Understanding Switch Logic

Let’s start with the basics of electricity and electronics. Computers use power. Knowing the basics of power flow and switch logic helps you to understand not only the computer, but also computational processes.

Your takeaways from this episode:

• Power flows when there is a complete circuit and path
• Power flows from the voltage source (V) to the physical rod that is connected to earth ground
• When a relay coil is powered on, the switch is physically pulled to the on state
• Relays are the foundation of both software and computer circuitry

Study Notes

Why Switch Logic?

In this topic, we introduce switch logic. Why do you need to understand switches?

1. Computer circuit boards work on switch logic
2. Software works on switch logic

Electricity 101

We’re going to start with a very basic understanding of electricity before we get into the gates.

Earlier in this series, we introduced you to switches under the premise of binary (remember the switch on your wall that turns the light bulb on or off?)

However, there’s more to the light in your room than just “on” and “off.”

Power flow

Power comes from a source. This source could be a gas-powered generator, or hydropower, or a nuclear power plant. A power source is any component that supplies energy.

Power comes through wires and is carried to your home. From there, it goes into a circuit box and travels through wires and into the lights, electronics, etc. in your home.

For power to flow, it needs to be grounded.

Power flows from the power source to the earth ground.

In an “on” or “closed” state, the power circuit is connected from the source to the ground. Power can flow.

However, in an “off” or “open” state, the switch breaks the circuit and removes the contact with the ground. Since the power is no longer grounded, power cannot flow.

Basics of Relay Logic

When the relay is “on” there’s continuous flow to the ground. When a coil in a relay turns on, it becomes magnetized and pulls the relay down, switching the state of the relay.

Power can’t flow downstream through to the light that’s off, because it’s not a complete circuit.

Your CPU has a bunch of tiny circuits-and these are all just small switches. We call them transistors, but they are actually just relays with switches inside.