EC-19.1 What Electronic Systems Do, and the Five Blocks

What this is and why it exists

This is the map the rest of the area fills in.

Without it, the courses that follow look like five unrelated subjects a reader is asked to trust will connect later. With it, each one arrives with somewhere to go. The measurements course is the sensing block. The embedded course is the computing block. The networks course is the communicating block. The electrical energy course is the powering block.

The model here is not deep. It is a frame, and its value is that it is available from the first afternoon rather than assembled in hindsight after three years.

The vocabulary

• System — a collection of parts arranged to do something the parts alone do not.
• Sensor — a component that turns a physical quantity into an electrical one.
• Transducer — the general word for a component that converts between two forms of energy.
• Actuator — a component that turns an electrical quantity back into a physical effect.
• Controller — the part that applies a rule between the input and the output.
• Interface — the boundary where two blocks meet and agree what passes between them.
• Embedded system — a computing part built into a product rather than sold as a computer.
• Signal — the carrier of information between blocks.
• Power supply — the block that provides energy to all the others.

The mental model

Almost every electronic product is built from five kinds of block, and it is worth being able to name them for anything you pick up.

Sensing. Something physical becomes an electrical quantity. Temperature, light, pressure, sound, motion and position all have components that do this. What the conversion costs in accuracy, in speed and in noise is the whole content of the measurements course later on.

Computing. Between the input and the output sits something that applies a rule. It can be a single component, a small circuit, or a processor running code. Which of those is appropriate is a design decision with real consequences for cost, power and how hard the product is to change.

Actuating. A decision becomes a physical effect again. A motor turns, a heater warms, a speaker moves air, a screen lights. Actuators nearly always need more power than the computing part can supply, which is why the two are rarely wired directly together.

Communicating. Information leaves the product or arrives at it. This can be a wire to another board, a radio link, or a connection to a network. It is invisible in a product description and takes a surprising share of the design effort.

Powering. Energy has to reach every other block at the voltage each one needs. Batteries, converters and regulators live here. This block is where products fail in the field more often than a beginner expects.

Two things are worth saying about the model rather than the blocks.

The first is that the interfaces are where the design difficulty lives. Each block on its own is usually a solved problem with a component you can buy. What goes wrong is the boundary. A sensor produces a smaller voltage than the computing part can read, or an actuator draws a current the supply cannot deliver. The engineering design course later has a whole topic on why systems fail at the joins.

The second is that the blocks are functions rather than parts. One integrated circuit can carry three of them. One block can be spread across several components. Naming the function first and finding parts second is the order that works. Starting from a part you happen to have produces a device looking for a purpose.

The exercise that makes this stick is taking a product you own and naming its five blocks. A digital thermometer, a set of wireless earphones, a washing machine. Doing it two or three times turns the model from a diagram into a habit. That habit is what the rest of the area is built on.

What you should now be able to explain or do

• Name the five functional blocks and say what each contributes to a product.
• Take an ordinary electronic device and identify its blocks from the outside.
• Explain why an actuator is rarely wired directly to the computing part.
• Say why the interfaces between blocks are where most design difficulty appears.
• Explain why a block is a function rather than a component.
• Say which later course in this area owns each block.

Check yourself