# CS4FN Advent – Day 6 – patterned bauble: tracing patterns in computing – printed circuit boards, spotting links and a puzzle for tourists

Welcome to Day 6 of the CS4FN Christmas Computing Advent Calendar – every day until Christmas we’ll post a little something about computer science. Some of it will even relate (…vaguely) to the picture on the advent calendar’s door.

Today’s picture is of a festive bauble with a pattern engraved on it. That obviously made us think of printed circuit boards. Read on to see why.

At the very end of this article you can see a list of all the previous Advent Calendar posts.

## Printed Circuit Boards

Yesterday we looked at computers made of water, in which the flow of water (and where it ends up) let people do some quite advanced calculations. Today it’s the electrons that are doing the flowing… through tiny little copper channels.

Printed Circuit Boards (aka PCBs) contain and connect the bits that computers and electronic devices need to run properly. PCBs have two main functions: to act as a sort of ‘bookshelf’ for all the electronic components (such as transistors, sensors etc), but also to support electrical connections between those components so that electricity can flow through them and the device can work. Some of the components are soldered directly to the board, others are connected by being clipped into sockets that have previously been attached. A circuit board is generally only a few inches long with smaller ones for smaller (or simpler) devices – they have to fit inside after all.

They look like the image above and generally consist of a stiff flat board (which itself does not conduct electricity) and on that there’s a coating of copper foil which has had a pattern etched into it. Etching uses chemicals to ‘delete’ all the bits of copper that aren’t needed, leaving behind only the pattern that forms the correct connecting circuits.

## Complete circuit

This next article was originally published on the CS4FN website.

1. Kirchhoff’s famous circuit laws describe the conservation of charge and energy in electrical circuits. They form the basis for circuit design as well, leading to many a homework assignment working out the current at different places in a circuit. Their creator, physicist Gustav Kirchhoff, was born in the town of Koenigsberg in what is now Russia.

2. Koenigsberg sits on several islands originally connected by seven bridges. It was this town plan that helped mathematician Leonhard Euler to pose and solve the famous Seven Bridges of Koenigsberg Problem. It helped develop the useful mathematical area called graph theory.

3. Graph theory is used by engineers when building mobile phone networks. Your mobile phone finds the nearest base station and locks onto it to send and receive information. Researchers recently revealed a midget drone plane called WASP, built on the cheap with parts bought on the Internet. It could fly unseen over a city mimicking a ‘local tower’ to intercept phone messages and wi-fi data.

4. Wi-fi is a set of agreed standards that allow radio links between all manner of electronic gadgets. These worldwide rules are based around the idea of ‘frames’. Frames contain the data that is to be sent or received in a particular format. Devices have to know these rules of conversation to talk to each other. They range from asking nicely in the ‘association request frame’ if the receiver is ready, willing and able to connect, to the ‘association response frame’ where the receiver answers “yes” or “no”.

5. Yes or no is an example of a binary encoding: only two options exist. Many electronic devices these days use binary coding. The signal has only two possible values. That makes turning them mathematically into numbers and the subsequent calculations easier and more accurate. Analogue electronics, where voltage and currents can vary across a range of values are more difficult to design but are still useful in some applications. They can have surprising advantages. For example, before digital radio took over it was possible to build a working ‘crystal radio set’ using analogue techniques with simple household items like wire and a rusty nail. This radio was powered by the radio waves and didn’t need batteries.

6. Batteries store energy and many see them as a big unsolved problem of electronics. They are heavy, need space and charging, and when they run out your gadget stops. Researchers are now looking at using common everyday stuff like plastics and concrete to store the energy we need. Another idea is to use energy from our walking on the go. Whatever way energy is created and stored in the future, it will still swirl round the circuit obeying Kirchhoff’s laws.

GO TO 1!

## Today’s puzzle

Instead of an electron whizzing around a circuit board imagine you’re a tourist guide looking after some guests visiting London. Your task is to get your group to visit each one of the visitor attractions listed in the printed circuit ‘map’ below, once (without revisiting it). Can you plan a route that does this? (The answer will be in tomorrow’s advent calendar ‘door’).

Note for parents and teachers: we have a classroom activity that features this puzzle and teachers can use this to talk about things like an introduction to algorithmic thinking, sequences, graphs / nodes / edges, representation and abstraction. Access The Tour Guide activity here (the image above comes from the free PDF which you can download on that page).