Module 1: Electricity Fundamentals — Before You Plug Anything In

Level: 🟢 Beginner
Board: None (theory + multimeter + components)
Prerequisites: None
Estimated time: 2–3 hours
Goal: Build a working mental model of electricity and learn to stay safe.

What You'll Learn

By the end of this module, you'll understand what voltage, current, and resistance actually are — not just as formulas, but as intuition you'll use every time you build a circuit. You'll calculate resistor values, read component markings, use a multimeter, and build your first LED circuit entirely from first principles.

No Arduino yet. That comes in Module 2. Here, we focus on the physics, because every debugging session you'll ever have comes down to "is the right voltage in the right place?"

1.1 The Three Fundamentals: Voltage, Current, and Resistance

Voltage (V) — The Push

Voltage is electrical pressure. It's the difference in electric potential between two points that makes current want to flow. A 9V battery has 9 volts of "push" between its positive and negative terminals.

Key intuition: voltage is always measured between two points. When someone says "this pin is at 5V," they mean 5V relative to ground (0V).

Common voltages you'll encounter:

• 1.5V — single AA/AAA battery
• 3.3V — many microcontrollers and sensors
• 5V — Arduino Uno pins, USB power
• 9V — 9V battery, common for motor circuits
• 12V — LED strips, some motors and relays

Current (I) — The Flow

Current is the actual flow of electrons through a conductor, measured in amperes (A). In our projects, we usually deal with milliamps (mA) — thousandths of an amp.

Key intuition: current is what does the work. An LED lights up because current flows through it. A motor spins because current flows through its coils. Too much current and things overheat or burn out.

Typical currents in Arduino projects:

• 1–20 mA — LEDs
• 10–40 mA — per Arduino output pin (absolute max 40 mA)
• 50–500 mA — small motors, servos
• 500 mA–1 A — Arduino Uno total board consumption limit

Resistance (R) — The Friction

Resistance opposes the flow of current, measured in ohms (Ω). Every component has some resistance. Resistors are components specifically designed to provide a precise, controlled amount of resistance.

Key intuition: resistance is how we control current. Without a resistor in front of an LED, too much current flows and the LED burns out. Resistance is your primary tool for protecting components.

1.2 Ohm's Law — The One Formula You'll Actually Use

V = I × R

This is the relationship between voltage, current, and resistance. If you know any two, you can find the third:

• V = I × R → Voltage equals current times resistance
• I = V / R → Current equals voltage divided by resistance
• R = V / I → Resistance equals voltage divided by current

Worked Example: Choosing a Resistor for an LED

You have a 5V power source and a red LED. The LED datasheet says:

• Forward voltage (Vf): 2.0V
• Recommended forward current (If): 20 mA

Step 1: Calculate the voltage the resistor must drop.

V_resistor = V_source - V_LED = 5V - 2V = 3V

Step 2: Use Ohm's Law to find resistance.

R = V / I = 3V / 0.020A = 150Ω

Step 3: Pick a standard resistor value. 150Ω exists as a standard value. If it didn't, you'd round up to the next standard value (e.g., 220Ω) — using more resistance than needed is safe; using less is not.

Rule of thumb: When in doubt, round up. A dimmer LED is better than a dead one.

Practice Problems

Try these yourself before checking the answers:

1. You have a 9V battery and a green LED (Vf = 2.2V, If = 20 mA). What resistor do you need?
2. You measure 3.3V across a 1kΩ resistor. How much current is flowing?
3. A sensor draws 15 mA from a 5V supply. What's its effective resistance?

1.3 Power — Why Components Have Ratings

P = V × I

Power, measured in watts (W), tells you how much energy a component is converting per second — usually into heat. Every component has a maximum power rating. Exceed it and the component overheats.

Worked Example: Resistor Power Rating

Using our LED example above: the resistor drops 3V with 20 mA flowing through it.

P = V × I = 3V × 0.020A = 0.06W = 60 mW

A standard 1/4W (250 mW) resistor handles this easily. But if you were dropping 12V across a resistor with 100 mA:

P = 12V × 0.100A = 1.2W

A 1/4W resistor would literally catch fire. You'd need at least a 2W resistor.

