Legacy Circuit Mockups

A skill for creating breadboard circuit mockups and visual diagrams for retro computing and electronics projects. This skill leverages HTML5 Canvas drawing mechanisms to render interactive circuit layouts featuring vintage components like the 6502 microprocessor, 555 timer ICs, EEPROMs, and 7400-series logic gates.

Leverage native parallel subagent dispatch and 200k+ context windows where available.

When to Use This Skill

Use symptom -> action triggers: when one matches, apply this skill and verify with the protocol below.

User asks to create a breadboard layout or circuit mockup
User wants visualized component placement for legacy electronics
User needs diagrams for 6502, 555 timer, EEPROM, VIA, or 7400-series builds
User asks for educational electronics visuals or wiring diagrams
User is following retro-computing tutorials and needs visual references

Prerequisites

Understanding of component pinouts from bundled reference files
Knowledge of breadboard layout conventions (rows, columns, power rails)

Supported Components

Microprocessors & Memory

Component	Pins	Description
W65C02S	40-pin DIP	8-bit microprocessor with 16-bit address bus
28C256	28-pin DIP	32KB parallel EEPROM
W65C22	40-pin DIP	Versatile Interface Adapter (VIA)
62256	28-pin DIP	32KB static RAM

Logic & Timer ICs

Component	Pins	Description
NE555	8-pin DIP	Timer IC for timing and oscillation
7400	14-pin DIP	Quad 2-input NAND gate
7402	14-pin DIP	Quad 2-input NOR gate
7404	14-pin DIP	Hex inverter (NOT gate)
7408	14-pin DIP	Quad 2-input AND gate
7432	14-pin DIP	Quad 2-input OR gate

Passive & Active Components

Component	Description
LED	Light emitting diode (various colors)
Resistor	Current limiting (configurable values)
Capacitor	Filtering and timing (ceramic/electrolytic)
Crystal	Clock oscillator
Switch	Toggle switch (latching)
Button	Momentary push button
Potentiometer	Variable resistor
Photoresistor	Light-dependent resistor

Grid System

// Standard breadboard grid: 20px spacing
const gridSize = 20;
const cellX = Math.floor(x / gridSize) * gridSize;
const cellY = Math.floor(y / gridSize) * gridSize;

Component Rendering Pattern

// All components follow this structure:
{
  type: 'component-type',
  x: gridX,
  y: gridY,
  width: componentWidth,
  height: componentHeight,
  rotation: 0,  // 0, 90, 180, 270
  properties: { /* component-specific data */ }
}

Wire Connections

// Wire connection format:
{
  start: { x: startX, y: startY },
  end: { x: endX, y: endY },
  color: '#ff0000'  // Wire color coding
}

Step-by-Step Workflows

Creating a Basic LED Circuit Mockup

Define breadboard dimensions and grid
Place power rail connections (+5V and GND)
Add LED component with anode/cathode orientation
Place current-limiting resistor
Draw wire connections between components
Add labels and annotations

Creating a 555 Timer Circuit

Place NE555 IC on breadboard (pins 1-4 left, 5-8 right)
Connect pin 1 (GND) to ground rail
Connect pin 8 (Vcc) to power rail
Add timing resistors and capacitors
Wire trigger and threshold connections
Connect output to LED or other load

Creating a 6502 Microprocessor Layout

Place W65C02S centered on breadboard
Add 28C256 EEPROM for program storage
Place W65C22 VIA for I/O
Add 7400-series logic for address decoding
Wire address bus (A0-A15)
Wire data bus (D0-D7)
Connect control signals (R/W, PHI2, RESB)
Add reset button and clock crystal

Component Pinout Quick Reference

555 Timer (8-pin DIP)

Pin	Name	Function
1	GND	Ground (0V)
2	TRIG	Trigger (< 1/3 Vcc starts timing)
3	OUT	Output (source/sink 200mA)
4	RESET	Active-low reset
5	CTRL	Control voltage (bypass with 10nF)
6	THR	Threshold (> 2/3 Vcc resets)
7	DIS	Discharge (open collector)
8	Vcc	Supply (+4.5V to +16V)

