Activity 1.2.7 — Unit 1 Review & Assessment

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Learning Objectives

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

1. Demonstrate mastery of all Unit 1 concepts
2. Apply problem-solving strategies to unfamiliar circuit scenarios
3. Complete the Unit 1 Assessment successfully
4. Identify areas needing additional study before proceeding to Unit 2

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Vocabulary

Vocabulary (click to expand)

Term	Definition
Engineering Design Process	A structured approach to solving problems through research, design, testing, and documentation
Ohm's Law	V = I × R; relationship between voltage, current, and resistance
Kirchhoff's Voltage Law (KVL)	The sum of voltage drops around a closed loop equals the source voltage
Kirchhoff's Current Law (KCL)	The sum of currents entering a junction equals the sum leaving
Binary	A number system using only 0 and 1
Analog-to-Digital Converter (ADC)	A circuit that converts continuous analog signals to discrete digital values
555 Timer	An IC that generates timing signals and clock pulses

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Part 1: Safety Review

General Lab Safety Rules

Rule	Description	Why It Matters
Goggles ON	Always wear safety glasses in the lab	Protects eyes from flying components, solder, and debris
Power OFF	Turn off power before building/modifying	Prevents shock and component damage
Check Before Power	Verify connections before applying power	Catches mistakes before they cause problems
No Food/Drink	Keep food and beverages away from workspace	Prevents contamination and spills
Know Location	Know where fire extinguisher and first aid kit are located	Enables quick response to emergencies

Electrical Hazards

Hazard	Danger	Prevention
Shock	Current through body can cause burns, cardiac arrest	Keep hands away from live circuits, use proper insulation
Short Circuit	Excessive current can cause burns and fire	Check for accidental connections before powering
Static Discharge	ESD can destroy sensitive components	Use wrist straps and ESD-safe mats
Overheating	Components can get hot enough to burn	Allow ventilation, turn off if smoking
Arc Flash	High voltage can create dangerous arcs	Never work on high-voltage circuits

Fire Extinguisher Types

Type	Color	Use For	DO NOT Use On
Class A	Green	Ordinary combustibles (wood, paper, trash)	Electrical fires
Class B	Red	Flammable liquids (gasoline, oil, paint)	Electrical fires
Class C	Blue	Electrical equipment	Combustibles
Class D	Yellow	Combustible metals (magnesium, titanium)	Other fire types
ABC	Multi	Most common - works on A, B, and C	Check if expired

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Part 2: Component Review

Analog Components

Component	Symbol	Function	Key Values
Resistor	[ZZZ]	Limits current, divides voltage	100Ω - 1MΩ, ¼W - 2W
Capacitor	[		]
Inductor	[)))	Stores energy in magnetic field	µH to mH range
Diode	[▶	]	Allows current in one direction
LED	[▶	◀◀]	Light-emitting diode

Resistor Color Code

Color Code Reference:
  0 = Black      5 = Green     Tolerance:
  1 = Brown      6 = Blue        Gold = ±5%
  2 = Red        7 = Violet     Silver = ±10%
  3 = Orange     8 = Gray       None = ±20%
  4 = Yellow     9 = White

Example - Resistor with bands: Brown, Black, Orange, Gold
  Digit 1 = 1
  Digit 2 = 0
  Multiplier = 1,000
  Value = 10 × 1,000 = 10,000Ω = 10kΩ ±5%

Digital Components

Component	Function	Example ICs
Logic Gates	Basic Boolean operations	74LS00, 74LS08, 74LS32
Flip-Flops	Store 1 bit of data	74LS74, 74LS76
Counters	Count clock pulses	74LS90, 74LS93
Decoders	Convert binary to display	74LS47, 74LS48
Timers	Generate clock signals	NE555
Registers	Store multiple bits	74LS173, 74LS374

Component Package Styles

Package	Description	Use Case
Through-Hole (TH)	Pins go through PCB holes	Breadboarding, prototyping
Surface Mount (SMD)	Pins on package surface	Mass production, small devices
DIP	Dual In-line Package	ICs with two parallel rows
SOIC	Small Outline IC	Compact SMD applications
QFP	Quad Flat Package	Microcontrollers, processors

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Part 3: Circuit Analysis Review

Ohm's Law Triangle

        ┌─────────────┐
        │      V      │
        │   (Voltage) │
        └──────┬──────┘
               │
       ┌───────┴───────┐
       │               │
       ▼               ▼
  ┌─────────┐    ┌─────────┐
  │    I    │    │    R    │
  │ (Current)│    │(Resistance)
  └─────────┘    └─────────┘

  V = I × R      I = V ÷ R      R = V ÷ I

Practice Problem — Ohm's Law

A 12V source is connected to a 470Ω resistor. What current flows through the circuit?

