Activity 1.1.2 — Investigating Basic Circuits¶

Learning Objectives¶

By the end of this lesson, students will be able to:

Identify basic electronic components: resistors, LEDs, and capacitors
Explain the structure and purpose of a breadboard (protoboard)
Use a Digital Multimeter (DMM) to measure voltage, current, and resistance
Interpret common circuit diagram symbols
Define voltage, current, and resistance and explain their relationships

Vocabulary¶

Vocabulary (click to expand)

Term	Definition
Voltage (V)	The electrical force that pushes charge through a circuit; measured in volts
Current (I)	The flow of electrical charge through a conductor; measured in amperes (amps)
Resistance (R)	The opposition to the flow of current; measured in ohms (Omega)
Circuit	A complete path through which electricity can flow
Open circuit	A break in the circuit; no current flows
Short circuit	An unintended path with very low resistance; dangerous
Multimeter	An instrument that measures voltage, current, and resistance
Breadboard	A reusable platform for building temporary circuits without soldering
LED	Light Emitting Diode; a component that emits light when current flows through it

Part 1: Basic Electronic Components¶

Resistors¶

Resistors are components that resist the flow of current. They are used to:

Limit current to protect sensitive components
Divide voltages
Set bias conditions in circuits

Key specifications: - Resistance value — Measured in ohms (Omega) - Power rating — How much power (watts) the resistor can safely dissipate - Tolerance — How close the actual value is to the marked value

Resistors are covered in detail in Lesson 1.1.4.

LEDs (Light Emitting Diodes)¶

LEDs are special diodes that emit light when current flows through them. Unlike traditional bulbs, LEDs are:

More energy efficient
Longer lasting
Available in many colors
Polarized (they have positive and negative leads)

LED Symbols and Identification:

Standard LED symbol:
    |--|-->|--
     |     |
    anode  cathode

    (arrow = light emission)

Identifying LED leads: - The longer lead is typically the anode (+) - The flat edge on the LED housing indicates the cathode (-)

Caution: LEDs can be damaged by too much current. Always use a current-limiting resistor in series with an LED.

Capacitors¶

Capacitors store electrical energy in an electric field. They are used for:

Filtering (smoothing power supply fluctuations)
Timing circuits
Energy storage
Coupling signals between circuit stages

Types of capacitors: - Ceramic — Small, non-polarized, good for high frequencies - Electrolytic — Larger, polarized, higher capacitance - Tantalum — Polarized, stable, used in critical applications

Important: Electrolytic capacitors can explode if connected with reverse polarity!

Part 2: Breadboard Basics (Protoboard)¶

A breadboard (also called protoboard) is a reusable platform for building and testing circuits without soldering. This allows you to quickly change and test circuit designs.

How Breadboards Work¶

Inside a breadboard are metal strips that connect rows of holes. Components pushed into the same row are electrically connected.

Breadboard cross-section:

    Top view:        Row numbers
    +---+---+---+     1  2  3  4  5
    | o | o | o |     a  b  c  d  e  <- terminal strip
    | o | o | o |     f  g  h  i  j
    | o | o | o |

    Internal metal strips:

    +-------+-------+-------+  <- Connected holes (same row)
    |       |       |       |

    GAP (no connection across center)

    |       |       |       |
    +-------+-------+-------+  <- Another connected section

Key Rules¶

Rows are connected — holes in the same row are electrically common
Columns are NOT connected — holes in the same column are isolated (unless wired)
Power rails are connected vertically — entire columns along the edge
The center gap — rows 1-20a/e are separated from 21-25a/e (for ICs)
Power rails run the full length — red/blue rails on the sides

Breadboard vs. PCB¶

Feature	Breadboard	PCB (Printed Circuit Board)
Construction	Temporary, no solder	Permanent, soldered
Speed	Fast prototyping	Slower to fabricate
Changes	Easy to modify	Difficult to change
Reliability	Wires can come loose	Fixed connections
Parasitic effects	More capacitance/inductance	Controlled
Use case	Testing/learning	Final products

Part 3: Using a Digital Multimeter (DMM)¶

A DMM is your most important diagnostic tool. Learn to use it properly.