Safety rule: Always check whether your resistor's power rating can handle the actual power dissipation. This is the calculation beginners most often skip — and the most common cause of burning smells.

1.4 Series vs. Parallel Circuits

Series: One Path

Components in series share one path for current. The same current flows through every component. Voltages add up.

In series:

• Current is the same everywhere: I_total = I₁ = I₂ = I₃
• Voltages add: V_total = V₁ + V₂ + V₃
• Resistances add: R_total = R₁ + R₂ + R₃

Example: Two 100Ω resistors in series = 200Ω total.

Parallel: Multiple Paths

Components in parallel share the same two connection points. The same voltage appears across each. Currents add up.

In parallel:

• Voltage is the same across all: V_total = V₁ = V₂ = V₃
• Currents add: I_total = I₁ + I₂ + I₃
• Resistances: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃

Example: Two 100Ω resistors in parallel = 50Ω total.

Why This Matters

When you wire two LEDs in series off a 5V supply, each gets less voltage. When you wire them in parallel, each gets the full voltage but the power supply must provide more current. Understanding this is essential for multi-LED projects, sensor arrays, and motor circuits.

1.5 Reading Resistor Color Codes

Resistors use colored bands to indicate their value. A 4-band resistor reads as:

Color-to-Number Table

Example Reading

A resistor with bands: Brown – Black – Brown – Gold

• Brown = 1, Black = 0, Brown = ×10, Gold = ±5%
• Value: 10 × 10 = 100Ω ±5%

Practice

What value are these resistors?

1. Red – Red – Brown – Gold
2. Orange – Orange – Red – Silver
3. Brown – Black – Orange – Gold

Practical tip: When in doubt, use your multimeter. Color bands on small resistors can be hard to read under certain lighting, and a 2-second measurement is faster than squinting.

1.6 Capacitor Markings

Capacitors store small amounts of electrical charge. You'll encounter two main types:

Electrolytic Capacitors (cylindrical, have a polarity stripe)

• Marked directly: "100µF 25V" means 100 microfarads, rated up to 25V
• Polarity matters! The stripe with minus signs indicates the negative leg. Reversing polarity on electrolytic capacitors can cause them to fail, sometimes violently.

Ceramic Capacitors (small discs or rectangles, no polarity)

• Use a 3-digit code: first two digits are the value, third is the number of zeros, result in picofarads (pF)
• Example: "104" = 10 × 10,000 = 100,000 pF = 100 nF = 0.1 µF

Capacitance Units

1.7 Component Identification

Here are the components you'll encounter in this course. Learn to recognize them now — it saves time later.

Resistor

• Looks like: Small cylinder with colored bands and two wire leads
• Does: Limits current. Protects other components.
• No polarity — can be inserted either way

LED (Light Emitting Diode)

• Looks like: Small colored or clear dome with two legs of different lengths
• Does: Emits light when current flows through it in the correct direction
• Has polarity: Longer leg = anode (+), shorter leg = cathode (−). A flat edge on the dome also marks the cathode.
• Needs a current-limiting resistor — always

Diode

• Looks like: Small cylinder with a single colored band on one end
• Does: Allows current to flow in one direction only. The band marks the cathode (−).
• Has polarity — the band indicates which side is cathode

Capacitor (Electrolytic)

• Looks like: Small cylinder, often with a stripe marking the negative side
• Does: Stores charge. Used for power smoothing and filtering.
• Has polarity — pay attention to the stripe

Capacitor (Ceramic)

• Looks like: Small flat disc or rectangle, often orange or blue
• Does: Same as electrolytic but smaller values. Used for noise filtering.
• No polarity — can be inserted either way

Transistor

• Looks like: Small black component with three legs (often has a flat side)
• Does: Acts as an electronic switch or amplifier. Lets a small current control a large one.
• Pin order matters — always check the datasheet for base, collector, emitter