Show Solution

Given:
  V = 12V
  R = 470Ω

Formula:
  I = V ÷ R
  I = 12V ÷ 470Ω
  I = 0.0255A = 25.5mA

The current through the resistor is approximately 25.5 mA.

Series vs Parallel Circuits

Series Circuit: - Same current through all components - Voltages add up across components - Total resistance = R1 + R2 + R3 + ...

Parallel Circuit: - Same voltage across all components - Currents add up through branches - 1/Rtotal = 1/R1 + 1/R2 + 1/R3 + ...

Kirchhoff's Laws

KVL (Voltage Law):

Vsource = V1 + V2 + V3 + V4
12V     = 4V  + 3V  + 2V  + 3V
12V     = 12V ✓

KCL (Current Law):

Iin = Iout
I1  = I2 + I3 + I4
10mA = 3mA + 4mA + 3mA
10mA = 10mA ✓

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Part 4: Scientific and Engineering Notation

SI Prefixes

Prefix	Symbol	Multiplier	Example
Tera	T	10^12	2.5 TB hard drive
Giga	G	10^9	4 GB RAM
Mega	M	10^6	100 MHz clock
Kilo	k	10^3	4.7 kΩ resistor
(none)	-	10^0	5V supply
milli	m	10^-3	25 mA current
micro	µ	10^-6	100 µF capacitor
nano	n	10^-9	10 ns propagation delay
pico	p	10^-12	22 pF bypass capacitor

Engineering Notation Rules

1. Use prefixes that give 1-3 digits before prefix
2. Values should be between 1 and 999 before the prefix
3. Prefix must be one of the standard SI prefixes

Correct:     4,700Ω = 4.7kΩ
Correct:     0.0047A = 4.7mA
Incorrect:   4700Ω = 4700Ω (not standard form)
Incorrect:   0.0047A = 4700µA (technically correct but unusual)

Practice Problem — Engineering Notation

Convert 0.000000056 Farads to engineering notation.

Show Solution

Starting value: 0.000000056 F

Count decimal places: 6 places (0.000001 = 1µ)
0.000000056 = 56 × 10^-9

56 × 10^-9 = 56 nF

For engineering notation, we need 1-3 digits before prefix:
56 nF is within range (1-999) ✓

Answer: 56 nF or 5.6 × 10^-8 F

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Part 5: Binary and Number Systems

Decimal to Binary Conversion

Decimal	Binary	Method
0	0000	-
1	0001	1
2	0010	2
3	0011	2 + 1
4	0100	4
5	0101	4 + 1
6	0110	4 + 2
7	0111	4 + 2 + 1
8	1000	8
9	1001	8 + 1
10	1010	8 + 2
11	1011	8 + 2 + 1
12	1100	8 + 4
13	1101	8 + 4 + 1
14	1110	8 + 4 + 2
15	1111	8 + 4 + 2 + 1

Binary to Decimal Method

Example: Convert 1101₂ to decimal

Position:    1     1     0     1
Weight:      2³    2²    2¹    2⁰
             8     4     2     1

Calculation: (1×8) + (1×4) + (0×2) + (1×1)
           = 8 + 4 + 0 + 1
           = 13

1101₂ = 13₁₀

Practice Problem — Binary Conversion

Convert decimal 42 to binary.

Show Solution

Method: Subtract largest powers of 2

42 - 32 = 10    → 1 × 32
10 - 8  = 2     → 1 × 8
2  - 2  = 0     → 1 × 2
0  - 1  = (no)  → 0 × 1

Binary from MSB to LSB:
32  16   8   4   2   1
 1   0   1   0   1   0

42₁₀ = 101010₂

Verification:
(1×32) + (0×16) + (1×8) + (0×4) + (1×2) + (0×1)
= 32 + 0 + 8 + 0 + 2 + 0
= 42 ✓

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Part 6: Analog vs Digital Signals

Signal Comparison

Characteristic	Analog	Digital
Values	Continuous range	Discrete states (0, 1)
Noise immunity	Low (distortion adds)	High (thresholds)
Precision	Unlimited resolution	Limited by bit count
Bandwidth	Continuous	Sampled (Nyquist)
Processing	Amplify, filter	Logic operations
Storage	Difficult	Easy (memory)