Measurement Modes¶

Mode	Symbol	Measures	Connection
DC Voltage	V with straight line	Battery, power supplies	Red to positive, black to common
AC Voltage	V with wavy line	Wall outlets, AC circuits	Red to hot, black to neutral/ground
DC Current	A with straight line	Current flowing through circuit	Break circuit, insert meter
Resistance	Omega symbol	Resistance of component	Component must be isolated
Continuity	Diode/beep symbol	Tests if circuit is complete	Beeps when < 30 ohms

How to Measure¶

Measuring Voltage (parallel connection):

    +v
    |
   [R1]
    |
    +--------+--------+
    |                 |
    |        V        |
    |       meter     |
    |                 |
    +--------+--------+

Measuring Current (series connection):

    +v                    +v
    |                     |
   [R1]                  [R1]
    |                     |
    +----------+          |
               |          |
              [A]        +----------+
             meter      |          |
               |         |         |
    -----------+         +---------+

Measuring Resistance: - Remove the component from the circuit (or at least disconnect one end) - Touch probes to component leads - Read the value

Key insight: Always measure voltage in parallel, current in series, and resistance with the component isolated. Connecting a meter wrong can damage the meter or the circuit.

Part 4: Circuit Diagram Symbols¶

Circuit diagrams (schematics) use standardized symbols to represent components.

Common Symbols¶

Component	Symbol	Notes
DC Voltage Source	+
AC Voltage Source	circle with ~	Wave inside for AC
Ground	three horizontal lines (decreasing)	Reference point
Resistor	zigzag or rectangle	Either style accepted
LED	triangle with arrows	Arrow shows light emission
Capacitor	two parallel lines	One line curved for polarized
Switch (SPST)	break in line with lever	Shows open/closed state
Wire junction	dot where lines cross	Connected
No connection	line crossing without dot	NOT connected

Part 5: Voltage, Current, and Resistance¶

These three concepts form the foundation of all circuit analysis.

Voltage (V) — Electrical Pressure¶

Voltage is the "pressure" that pushes charge through a circuit. Think of it like water pressure in pipes.

Symbol: V
Unit: Volts (V)
Named after: Alessandro Volta (inventor of the battery)
Analogy: Water pressure pushing water through pipes

Examples: - AA battery: 1.5V - USB power: 5V - Car battery: 12V - Wall outlet: 120V (AC)

Current (I) — Flow of Charge¶

Current is the actual flow of electrons through a conductor.

Symbol: I (or sometimes A for current)
Unit: Amperes, or amps (A)
Named after: Andre-Marie Ampere
Analogy: Gallons of water flowing per minute

Important: Current is the same through all parts of a series circuit.

Resistance (R) — Opposition to Flow¶

Resistance is how much a material opposes the flow of current.

Symbol: R
Unit: Ohms (Omega)
Named after: Georg Ohm
Analogy: Narrow pipe restricting water flow

All conductors have some resistance. Even wires have small resistance.

Part 6: The Water Analogy¶

Understanding V, I, and R is easier with the water analogy:

WATER SYSTEM                    ELECTRICAL SYSTEM
+--------+                      +--------+
| High   |   Pressure = V       | High   |
| Tank   |--------------------->| Terminal| (V)
|        |   Flow rate = I      |        |   Current = I
+--------+                      +--------+
    |                                |
   [Pipe                         [Resistor
   narrow]                         (R)]
    |                                |
+--------+                      +--------+
| Low    |   Low pressure       | Low    |
| Tank   |--------------------->| Terminal| (GND)
+--------+                      +--------+

Relationships: - More pressure (V) = more flow (I) - Narrower pipe (high R) = less flow (I) - Wider pipe (low R) = more flow (I)

Summary¶

Concept	Symbol	Unit	Analogy
Voltage	V	Volts (V)	Water pressure
Current	I	Amps (A)	Flow rate
Resistance	R	Ohms (Omega)	Pipe width

Resistors limit current and protect components
LEDs emit light when current flows, are polarized
Capacitors store energy; electrolytics can be dangerous if reversed
Breadboards allow temporary circuit construction without soldering
Multimeters measure voltage, current, and resistance
V, I, and R are related — change one affects the others

Quick Check¶

When measuring voltage, do you connect the meter in series or parallel?

Parallel. Voltage is measured across a component, so the meter goes in parallel with it.

What happens if you connect an electrolytic capacitor with reverse polarity?

It can explode or vent violently — electrolytic capacitors are polarized and must be connected with the correct + and - orientation.

How is a breadboard's center gap designed to be used?

The center gap is sized for ICs (integrated circuits) to straddle — each pin connects to one side of the gap.

Key Reminders¶

Never connect a meter in the wrong mode — it can damage the meter or circuit
Measure voltage with meter in parallel; measure current in series
LEDs are polarized — connect them the right way around
The center gap on a breadboard is for ICs to straddle
Electrolytic capacitors can explode if connected with reverse polarity
Always disconnect power before measuring resistance
Current flows through a complete circuit; no complete path = no current

Custom activity — adapted from PLTW Digital Electronics