What we are making: a plan on one page, signed off before anybody picks up a wire.

The brief

Build a machine that senses something, decides something, and does something. It has to work without you explaining it. It has to use parts from your own box. And it has to be finished, on a table, working, in session 28.

That is the whole brief. It is deliberately wide, and the difficulty is entirely in your hands — a careful simple thing that works beats an ambitious thing that does not, every time, and the marking says so.

Three that have worked before

1. A parking sensor. Ultrasonic in, buzzer and screen out. Beeps faster the closer you get. Everybody understands it in two seconds.
2. A plant minder. Soil moisture in, screen and LED out. Tells you when to water it, and the threshold is yours to defend.
3. A combination lock. Keypad in, servo out. Right code, the latch swings open.

Write these five things down

1. The sentence. ‘When the input does this, the output does that.’ One sentence. If you cannot write it, you do not have an idea yet.
2. The parts. List them. Every one must be in your box or in the spares tray.
3. The number. What is the threshold, and how will you decide it? ‘I will measure it in session 25’ is a perfectly good answer.
4. The order. What are you building first? The answer is always the input.
5. The risk. What is most likely to go wrong, and what will you do instead?

Before you leave

• Your five answers, written in your notebook.
• Your teacher's signature on the plan.
• Your parts checked out and in your tray.