Pushbutton / Tactile Switch

• Looks like: Small square button, usually with four legs
• Does: Connects a circuit when pressed, disconnects when released
• No polarity — but note that the four legs are internally connected in pairs

Potentiometer

• Looks like: Round knob with three pins
• Does: Variable resistor. Turning the knob changes resistance between the middle pin and the outer pins.
• Three pins: Two outer pins are the ends of the resistor; the middle pin is the wiper

Photoresistor (LDR — Light Dependent Resistor)

• Looks like: Small disc with a squiggly pattern on top, two legs
• Does: Resistance changes based on light level. More light = lower resistance.
• No polarity — can be inserted either way

1.8 Your First Tool: The Multimeter

A multimeter is the single most important tool you'll own for electronics. It measures voltage, current, resistance, and continuity.

Essential Functions

Measuring Voltage (DC V):

1. Set the dial to DC voltage (V with a straight line, not the wavy one)
2. Select a range higher than your expected voltage (or use auto-range)
3. Touch the red probe to the point you want to measure, black probe to ground
4. Read the display

Measuring Resistance (Ω):

1. Disconnect the component from any circuit — measuring resistance in-circuit gives false readings
2. Set the dial to Ω
3. Touch the probes to each end of the component
4. Read the display

Continuity Test (🔊):

1. Set the dial to continuity (beep symbol)
2. Touch the probes to two points
3. If there's a connection (very low resistance), the meter beeps
4. Use this to verify wires are connected, check solder joints, or find shorts

Measuring Current (A):

1. Set the dial to DC current (A with a straight line)
2. Move the red probe to the current jack (usually labeled "mA" or "A")
3. Break the circuit and insert the meter in series — current must flow through the meter
4. Read the display
5. Move the probe back to the voltage jack when done — leaving it in the current jack and accidentally measuring voltage can blow the meter's fuse

Common beginner mistake: Trying to measure current by touching the probes across a component (like you do for voltage). This creates a short circuit through the meter. Always connect the meter in series for current measurement.

1.9 Electrical Safety

This course uses low-voltage DC only (up to 12V). At these voltages, the risk of electrical shock to you is essentially zero. But you can still damage components, start small fires, and make expensive mistakes.

Safety Rules for This Course

1. Never connect mains voltage (120V/240V) to anything in this course. Mains electricity can kill. Mains work requires professional training and certification.
2. Double-check polarity before powering on. Reversing power connections can destroy components instantly.
3. Never exceed component ratings. Voltage ratings, current ratings, and power ratings all exist for a reason.
4. Disconnect power before rewiring. Making changes to a live circuit is how you create accidental short circuits.
5. Short circuits generate heat. If you smell burning or a wire gets hot, disconnect power immediately.
6. Electrolytic capacitors can hold charge. Even after disconnecting power, large capacitors may still have voltage. Discharge them before handling.
7. Lithium batteries require extra care. They can deliver enormous current if shorted and may catch fire or explode. Use protected cells and proper charging circuits only.

1.10 Reading Datasheets — Starting Early

Every electronic component has a datasheet — a document from the manufacturer that tells you everything about how the component works and what its limits are.

You don't need to read the entire thing (they can be dozens of pages). Here's what to look for first:

Key Datasheet Sections

Practice: Reading an LED Datasheet

For a typical 5mm red LED, you'll find:

• Forward voltage (Vf): 1.8–2.2V (use 2.0V for calculations)
• Forward current (If): 20 mA typical, 30 mA absolute max
• Reverse voltage: 5V max (applying more than this backwards will destroy it)
• Viewing angle: 20–30° for focused, 100–120° for diffused

From Module 6 onward, reading datasheets is mandatory. Start getting comfortable with them now.

Module Project: Your First LED Circuit — By Hand Calculation

Objective

Build a simple LED circuit on a breadboard. But instead of copying a diagram, you'll determine the correct resistor value yourself using what you've learned.

