The Rain Caller

Someone in every household has this job: watch the washing line. Not officially. Nobody assigns it. But someone always ends up doing it — checking the sky between tasks, going to the window when the light changes, carrying laundry in before it rains. In many homes this is the same person every time, and that person has opinions about it. The problem is that rain does not announce itself. It does not send a message. It does not build up gradually — not always. In a good monsoon, the sky goes from white to grey to water in less than ten minutes. The person who went to make tea comes back to wet sheets. What this situation needs is not more vigilance. Vigilance is exhausting. It needs a machine. Specifically: a machine that sits outside, next to the washing line, and makes a very loud noise inside the house the moment — the very first moment — it detects a drop of rain. Not when it's heavy. Not when a puddle forms. Not when it's obvious. The first drop. A rain sensor is a small board covered in two sets of conductive tracks that almost touch — separated by tiny gaps. In dry air, no current flows across the gaps. The moment a drop of water lands and bridges a gap, current flows. That tiny current can be amplified, compared to a threshold, and turned into a signal that fires a buzzer. Today, your team is going to build one.