where a diode conducts. Anode + to cathode −.
- Datasheet sections
- Absolute max, recommended operating, electrical characteristics, pinout, application notes. Read in that order.
- INPUT_PULLUP
- Pin mode that enables the AVR's internal pull-up resistor. Saves an external resistor for buttons.
- Bootloader
- Small program in flash that allows USB-based sketch upload. ~0.5 KB on UNO.
Extra Mission 5 min
Part 1 — Design a component tester
Domains 1 to 3 are about parts and how current flows through them. On paper, design a small tester that checks parts from your kit before you use them.
Your design must include:
- Which parts it tests (resistors, LEDs, buttons) and what it reports for each.
- The circuit it uses to measure, drawn as a schematic.
- How it keeps the current safe for the part and the pin.
- How it shows the result.
Part 2 — Make it
Build the resistor part of your tester. Put a known 10 kΩ resistor from 5V to A0, and the unknown resistor from A0 to GND. Read the voltage V at A0 and print R = 10,000 × V ÷ (5 − V). Test three resistors and check them against their colour bands.
Bring back next class: your uploaded sketch, a photo of the circuit and a Serial Monitor screenshot with all three readings and their colour-band values.