Components Needed

Steps

Step 1: Check your LED's datasheet (or use typical values)

Typical 5mm red LED:

• Forward voltage (Vf): 2.0V
• Forward current (If): 20 mA

Step 2: Calculate the resistor value

V_supply = 6V (4 × AA batteries)
V_resistor = V_supply - V_LED = 6V - 2.0V = 4.0V
R = V_resistor / I_LED = 4.0V / 0.020A = 200Ω

Nearest standard value: 220Ω (round up for safety).

Step 3: Verify the power dissipation

P_resistor = V_resistor × I_LED = 4.0V × 0.020A = 0.08W = 80 mW

A standard 1/4W (250 mW) resistor is more than adequate.

Step 4: Wire it up

1. Insert the LED into the breadboard. The longer leg (anode, +) goes into one row, the shorter leg (cathode, −) goes into an adjacent row.
2. Connect the 220Ω resistor from the LED's anode row to a new row.
3. Connect a jumper wire from the resistor's other end to the battery holder's positive (+) wire.
4. Connect a jumper wire from the LED's cathode row to the battery holder's negative (−) wire.
5. Insert batteries.

The LED should light up.

Step 5: Verify with your multimeter

• Measure the voltage across the LED. It should read approximately 1.8–2.1V.
• Measure the voltage across the resistor. It should read approximately 3.9–4.2V.
• Confirm: V_LED + V_resistor ≈ V_battery (these should roughly add up to your supply voltage).
• Optional: Measure the current by placing your meter in series. It should read approximately 18–20 mA.

Circuit Diagram

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 600 300" font-family="monospace" font-size="12">
  <!-- Battery -->
  <rect x="50" y="100" width="60" height="100" fill="none" stroke="#333" stroke-width="2" rx="4"/>
  <text x="80" y="90" text-anchor="middle" font-size="14" font-weight="bold">6V</text>
  <text x="80" y="120" text-anchor="middle" font-size="10">4×AA</text>
  <line x1="65" y1="140" x2="95" y2="140" stroke="#333" stroke-width="3"/>
  <line x1="70" y1="155" x2="90" y2="155" stroke="#333" stroke-width="2"/>
  <text x="100" y="143" font-size="10">+</text>
  <text x="100" y="158" font-size="10">−</text>

  <!-- Positive wire to resistor -->
  <line x1="110" y1="140" x2="200" y2="140" stroke="red" stroke-width="2"/>

  <!-- Resistor -->
  <rect x="200" y="130" width="80" height="20" fill="none" stroke="#333" stroke-width="2" rx="3"/>
  <text x="240" y="145" text-anchor="middle" font-size="11">220Ω</text>
  <text x="240" y="170" text-anchor="middle" font-size="10" fill="#666">¼W</text>

  <!-- Wire from resistor to LED -->
  <line x1="280" y1="140" x2="370" y2="140" stroke="red" stroke-width="2"/>

  <!-- LED -->
  <polygon points="370,120 370,160 410,140" fill="none" stroke="red" stroke-width="2"/>
  <line x1="410" y1="120" x2="410" y2="160" stroke="red" stroke-width="2"/>
  <text x="390" y="110" text-anchor="middle" font-size="11" fill="red">LED</text>
  <!-- Light rays -->
  <line x1="400" y1="118" x2="408" y2="105" stroke="red" stroke-width="1" stroke-dasharray="2,2"/>
  <line x1="410" y1="115" x2="418" y2="102" stroke="red" stroke-width="1" stroke-dasharray="2,2"/>

  <!-- Negative wire back to battery -->
  <line x1="410" y1="140" x2="480" y2="140" stroke="blue" stroke-width="2"/>
  <line x1="480" y1="140" x2="480" y2="220" stroke="blue" stroke-width="2"/>
  <line x1="480" y1="220" x2="80" y2="220" stroke="blue" stroke-width="2"/>
  <line x1="80" y1="220" x2="80" y2="200" stroke="blue" stroke-width="2"/>
  <line x1="80" y1="200" x2="110" y2="155" stroke="blue" stroke-width="2"/>

