Electronics & Microcontrollers Guide

The brains, sensors, actuators, and power systems that bring junkyard builds to life.

This guide covers the electronic components and microcontroller platforms used across builds. If a build has code, sensors, or blinking lights, the parts are listed here.

Microcontroller Platforms

Raspberry Pi

A full Linux computer the size of a credit card. Runs Python, has GPIO pins for hardware control, and handles tasks like image processing, audio analysis, and web serving that would choke an Arduino.

When to use a Pi: When you need to run Python scripts, process images or audio, serve a web interface, or do anything that requires an operating system. If you're running OpenCV, a web server, or complex logic — use a Pi.

Used in builds:

• Fireworks Sequencer — GPIO relay control
• Smart Mirror — web display
• Retro Arcade Cabinet — emulation
• Pi DJ Controller — audio processing
• Pi-Hole Ad Blocker — DNS server
• Face Tracking Laser — OpenCV processing
• Music Visualizer LED Wall — audio FFT + LED control
• All Python Projects category builds

Arduino

An open-source microcontroller board. No operating system — it runs one program (sketch) in a loop. Dead simple, real-time, and perfect for hardware control tasks that don't need an OS.

When to use an Arduino: When you need real-time hardware control without the overhead of an operating system. Reading sensors, driving motors, controlling relays, running LED animations. If the task is "read input, do thing, repeat" — use an Arduino.

Used in builds:

• Arduino Guitar Pedal — real-time audio DSP
• Auto Plant Watering — sensor reading + relay control
• Arduino Breathalyzer — MQ sensor reading
• LED Cube 8x8x8 — high-speed LED multiplexing
• MIDI Stepper Organ — precise stepper timing
• Nerf Sentry Turret — servo control
• EMF Ghost Detector — analog sensing

ESP32

A WiFi + Bluetooth microcontroller that costs less than a coffee. The sweet spot between Arduino simplicity and Pi connectivity. Programmable with the Arduino IDE, MicroPython, or ESP-IDF.

When to use an ESP32: When you need WiFi or Bluetooth connectivity, or when the project needs more processing power than an Arduino but doesn't need a full OS. Mesh networks, IoT sensors, wireless controllers, and camera projects are ESP32 territory.

Used in builds:

• ESP32 Mesh Walkie-Talkie — mesh WiFi communication
• ESP32-CAM Security — video streaming
• ESP32 Weather Station — sensor data over WiFi
• ESP32 Micro Drone — flight controller
• Star Tracker — stepper motor control with mobile app

When to Use Which

Common Sensors

BME280 — Temperature, Humidity, Pressure

What it does: Measures temperature (-40 to +85°C), humidity (0-100%), and barometric pressure (300-1100 hPa) in a single tiny module. Communicates via I2C or SPI.

Approximate cost: $3-5

Used in builds: ESP32 Weather Station, Fermentation Chamber

MPU6050 — Accelerometer + Gyroscope

What it does: 6-axis inertial measurement unit (3-axis accelerometer + 3-axis gyroscope). Detects motion, tilt, rotation, and vibration. I2C interface.

Approximate cost: $2-4

Used in builds: Earthquake Detector, ESP32 Micro Drone, Body Pose Music

HC-SR04 — Ultrasonic Distance Sensor

What it does: Measures distance (2-400 cm) by sending ultrasonic pulses and timing the echo. Accuracy ~3mm. Simple trigger/echo interface — no library needed.

Approximate cost: $1-3

Used in builds: Nerf Sentry Turret (proximity detection), general obstacle avoidance

MQ Series — Gas Sensors

What it does: A family of metal-oxide semiconductor gas sensors. Different models detect different gases:

• MQ-2: Combustible gas, smoke
• MQ-3: Alcohol vapor
• MQ-7: Carbon monoxide
• MQ-135: Air quality (NH3, benzene, smoke)

Approximate cost: $2-5 each

Used in builds: Arduino Breathalyzer (MQ-3), environmental monitoring

Soil Moisture Sensor

What it does: Measures the moisture content of soil using either resistive (cheap, corrodes fast) or capacitive (better, lasts longer) probes. Outputs analog voltage proportional to moisture.

Approximate cost: $1-3 (resistive), $3-5 (capacitive)

Used in builds: Auto Plant Watering

Photoresistors (LDR)

What it does: A resistor whose resistance changes with light intensity. Bright light = low resistance, darkness = high resistance. The simplest light sensor possible.

Approximate cost: $0.10-0.50 each (usually sold in packs of 20-50)

Used in builds: Star Tracker (ambient light detection), various light-activated builds

Actuators

Servo Motors

What they do: Rotate to a specific angle (0-180° typically) and hold position. Controlled by PWM signal. Available in micro (SG90, 9g) and standard (MG996R, 55g metal gear) sizes.

Approximate cost: $2-3 (micro), $5-8 (standard metal gear)

Used in builds: Face Tracking Laser, Nerf Sentry Turret, Star Tracker

Power note: ALWAYS power servos from a separate 5V supply, not from the microcontroller's 5V pin. Servos draw current spikes that cause brownouts and resets.

Stepper Motors

What they do: Rotate in precise, discrete steps (typically 200 steps per revolution = 1.8° per step). Can be microstepped to 1/16 or 1/32 step for smoother motion. Require a driver board (A4988, DRV8825, or TMC2209).

