Wire #

Connects components on the breadboard. Breadpad models real wire properties including resistance, temperature coefficients, and tolerances for accurate simulations.

Basic Properties #

• Terminals: 2 (Start and End points)
• SPICE Designation: RW (resistor) or E (VCVS for ideal)
• Default Diameter: 0.65mm (22 AWG)
• Automatic Resistance: Calculated from length and material

Key Parameters #

Physical Properties #

• Diameter: Wire thickness in meters

  • Common: 0.65mm (22 AWG), 0.81mm (20 AWG)
  • Affects resistance calculation

• Resistivity: Material property (Ω·m)

  • Copper: 1.68e-8 Ω·m (default)
  • Aluminum: 2.82e-8 Ω·m
  • Gold: 2.44e-8 Ω·m
  • Silver: 1.59e-8 Ω·m

Electrical Properties #

• Resistance: Auto-calculated using:

  R = ρ × L / A
  Where:
  - ρ = resistivity
  - L = length + 0.8 (connection factor)
  - A = πr² (cross-sectional area)
  

• Temperature Coefficients

  • TC1: Linear coefficient (3900 ppm/°C for copper)
  • TC2: Quadratic coefficient (usually 0)

• Tolerance: Manufacturing variation

  • Typical: 1-5% for diameter
  • Affects resistance calculation

Visual Properties #

• Color Options:
  • Primary (automatic based on connection)
  • Black (ground)
  • Red (power)
  • Blue, Green, Yellow, Orange, Purple, White

SPICE Implementation #

Breadpad uses two models depending on resistance:

Standard Wire (R ≥ 1µΩ) #

RW1 node1 node2 0.015 TC1=0.0039 TC2=0

Ideal Wire (R < 1µΩ) #

For numerical stability:

VW1 node1 n_int 0     ; Dummy voltage source
EW1 n_int node2 node1 n_int 1  ; Unity-gain VCVS

Wire Gauge Reference #

Common Breadboard Wires #

Power and Ground Wires #

Length Calculation #

Breadpad automatically calculates wire length:

• Breadboard spacing: 0.1" (2.54mm)
• Manhattan distance: |x₂-x₁| + |y₂-y₁|
• Connection overhead: +0.8 units

Resistance Effects #

Voltage Drop #

V_drop = I × R_wire

Example: 22 AWG, 10cm length, 1A current

• R = 52.9 mΩ/m × 0.1m = 5.29 mΩ
• V_drop = 1A × 5.29mΩ = 5.29 mV

Power Loss #

P_loss = I² × R_wire

Temperature Rise #

Resistance increases with temperature:

R(T) = R₂₅ × (1 + α(T - 25°C))

Where α = 0.0039/°C for copper

Color Coding Best Practices #

Power Distribution #

• Red: Positive voltage (VCC, VDD)
• Black: Ground (GND, VSS)
• Yellow: Alternative positive (e.g., 3.3V)
• Blue: Negative voltage (VEE)

Signal Wires #

• Green: Data/signal lines
• White: Clock signals
• Orange: Control signals
• Purple: Special/debug signals

Automatic Coloring #

Breadpad automatically assigns colors when:

• Connected to voltage source positive → Red
• Connected to ground → Black
• Otherwise → Primary color

Design Considerations #

Current Capacity #

Derate by 50% for reliability:

• 22 AWG: Use for < 0.5A
• 20 AWG: Use for < 0.75A
• 18 AWG: Use for < 1.2A

High-Frequency Effects #

Not modeled but important above 10MHz:

• Skin effect increases resistance
• Inductance: ~1nH per mm
• Capacitance: ~0.1pF per mm

Thermocouple Effects #

Dissimilar metals create thermocouples:

• Copper-to-brass: ~3µV/°C
• Important for precision measurements

Simulation Tips #

1. Short Wires: Can usually ignore resistance
2. Power Wires: Always model resistance for accuracy
3. High Current: Check voltage drop and heating
4. Monte Carlo: Include tolerance for worst-case
5. Temperature: Use TC1 for thermal analysis
6. Star Grounding: Minimize ground loops

Parasitic Effects #

For critical simulations, consider:

* Complete wire model
RW1 1 2 0.015        ; Resistance  
LW1 2 3 10n          ; Inductance
CW1 1 0 0.1p         ; Capacitance to ground
CW2 3 0 0.1p

Troubleshooting #

High Resistance Connections #

• Check for corrosion
• Verify wire gauge
• Consider contact resistance

Voltage Drop Issues #

• Use thicker wire (lower AWG)
• Shorten wire runs
• Parallel multiple wires

Noise Pickup #

• Keep wires short
• Use twisted pairs
• Add bypass capacitors

See Also #

• Resistor - For explicit resistance
• Transmission Line - For distributed effects
• Voltage Source - For power distribution
• Capacitor - For bypass and filtering