Resource Cheatsheet
Code: Communicating Around Corners
Code ch. 5 — signalling by wire between houses: circuits need a return path, shared commons and earth grounds, and why long wires dim the signal.
- Updated
- Reading time
- 2 min read
- Detail
- Code (2nd ed.)
- Detail
- Ch. 5
On this page
In one line: once line of sight fails, wires carry the signal — but every circuit needs a way back, and long wires fight you with resistance.
Companion to: Charles Petzold, Code (2nd edition), chapter 5.
Wiring a signal between two places
| Problem | Solution |
|---|---|
| Every circuit needs a return path | Run a second wire back |
| Two-way signalling doubles the wiring | Share one common return wire between both circuits |
| Even the common wire costs money over miles | Use the earth itself as the return (a ground connection at each end) |
| Long wires have resistance, so the bulb dims | Use thicker wire, a higher voltage, or regenerate the signal (next chapter) |
- Resistance grows with length and falls with thickness.
- Wire gauge (AWG): a lower number means thicker wire. Cat6 cable is typically 23 AWG, Cat5e 24 AWG.
Key terms
| Term | Meaning |
|---|---|
| Common | A shared connection that several circuits use as their return |
| Ground / earth | A reference point at 0 V; historically the literal earth |
| Voltage drop | Voltage lost along a wire because of its resistance |
| Attenuation | A signal weakening over distance |
🔐 Security and IT connections
- Distance limits come from this chapter. Copper Ethernet tops out at 100 m because of attenuation. Beyond that you need a switch (which regenerates the signal) or fibre.
- PoE loses power over long runs. That’s why PoE budgets assume some voltage drop along the cable.
- Grounding is safety. The earth pin on a plug gives fault current a safe path. ESD straps clip to ground for the same reason.
- Serial links share a signal ground (RS-232 console cables to switches and routers): without a common reference, a “1” can’t be told from a “0”.
Practice drills
1. Two friends each want to signal the other. Why does a shared common wire save cabling?
Both circuits can use one return wire, so you need three wires instead of four.
2. A 130 m Ethernet run is flaky. Why, and what fixes it?
It exceeds the 100 m copper limit and the signal attenuates. Add a switch midway, or use fibre.
3. Which is thicker: 22 AWG or 26 AWG?
22 AWG — a lower gauge number means thicker wire.
Key takeaways
- Every circuit needs a return path; a shared common or earth ground saves wire.
- Resistance grows with wire length, causing voltage drop and signal loss.
- Distance limits, grounding and signal regeneration in networking all trace back here.