Approximate cost: $5-15 (NEMA 17), free (salvaged from printers — see Appliance Teardown Guide)

Used in builds: Printer Stepper CNC, Pen Plotter, MIDI Stepper Organ, Printer Robot Arm, Motorized Camera Slider

Relay Modules

What they do: Electrically controlled switches. A low-voltage signal (3.3V or 5V) from a microcontroller switches a high-voltage/high-current circuit (up to 250V AC, 10A typically). Available in 1, 2, 4, 8, and 16 channel modules.

Approximate cost: $2-3 (single), $5-8 (8-channel), $8-12 (16-channel)

Used in builds: Fireworks Sequencer, Auto Plant Watering, Sentiment Room Lighting, Voice Home Automation

Safety note: When switching mains voltage (120V/240V) through relays, use optically isolated relay modules. Verify the relay is rated for the voltage and current you're switching. Use proper wire gauge and connectors — not breadboard jumper wires.

Displays

OLED 0.96" (SSD1306)

What it is: A tiny 128x64 pixel monochrome OLED display. Bright, sharp, readable in direct sunlight. I2C interface — only needs 2 data pins.

Approximate cost: $3-5

Used in builds: ESP32 Weather Station, Arduino Breathalyzer, EMF Ghost Detector

LED Matrices

What they are: Grids of LEDs in 8x8 or larger configurations. The MAX7219 driver handles multiplexing for you. Chain multiple modules for scrolling text displays.

Approximate cost: $3-5 per 8x8 module (with MAX7219 driver)

Used in builds: LED Cube 8x8x8

Neopixel / WS2812B LED Strips

What they are: Individually addressable RGB LED strips. Each LED has its own controller chip — you can set any LED to any color independently. One data wire controls the entire strip. Available in various densities (30, 60, 144 LEDs/meter).

Approximate cost: $5-10 per meter (30 LEDs/m), $10-20 per meter (60 LEDs/m)

Used in builds: Music Visualizer LED Wall, LED Cube 8x8x8, Sentiment Room Lighting

Power note: Each LED draws up to 60mA at full white. A strip of 300 LEDs can draw 18A. Use a beefy 5V power supply and inject power at multiple points along the strip to prevent voltage drop. Use a level shifter (3.3V to 5V) when driving from ESP32 or Pi.

Power

5V Power Supplies

What they do: Convert wall AC to regulated 5V DC for microcontrollers, LEDs, and low-voltage electronics.

Common sources:

• USB phone chargers (5V 1-3A) — good for Pi, Arduino, small builds
• Mean Well LRS-50-5 (5V 10A) — good for LED strips
• Repurposed ATX computer power supplies (5V 20A+) — free and overpowered

Approximate cost: $0 (salvaged charger) to $15 (dedicated 5V 10A supply)

12V Power Supplies

What they do: Power motors, relay coils, LED strips (12V variant), solenoids, and fans.

Common sources:

• Old laptop chargers (12-19V, 3-5A) — often close enough to 12V
• LED strip power supplies (12V 5-30A)
• Repurposed ATX computer power supplies (12V 15A+)

Approximate cost: $0 (salvaged) to $15 (dedicated supply)

LiPo Batteries

What they are: Lithium polymer battery packs. Lightweight, high energy density, high discharge rates. Common in RC hobby (drones, cars). Rated by voltage (cell count: 1S=3.7V, 2S=7.4V, 3S=11.1V) and capacity (mAh).

Approximate cost: $10-30 depending on capacity and cell count

Used in builds: ESP32 Micro Drone, portable builds

Safety note: LiPo batteries can catch fire if overcharged, over-discharged, punctured, or short-circuited. Always use with a proper BMS or charger. Store in a LiPo-safe bag. Never charge unattended.

TP4056 Charger Boards

What they are: Single-cell lithium-ion/LiPo charger modules with micro-USB input. Charges one 3.7V cell safely with overcharge and overdischarge protection (when using the version with protection circuit).

Approximate cost: $0.50-1 each (often sold in packs of 5-10)

Used in builds: Any portable build powered by a single lithium cell. Laptop Battery Power Bank

Audio

INMP441 — I2S MEMS Microphone

What it is: A digital microphone module that communicates via I2S protocol. Clean audio capture without the noise of analog microphones. Works directly with ESP32 and Raspberry Pi.

Approximate cost: $3-5

Used in builds: ESP32 Mesh Walkie-Talkie, Earthquake Detector (vibration as audio), audio capture projects

Speakers

What they are: Electromagnetic transducers that convert electrical signals into sound. Salvage from dead electronics (laptops, TVs, phones) or buy small 8-ohm speakers for $1-3.

Approximate cost: $0 (salvaged) to $3 (purchased)

Used in builds: Hard Drive Speaker, Pirate Radio, audio output for any build

Piezo Buzzers

What they are: Simple tone generators. Apply voltage and they beep. Available as active (built-in oscillator, just needs power) or passive (needs a frequency signal, can play tones).

Approximate cost: $0.50-1 each

Used in builds: Alert/notification sounds across many builds, EMF Ghost Detector

Buying Guide Summary

Essential Tools for Electronics Work

You don't need a lot, but you do need these:

• Soldering iron — Hakko FX-888D ($100) is the gold standard. Budget: any temperature-controlled iron ($20-30).
• Multimeter — Measures voltage, current, resistance, continuity. A $15 meter from Amazon handles 95% of needs.
• Breadboard and jumper wires — For prototyping before soldering. Buy an assortment pack.
• Wire strippers — Self-adjusting type saves time and frustration.
• Heat shrink tubing — Assortment pack. Better than electrical tape for permanent connections.
• Third-hand/helping hands tool — Holds components while you solder.
• USB-to-serial adapter — For programming Arduino clones and ESP32 boards that don't have built-in USB.