NCEA Level 2 Digital Technologies cheat sheet

IPO model: every program decomposes into Input (read data), Process (sequence, selection, iteration), Output (display or store results); name the three parts when describing a solution.

Three control structures: sequence runs statements in order; selection uses if/elif/else or switch; iteration uses while (test before body, may run zero times) or for (known count or collection traversal).

Boolean operators: AND is true only if both operands are true; OR is true if at least one is true; NOT inverts; evaluate NOT before AND before OR unless brackets override.

Modular design: a function/method takes parameters, returns a value, and hides internal detail; passing by value copies the data, so the caller's variable is unchanged after the call.

Testing types: unit tests check one function in isolation, integration tests check modules together, and boundary tests use values at the edges (0, 1, max, max+1) where errors cluster.

Debugging aids: a trace table records variable values after each line; a breakpoint pauses execution; print or log statements reveal intermediate state.

Variable scope: a local variable exists only inside its function; a global variable is visible throughout the module, and modifying it inside a function risks unintended side effects.

Data structures: arrays/lists store ordered items accessed by index (0-based in Python and Java); dictionaries/maps store key-value pairs accessed by key; strings are immutable sequences of characters.

Sorting and searching: linear search checks each item in turn (works on unsorted data); binary search halves a sorted list each step and is much faster but requires sorted input.

Ohm's law: V = I × R, so current I = V/R and resistance R = V/I; power P = V × I = I²R = V²/R, in watts.

Series circuits: one path, so current is the same everywhere and resistances add (R_total = R1 + R2); voltage divides across components.

Parallel circuits: voltage is the same across each branch and current splits; total resistance is 1/R_total = 1/R1 + 1/R2, always less than the smallest branch resistance.

Digital logic: an AND gate outputs 1 only when all inputs are 1; OR outputs 1 when any input is 1; NOT inverts; XOR outputs 1 when inputs differ.

Microcontroller anatomy: CPU, memory (program and data), and input/output pins; a program stored in memory reads sensors, decides, and drives actuators in a loop.

Sensor and actuator types: sensors convert physical quantities to electrical signals (LDR for light, thermistor for temperature, push button, ultrasonic distance); actuators act on the world (LED, buzzer, motor, servo, relay).

Analogue versus digital: real-world signals are continuous; a microcontroller reads analogue input through an ADC (e.g. 10-bit giving 0-1023) and outputs PWM to approximate analogue levels such as LED brightness or motor speed.

Pull-up and pull-down resistors hold an input pin at a defined high or low level so a floating pin does not read randomly when a switch is open.

Embedded system constraints: limited memory, processing power, and power supply, so code is kept small, uses interrupts rather than busy-waiting, and favours low-power sleep modes.

Data versus information: data is raw symbols (e.g. 21, 'A'); information is data processed into meaning for a purpose, such as an average or a report.

Number bases: binary is base 2, decimal base 10, hexadecimal base 16; one hex digit represents exactly four binary bits, so 1111 1010 = FA.

Units: 1 byte = 8 bits; 1 KB = 1024 bytes; 1 MB = 1024 KB; 1 GB = 1024 MB; 1 TB = 1024 GB.

Character encoding: ASCII uses 7 bits for 128 characters; Unicode/UTF-8 covers all world scripts, with UTF-8 using 1-4 bytes per character.

Compression: lossless (e.g. PNG, ZIP) reconstructs the original exactly; lossy (e.g. JPEG, MP3) permanently discards data to shrink file size.

Database structure: a table holds records (rows); each record has fields (columns); a primary key uniquely identifies a record; a foreign key references a primary key in another table.

SQL basics: SELECT fields FROM table WHERE condition; ORDER BY sorts results; JOIN combines related tables on a matching key; INSERT, UPDATE, DELETE modify data.

Data validation versus verification: validation checks format or range rules (type, length, range, presence); verification confirms accuracy by double entry or proofreading.

Threats and controls: malware, phishing, and unauthorised access are countered by strong authentication, encryption, firewalls, and regular backups; personal data is protected under privacy principles.

Raster versus vector: raster images are grids of pixels and lose quality when enlarged; vector graphics use mathematical paths and scale without pixelation.

Resolution and file size: image file size ≈ width × height × colour depth ÷ 8 bytes; a 1000 × 1000 pixel image at 24-bit colour is about 3 MB uncompressed.

Colour depth: 1 bit = 2 colours, 8 bit = 256 colours, 24 bit = 16,777,216 colours (true colour), split into 8-bit red, green, and blue channels.

Image formats: JPEG is lossy and suited to photographs; PNG is lossless with alpha transparency; GIF is limited to 256 colours but supports simple animation; SVG is vector.

Audio: sample rate is samples per second (CD quality 44.1 kHz) and bit depth is bits per sample (16-bit); file size ≈ sample rate × bit depth × channels × seconds ÷ 8.

Video: frame rate is frames per second; file size ≈ width × height × colour depth × frame rate × seconds, so resolution and frame rate drive size.

Design principles: contrast, alignment, repetition, and proximity (CARP) guide layout; visual hierarchy directs the eye with size, colour, and placement.

Storyboarding and wireframes plan a media product before production; the design cycle is plan, design, produce, test, and evaluate against the brief.

Copyright: original media is automatically protected; using others' images, audio, or video requires permission or a licence such as Creative Commons, and the source must be credited.