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.

When to Use This Skill

• User asks to "create a breadboard layout" or "mockup a circuit"
• User wants to visualize component placement on a breadboard
• User needs a visual reference for building a 6502 computer
• User asks to "draw a circuit" or "diagram electronics"
• User wants to create educational electronics visuals
• User mentions Ben Eater tutorials or retro computing projects
• User asks to mockup 555 timer circuits or LED projects
• User needs to visualize wire connections between components

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

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

Creating a 555 Timer Circuit

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

Creating a 6502 Microprocessor Layout

1. Place W65C02S centered on breadboard
2. Add 28C256 EEPROM for program storage
3. Place W65C22 VIA for I/O
4. Add 7400-series logic for address decoding
5. Wire address bus (A0-A15)
6. Wire data bus (D0-D7)
7. Connect control signals (R/W, PHI2, RESB)
8. 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

Build Examples

Build 1 — Single LED

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

Steps:

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

Build 2 — 555 Astable Blinker

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

Steps:

1. Place 555 IC straddling center channel
2. Connect pin 1 to GND, pin 8 to +5V
3. Connect pin 4 to pin 8 (disable reset)
4. Wire 10kΩ between pin 7 and +5V
5. Wire 100kΩ between pins 6 and 7
6. Wire 10µF between pin 6 and GND
7. Connect pin 3 (output) to LED circuit

Troubleshooting

Issue	Solution
LED doesn't light	Check polarity (anode to +, cathode to -)
Circuit doesn't power	Verify power rail connections
IC not working	Check VCC and GND pin connections
555 not oscillating	Verify threshold/trigger capacitor wiring
Microprocessor stuck	Check RESB is HIGH after reset pulse

References

Detailed component specifications are available in the bundled reference files:

• 555.md - Complete 555 timer IC specification
• 6502.md - MOS 6502 microprocessor details
• 6522.md - W65C22 VIA interface adapter
• 28256-eeprom.md - AT28C256 EEPROM specification
• 6C62256.md - 62256 SRAM details
• 7400-series.md - TTL logic gate pinouts
• assembly-compiler.md - Assembly compiler specification
• assembly-language.md - Assembly language specification
• basic-electronic-components.md - Resistors, capacitors, switches
• breadboard.md - Breadboard specifications
• common-breadboard-components.md - Comprehensive component reference
• connecting-electronic-components.md - Step-by-step build guides
• emulator-28256-eeprom.md - Emulating 28256-eeprom specification