Unit A - Foundations

01. Safety, Electricity & Breadboards

Work safely and build reliable low-voltage circuits.

Estimated time 2-3 hours

Learning outcomes

Explain voltage, current and resistance
Use Ohms law to choose an LED resistor
Recognise breadboard rails and connected rows
Use a multimeter without creating a short circuit

Parts and preparation

Arduino Uno, USB cable, breadboard, red LED, 220-330 ohm resistor, jumper wires and a digital multimeter.

Before power: inspect wiring, confirm supply voltage and ensure all connected circuits share GND.

Safety, Electricity & Breadboards instructional connection diagram — Open the diagram for a larger view. Trace every connection before building.

Electrical quantities

Voltage is electrical potential difference, measured in volts (V). Current is the flow of charge, measured in amperes (A). Resistance opposes current, measured in ohms. Ohms law is V = I R.

Choosing an LED resistor

For a 5 V output, a red LED drop of about 2 V and a target current of 10 mA: R = (5 - 2) / 0.010 = 300 ohm. A standard 330 ohm resistor is safe. Never connect an LED directly to an output pin.

Breadboard connections

The five holes in each terminal strip are normally connected. Long side rails distribute power, but some boards split these rails in the middle. Verify unfamiliar boards with continuity mode.

Safety rules

Use only extra-low-voltage DC circuits. Switch power off before rewiring. Never measure resistance on a powered circuit. When measuring current, place the meter in seriesnever directly across a supply.

Wiring and safe build sequence

Uno pin 8 -> 330 ohm resistor
Resistor -> LED anode (long leg)
LED cathode (flat side/short leg) -> GND

Power rule: switch off before moving wires. Arduino I/O pins are control signals; high-current loads require a driver and suitable external supply.

Worked sketch

Download .ino sketch

const int ledPin = 8;

void setup() 
{
  pinMode(ledPin, OUTPUT);
}

void loop() 
{
  digitalWrite(ledPin, HIGH);
  delay(500);
  digitalWrite(ledPin, LOW);
  delay(500);
}

How the code works

pinMode configures the electrical role of pin 8.
HIGH is approximately 5 V on an Uno; LOW is approximately 0 V.
The resistor limits LED and pin current.

Test and record evidence

Expected result: The LED flashes twice per second. Measure about 5 V from pin 8 to GND while it is on.

Practical evidence checklist

Labelled wiring or block diagram Uploaded sketch and observed result At least one measured/tested value Fault or improvement recorded in logbook

Common faults and checks

Reverse the LED if it never lights.
Confirm the resistor and LED share a connected breadboard row.
Check that the jumper returns to an Uno GND pin.

Extension challenge: Calculate a resistor for a 3.0 V blue LED at 8 mA from a 5 V output, then choose the next higher standard value.

Check your understanding

Q1. Why does an LED need a series resistor?

Show answer

To limit current through the LED and Arduino pin.

Q2. How are breadboard terminal rows connected?

Show answer

Usually in groups of five holes; power rails run lengthwise and may be split.