Solution Alternatives

One-sentence summary

We learn to produce more than one way to solve the same problem, to see the pros and cons of each, and to choose the best one based on criteria.

Why does it matter?

The first idea that comes to mind is often mistaken for the only idea. Yet the same problem usually has several possible solutions, and not all of them work equally well.

In the previous lesson we prepared a requirements list: we wrote down, point by point, what the project needs to do. Now we take a step forward. With clear requirements in hand, we will generate different routes to the same goal and compare them.

Getting stuck on the first idea creates two risks. We may miss an easier or cheaper route. Or we may notice a weakness in the idea far too late, right in the middle of building. Comparing a few alternatives on paper first saves both time and materials.

This lesson is not a new programming topic. It is a way of thinking and deciding; an approach that engineers, designers and good project teams use every day.

Producing several solutions to the same problem

The first step in solving a problem is to produce as many ideas as possible. At this stage we do not eliminate ideas straight away; we multiply them first. This is called brainstorming.

Throughout this lesson we will follow a single example project from start to finish: a night light that turns on by itself when it gets dark. This is a student-scale project, familiar from earlier modules.

Suppose our requirements list says:

• The light should turn on automatically when the room gets dark.
• It should stay off when there is enough light.
• It should be safe to use in a child's room.
• It should run on a battery or USB; no wall-socket cable.

Let us think of several different solutions that meet the same requirements:

1. Light-sensor (LDR) lamp: It measures how bright the room is and turns the LED on in the dark.
2. Motion-sensor (PIR) lamp: It lights up for a few minutes when there is movement in the room, then switches off.
3. Timer lamp: It turns on at a set time and switches off at a set time in the morning.
4. Manual lamp: It is turned on and off with a button; it is not automatic.

All four are an answer to the problem "give light when the room is dark." But they do not all fit the requirements to the same degree. To see this, we need to compare them.

Everyday example: Ways to get to school

We can see the same idea in a problem that has nothing to do with robotics. The problem: getting to school in the morning. The alternatives:

• Walking
• Cycling
• Taking a bus or school shuttle

All three get you to school. But as distance, weather, safety and time change, so does the "best" route. Walking on a rainy day and cycling over a short sunny distance are very different choices. What matters is not defending one route by habit, but comparing them against the conditions.

The pros and cons of each solution

Every solution has strengths and weaknesses. A perfect solution almost never exists; every choice means giving something up. That is why it helps to write ideas side by side as pros and cons.

Let us examine two of the night-light ideas this way.

Solution 1: Light-sensor (LDR) lamp
Pros:
  + Works fully automatically
  + Needs few parts, so it is cheap
  + Lights up only when it is really dark, saving battery
Cons:
  - The sensor needs to be adjusted correctly
  - It can be fooled if light shines directly on it

Solution 2: Motion-sensor (PIR) lamp
Pros:
  + Stays off when nobody is there, using very little battery
  + Handy when you get up at night and it lights up on movement
Cons:
  - Switches off while you sleep still, so it is a poor night light
  - The sensor and circuit are a little more complex

Writing this out makes one thing clear: the motion-sensor lamp looks clever, but it does not quite match our requirement. We asked for "a soft, steady light in the dark"; the PIR works on the logic of "light up when there is movement." In other words, a bright idea can be bright for the wrong problem.

Everyday example: Making a classroom poster

Imagine you are making a classroom poster. The alternatives: drawing it by hand, printing it from a computer, or cutting out and gluing ready-made pictures. Hand drawing is original but takes a long time. Printing is fast but needs a printer and ink. Cut-and-paste is easy but risks using other people's images without permission. As you can see, each route gives you something while making you give up something else.

Choosing based on criteria

Once we have seen the pros and cons, it is time to choose. But saying "I think this one is better" is not enough. We base the choice on criteria. A criterion is a standard that lets us judge all the solutions with the same eye.

Let us set a few criteria for the night-light project:

• Cost: Is it cheap or expensive?
• Ease: How hard is it to build and program?
• Energy: How carefully does it use the battery?
• Fit: How well does it match the requirements list?
• Safety: Is it safe in a child's room?

Now let us compare the four solutions against these criteria in a table. We give each criterion a score from 1 (weak) to 3 (good). This table takes the earlier comparison one step further and builds a bridge to the method we will use in more detail in the "Comparing Solutions" lesson.