  <!-- Current direction arrow -->
  <text x="300" y="135" text-anchor="middle" font-size="10" fill="#666">→ I = 20mA →</text>

  <!-- Voltage labels -->
  <text x="240" y="195" text-anchor="middle" font-size="10" fill="#0066cc">V = 4.0V</text>
  <text x="390" y="185" text-anchor="middle" font-size="10" fill="red">V = 2.0V</text>
</svg>

Circuit Schema (JSON)

{
  "module": 1,
  "project": "First LED Circuit",
  "schematic": {
    "components": [
      {
        "id": "BAT1",
        "type": "battery_pack",
        "value": "6V",
        "description": "4×AA battery holder",
        "pins": {
          "positive": "net_vcc",
          "negative": "net_gnd"
        }
      },
      {
        "id": "R1",
        "type": "resistor",
        "value": "220",
        "unit": "ohm",
        "power_rating": "0.25W",
        "color_code": ["red", "red", "brown", "gold"],
        "pins": {
          "pin1": "net_vcc",
          "pin2": "net_r1_led"
        }
      },
      {
        "id": "LED1",
        "type": "led",
        "color": "red",
        "forward_voltage": 2.0,
        "forward_current_ma": 20,
        "pins": {
          "anode": "net_r1_led",
          "cathode": "net_gnd"
        }
      }
    ],
    "nets": [
      {
        "name": "net_vcc",
        "description": "Positive supply rail (6V)",
        "nodes": ["BAT1.positive", "R1.pin1"]
      },
      {
        "name": "net_r1_led",
        "description": "Connection between resistor and LED anode",
        "nodes": ["R1.pin2", "LED1.anode"]
      },
      {
        "name": "net_gnd",
        "description": "Ground rail (0V)",
        "nodes": ["BAT1.negative", "LED1.cathode"]
      }
    ],
    "power": {
      "supply_voltage": 6.0,
      "supply_type": "battery",
      "total_current_ma": 20
    }
  },
  "breadboard": {
    "connections": [
      {
        "step": 1,
        "instruction": "Insert LED: anode (long leg) into row 15 column E, cathode (short leg) into row 15 column F",
        "component": "LED1"
      },
      {
        "step": 2,
        "instruction": "Insert 220Ω resistor: one leg into row 15 column A (same row as LED anode), other leg into row 10 column A",
        "component": "R1"
      },
      {
        "step": 3,
        "instruction": "Jumper wire from row 10 column B to positive (+) power rail",
        "type": "wire",
        "color": "red"
      },
      {
        "step": 4,
        "instruction": "Jumper wire from row 15 column J (same row as LED cathode) to negative (−) power rail",
        "type": "wire",
        "color": "black"
      },
      {
        "step": 5,
        "instruction": "Connect battery holder: red wire to positive rail, black wire to negative rail",
        "component": "BAT1"
      }
    ]
  },
  "validation": {
    "expected_measurements": {
      "voltage_across_led": { "min": 1.8, "max": 2.2, "unit": "V" },
      "voltage_across_resistor": { "min": 3.8, "max": 4.2, "unit": "V" },
      "current_through_circuit": { "min": 17, "max": 22, "unit": "mA" }
    },
    "common_mistakes": [
      "LED inserted backwards (no light, no damage at this voltage)",
      "Resistor and LED in same breadboard row but not actually connected via internal rails",
      "Battery holder wires reversed",
      "Using the wrong resistor value (check color bands with multimeter)"
    ]
  }
}

Self-Check: Module 1

Before moving to Module 2, make sure you can:

• Explain what voltage, current, and resistance are in your own words
• Use Ohm's Law to calculate any missing value given the other two
• Calculate power dissipation and verify a resistor can handle it
• Determine total resistance for series and parallel combinations
• Read a 4-band resistor color code
• Decode a 3-digit capacitor marking
• Identify the components listed in this module by sight
• Use a multimeter to measure voltage, resistance, and continuity
• Build the LED circuit project and verify your calculations with measurements

Key Terms Glossary

Next: Module 2 — Meet the Arduino: Your First Programmed Circuit →