Evolution of Wired Communication Systems

Key Insight

To enable communication beyond direct line of sight, such as between two houses whose windows do not face each other, simple wired electrical circuits can be constructed. Initially, a one-way system involves connecting a battery and switch in one location to a lightbulb in another using two wires. Closing the switch illuminates the lightbulb, enabling Morse code communication. For bidirectional communication, two such independent circuits can be established, allowing each person to send messages simultaneously, though reading and sending at the same time can be challenging.

The wire requirement for a bidirectional system can be reduced by 25 percent by connecting the negative terminals of the two batteries, creating a 'common' connection. This configuration joins the two separate circuits, now requiring only three wires instead of four. When one switch is depressed, electricity flows through that specific circuit, utilizing the common connection but not causing current to flow through the common section itself if only one circuit is active. This demonstrates an initial optimization in wire usage, allowing the two circular circuits (battery to switch to bulb to battery) to operate independently while joined.

Further wire reduction is possible by utilizing Earth as a massive electrical conductor, replacing one of the wires, especially in high-voltage systems. An electrical connection to the Earth, called a 'ground' (in America) or 'earth' (in Great Britain), involves a substantial conductor like an 8-foot long, 0.5-inch diameter copper pole buried in the ground, providing 150 square inches of contact. The Earth acts as a virtually limitless source and repository for electrons, effectively completing the circuit by allowing electrons to flow from the negative battery terminal into the ground and from the ground into the friend's house to complete the circuit. This allows for a two-way Morse code system with just two wires between houses for high-voltage setups, an important step in freeing communication from line-of-sight and distance limitations.