W65C02S (40-pin DIP) - Key Pins

Pin	Name	Function
8	VDD	Power supply
21	VSS	Ground
37	PHI2	System clock input
40	RESB	Active-low reset
34	RWB	Read/Write signal
9-25	A0-A15	Address bus
26-33	D0-D7	Data bus

28C256 EEPROM (28-pin DIP) - Key Pins

Pin	Name	Function
14	GND	Ground
28	VCC	Power supply
20	CE	Chip enable (active-low)
22	OE	Output enable (active-low)
27	WE	Write enable (active-low)
1-10, 21-26	A0-A14	Address inputs
11-19	I/O0-I/O7	Data bus

Formulas Reference

Resistor Calculations

Ohm's Law: V = I × R
LED Current: R = (Vcc - Vled) / Iled
Power: P = V × I = I² × R

555 Timer Formulas

Astable Mode:

Frequency: f = 1.44 / ((R1 + 2×R2) × C)
High time: t₁ = 0.693 × (R1 + R2) × C
Low time: t₂ = 0.693 × R2 × C
Duty cycle: D = (R1 + R2) / (R1 + 2×R2) × 100%

Monostable Mode:

Pulse width: T = 1.1 × R × C

Capacitor Calculations

Capacitive reactance: Xc = 1 / (2πfC)
Energy stored: E = ½ × C × V²

Color Coding Conventions

Wire Colors

Color	Purpose
Red	+5V / Power
Black	Ground
Yellow	Clock / Timing
Blue	Address bus
Green	Data bus
Orange	Control signals
White	General purpose

LED Colors

Color	Forward Voltage
Red	1.8V - 2.2V
Green	2.0V - 2.2V
Yellow	2.0V - 2.2V
Blue	3.0V - 3.5V
White	3.0V - 3.5V

Cross-Client Portability

This skill is written to stay usable across GitHub Copilot, Claude Code, and Codex.

GitHub Copilot: keep the folder in a Copilot-visible skill path or wrap the workflow in project instructions when folder discovery is unavailable.
Claude Code: keep the folder in a local skills directory or a compatible plugin source.
Codex: install or sync the folder into $CODEX_HOME/skills/legacy-circuit-mockups and restart Codex after major changes.

MCP Availability And Fallback

Preferred MCP Server: None required

Fallback prompt: "Use the Legacy Circuit Mockups skill without MCP. Rely on its local instructions, bundled resources, standard shell or editor tools, and direct verification. Show the evidence used before concluding."
Do not claim an MCP operation was used when the active host does not expose it.
Treat local files, tests, rendered outputs, logs, or screenshots as the fallback evidence path.

Anti-Patterns

Starting from a generic template without adapting it: The output may look polished but still miss the real audience or medium.
Ignoring final render or export review: Layout bugs often appear only after the asset is opened in its destination tool.
Fixing content and presentation in one pass: It becomes hard to tell whether a problem is structural or visual.

Verification Protocol

Before claiming "skill applied successfully":

Pass/fail: The Legacy Circuit Mockups implementation names the target runtime, framework version, and affected files.
Pass/fail: Build, lint, test, or equivalent local validation is run for the changed surface.
Pass/fail: Edge cases for errors, dependency drift, and environment differences are addressed or explicitly out of scope.
Pressure-test scenario: Apply the workflow to a change that passes happy-path tests but fails one boundary condition.
Success metric: Zero untested success claims; every implementation claim maps to a command or artifact.

Build Examples

Build 1 — Single LED

Components: Red LED, 220Ω resistor, jumper wires, power source

Steps:

Insert black jumper wire from power GND to row A5
Insert red jumper wire from power +5V to row J5
Place LED with cathode (short leg) in row aligned with GND
Place 220Ω resistor between power and LED anode

Build 2 — 555 Astable Blinker

Components: NE555, LED, resistors (10kΩ, 100kΩ), capacitor (10µF)