The table is a thinking tool, not an absolute truth. But it makes the choice visible and open to discussion. In this example the light-sensor lamp reaches the highest total, because it works automatically, is cheap and fits the requirements best.

Criteria are not the same in every project

One thing to watch: the criteria and their order of importance change from project to project. In some projects cost is the most important criterion, while in another speed or safety comes first. If you consider one criterion more important than another, you can strengthen the table by giving it double points (weighting it). What matters is deciding on the criteria before making the choice, not shaping them afterwards to produce the answer we already wanted.

Mini practice

Produce and compare alternatives for a small project of your own. For example: "a system that warns you when a plant's soil is dry," or "a setup that reminds you when you forget your bag at the door."

Follow these steps:

1. Write the problem in a single sentence.
2. Produce at least three different solution ideas. Do not eliminate any of them yet.
3. Write at least one pro and one con for each solution.
4. Set three to five criteria (such as cost, ease, energy, fit, safety).
5. Fill in the blank table below and give each criterion a score from 1 to 3.

Problem: ______________________________________

| Solution   | Crit.1 | Crit.2 | Crit.3 | Total  |
|------------|--------|--------|--------|--------|
| Solution A |        |        |        |        |
| Solution B |        |        |        |        |
| Solution C |        |        |        |        |

Chosen solution: ______________________________
Reason for choosing: __________________________

After filling in the table, ask yourself: does the highest-scoring solution actually feel sensible? If it does not, you may have left out one of the criteria.

Common mistakes

Getting stuck on a single idea

Starting to build the first solution that comes to mind is a common mistake. You cannot compare without producing at least two or three alternatives.

Choosing the criteria afterwards

First picking the solution you want, then writing criteria to justify it, is not a real comparison. Criteria must be set before the choice.

Looking at only one criterion

"This one is the cheapest" is not enough. If the cheapest solution does not meet the requirements at all, it may actually be the most expensive choice, because you will have to start over in the end.

Ignoring the cons

Avoiding the cons of an idea we like only saves that weakness for the building stage. An honest list of pros and cons prevents bad surprises.

Safety note

When comparing solutions, safety should always be one of the criteria. No matter how cheap or clever an idea looks, if it is not safe it should stay at the bottom of the table. In electronics projects, do not use mains electricity (the wall socket); prefer batteries, USB or low voltage. Always assess and build any solution that involves soldering, cutting tools or hot surfaces together with an adult.

Lesson summary

• The same problem usually has more than one solution; we multiply ideas first, then eliminate.
• The real picture appears once the pros and cons of each solution are written side by side.
• The choice should rest on criteria set in advance, not on personal preference.
• A comparison table scores solutions with the same eye and makes the choice visible.
• Criteria and their order of importance can change in every project; safety is always one of them.

Check questions

1. Why should we not eliminate ideas straight away during brainstorming?
2. What is the point of writing a solution's pros and cons side by side?
3. What is a criterion, and why should it be set before the choice?
4. In the comparison table, why did the light-sensor solution get the highest score for the night light?
5. Why can the sentence "the cheapest solution is always the best" be wrong?

Answers

1. Because the aim of this stage is to multiply the options. If we eliminate too early, we may lose an idea that could turn out to be better. Elimination comes later, using criteria.
2. It lets us see the strengths and weaknesses of each solution at the same time. That way we notice a weakness early, on paper, instead of during the building stage.
3. A criterion is a standard that lets us judge all the solutions with the same eye (such as cost, ease or safety). It is set before the choice; otherwise we risk inventing criteria that produce the answer we already wanted.
4. Because it works automatically, is cheap since it needs few parts, and fits the requirements list (a soft, steady light in the dark) best. It had the highest total score.
5. Because a cheap solution is useless if it does not meet the requirements. It may end up costing more, since you might have to start over. That is why looking at a single criterion is not enough.

Source and verification note

For “Solution Alternatives”, verification focuses on whether the relationship between Producing several solutions to the same problem and The pros and cons of each solution remains consistent across examples. A project page should make a result claim only when it is supported by a real prototype, test record or observation. Numbers such as cost, duration and success rate must be labelled clearly when they are estimates.

Next lesson

Sketch and Flowchart: Planning the solution we chose, step by step, with a draft and a flowchart before we start building.