Analog-to-Digital Conversion

┌─────────────────────────────────────────────────────────────────┐
│                    ADC PROCESS                                   │
├─────────────────────────────────────────────────────────────────┤
│                                                                 │
│  Analog Input                    Digital Output                  │
│  (continuous)                  (discrete samples)              │
│                                                                 │
│     │                          1001                             │
│ 5V ─┼─\                        0111                             │
│     │   \    ┌─────────┐       0101                             │
│ 3V ─┼────\──▶│   ADC   │───▶  0100                             │
│     │       │         │       0011                             │
│ 1V ─┼───────\─────────┘       0010                             │
│     │                         0001                              │
│ 0V ─┼──────────────────────── 0000                             │
│     └─────────────────────────────────▶ Time                    │
│       │  │  │  │  │  │  │  │                                  │
│       ▼  ▼  ▼  ▼  ▼  ▼  ▼  ▼  (Sample points)                 │
│                                                                 │
└─────────────────────────────────────────────────────────────────┘

Key ADC Parameters:
- Resolution: Number of bits (8-bit = 256 levels)
- Sample Rate: Samples per second (44.1 kHz = CD quality)
- Nyquist: Sample rate must be 2× highest frequency

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Part 7: 555 Timer and Clock Signals

555 Astable Mode Summary

Parameter	Formula	Example (R=10kΩ, C=10µF)
High Time	0.693 × R × C	0.0693s
Low Time	0.693 × R × C	0.0693s
Period	0.693 × R × C × 2	0.1386s
Frequency	1.443 ÷ (R × C)	7.2 Hz
Duty Cycle	High ÷ Period × 100%	50%

Clock Signal Parameters

Clock Signal Characteristics:

      High
  ────────────────┐
                  │         ┌───────────────┐
                  │         │               │
  ────────────────┘         │               │
      Low                   │               │
                    │       │               │
                    └───────┘               │
                          │                 │
                    │     │                 │
                    ├─────┼─────────────────┤
                          ↑
                    Rising edge

Frequency (f): Number of cycles per second (Hz)
Period (T): Time for one complete cycle (seconds)
Duty Cycle: Percentage of time signal is HIGH
Rise Time: Time to transition from LOW to HIGH
Fall Time: Time to transition from HIGH to LOW

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Part 8: RNG Design Review

Analog RNG Approach

Components:
  - 555 Timer (oscillator)
  - Capacitor (variable timing)
  - Comparator (analog to digital)
  - LED/Display (output)

Key Principle:
  Physical phenomena (capacitor discharge timing)
  create unpredictable voltages that appear random.

Randomness Source:
  Environmental factors, component tolerances,
  and human reaction time

Digital RNG Approach

Components:
  - 555 Timer (clock ~1kHz)
  - Binary Counter (74LS90 or 74LS93)
  - BCD-to-Seven-Segment Decoder (74LS47)
  - Seven-Segment Display
  - Push Button (stop)
  - Debounce Circuit

Key Principle:
  Rapid counting stopped at random human moment
  produces unpredictable values.

Randomness Source:
  Human reaction time variability (~150-300ms)

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Part 9: Practice Assessment Problems

Problem Set 1: Basic Calculations

1. What is the current through a 1kΩ resistor connected to 5V?

2. Convert 47kΩ to ohms: ___

3. Convert 0.022µF to picofarads: ___

4. What binary value is 14 decimal? ___

5. What decimal value is 1001₂? ___

Show Solutions

1. I = V/R = 5V/1000Ω = 0.005A = 5mA

2. 47kΩ = 47,000Ω

3. 0.022µF = 22,000pF = 22nF = 22,000,000pF... wait
   0.022µF × 1,000,000 = 22,000 pF = 22nF

4. 14 = 1110₂

5. 1001₂ = (1×8) + (0×4) + (0×2) + (1×1) = 9₁₀

Problem Set 2: Circuit Analysis

6. Three 100Ω resistors are connected in series. What is the total resistance?

7. Three 100Ω resistors are connected in parallel. What is the total resistance?

8. Calculate the frequency output of a 555 timer with R = 10kΩ and C = 100µF.

Show Solutions

6. Series: Rtotal = 100 + 100 + 100 = 300Ω

7. Parallel: 1/Rtotal = 1/100 + 1/100 + 1/100 = 3/100
   Rtotal = 100/3 = 33.3Ω

8. f = 1.443 ÷ (R × C)
   f = 1.443 ÷ (10,000 × 0.0001)
   f = 1.443 ÷ 1
   f = 1.443 Hz

Problem Set 3: Safety and Documentation

9. Which class of fire extinguisher should you use for an electrical fire?

10. List two things to check before applying power to a circuit.

Show Solutions

9. Class C fire extinguisher (or ABC multi-purpose)

10. Any TWO of:
    - All connections are correct and secure
    - No shorts between adjacent pins
    - Power supply voltage is correct
    - Components are placed correctly (watch polarity)
    - No damaged components
    - Work area is clean and organized

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Part 10: Self-Assessment Checklist

Use this checklist to rate your understanding of each topic:

┌─────────────────────────────────────────────────────────────────┐
│                  UNIT 1 SELF-ASSESSMENT                         │
├─────────────────────────────────────────────────────────────────┤
│                                                                 │
│  Rate each topic:                                               │
│    4 = I can teach this to someone else                         │
│    3 = I understand this well                                    │
│    2 = I understand the basics                                   │
│    1 = I need more study                                        │
│    0 = I don't understand this                                   │
│                                                                 │
│  TOPIC                                    SCORE    NEED WORK?  │
│  ─────────────────────────────────────────────────────────────  │
│  Safety Rules                            ___ /4     □ Yes □ No  │
│  Electrical Hazards                      ___ /4     □ Yes □ No  │
│  Resistor Color Codes                    ___ /4     □ Yes □ No  │
│  Ohm's Law Calculations                  ___ /4     □ Yes □ No  │
│  Series/Parallel Circuits                ___ /4     □ Yes □ No  │
│  KVL and KCL                            ___ /4     □ Yes □ No  │
│  Scientific/Engineering Notation         ___ /4     □ Yes □ No  │
│  Binary to Decimal Conversion           ___ /4     □ Yes □ No  │
│  Decimal to Binary Conversion           ___ /4     □ Yes □ No  │
│  Analog vs Digital Signals              ___ /4     □ Yes □ No  │
│  ADC Concept                            ___ /4     □ Yes □ No  │
│  555 Timer Operation                    ___ /4     □ Yes □ No  │
│  Clock Signal Parameters                ___ /4     □ Yes □ No  │
│  Breadboarding Techniques               ___ /4     □ Yes □ No  │
│  Engineering Design Process             ___ /4     □ Yes □ No  │
│  Analog RNG Design                      ___ /4     □ Yes □ No  │
│  Digital RNG Design                      ___ /4     □ Yes □ No  │
│                                                                 │
│  TOTAL SCORE: ___ / 68                                          │
│                                                                 │
│  Target Score: 56+ (80% minimum for mastery)                    │
│                                                                 │
└─────────────────────────────────────────────────────────────────┘

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Part 11: Preparing for Unit 2

Unit 2 will build on everything you've learned in Unit 1:

Topics Coming Next

Unit 2 Topic	Unit 1 Foundation
Logic Gates	Boolean algebra, truth tables
Combinational Logic	Binary number systems
Sequential Logic	Clock signals, flip-flops
Counters and Registers	Binary counters, timing
Schematic Entry	Breadboarding, documentation
PLD Programming	Logic fundamentals

Skills to Practice

Before starting Unit 2, make sure you can:

• [ ] Calculate voltage, current, and resistance using Ohm's Law
• [ ] Convert between decimal and binary
• [ ] Read resistor color codes without hesitation
• [ ] Build a circuit on breadboard from a schematic
• [ ] Use an oscilloscope to measure signals
• [ ] Document your work following engineering standards

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Summary

Unit 1 covered the essential foundations for digital electronics:

1. Safety — Your wellbeing is the top priority in the lab
2. Components — Analog (resistors, capacitors) and digital (gates, ICs)
3. Circuits — Ohm's Law, series/parallel, KVL/KCL
4. Notation — Scientific notation and SI prefixes
5. Binary — The language of digital systems
6. Signals — Analog vs digital, ADC concepts
7. Timing — 555 timer, clock signals, frequency
8. Design — Engineering process, RNG project

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Key Reminders for Unit 2

• Always prioritize safety in everything you do
• Build on your math skills—circuits require calculations
• Practice binary conversions until they're automatic
• Documentation and testing are essential engineering skills
• Ask questions when you're uncertain—engineering is collaborative
• Review Unit 1 material before starting Unit 2

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Custom activity — adapted from PLTW Digital Electronics