What it shows
Three plastic cups on a spindle spin in the wind and a magnet on the spindle passes a Hall sensor once a turn. The Arduino times the pulses to compute wind speed, reads a potentiometer on a wind vane for direction, and shows both on an OLED.
The science
The cups catch more wind on their open side than their back, so they rotate at a rate proportional to wind speed. The Hall sensor switches when the magnet passes, and an interrupt counts the pulses; speed is turns per second times the circumference of the cup circle times a correction factor found by calibration. The vane turns the potentiometer shaft, and analogRead gives an angle from 0 to about 300 degrees, mapped to compass points.
Materials
Cost: under Rs 500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An Arduino Uno or Nano clone and USB cable
- An A3144 Hall sensor module and a small magnet
- Three paper or plastic cups, a bottle, a bearing or an old pen body for the spindle
- A 10 kΩ potentiometer and a cardboard vane
- A 0.96 inch I2C OLED
- A 9 V battery and jumper wires
- A quiet open path, a tape measure and a stopwatch for calibration
Safety
For this project: Calibrate by carrying the anemometer at a steady walking pace on a quiet open path in still air, with an adult nearby; never hold it out of a car window or ride a bicycle with it. Keep small magnets away from children.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
9 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Fix the three cups evenly on spokes around the spindle so they all face the same way round.
Mount the spindle so it spins freely; glue the magnet near the bottom and fix the Hall sensor 3 mm from its path.
Wire the Hall module OUT to pin 2 with INPUT_PULLUP, VCC and GND; attach an interrupt on FALLING.
Mount the vane on the potentiometer shaft and wire the pot to 5 V, GND and A0.
Every second, read the pulse count, zero it, and compute turns per second.
Convert to speed: 2 times pi times the arm radius times turns per second, then multiply by a factor of about 2 to 3 found by calibration.
Calibrate by walking at a measured pace (distance over time) in still air and adjusting the factor until the display matches.
Map the vane reading to N, NE, E and so on and mark the base with the real north using a phone compass.
Show speed in km per hour and direction on the OLED and log readings over an afternoon.
What you should see
The OLED shows wind speed and direction; the calibrated reading matches a known walking speed to within about 15 percent.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why do the cups spin the same way whatever the wind direction?
The open cup always catches more force than the rounded back of the opposite cup.
02What does a Hall sensor detect?
A magnetic field; the A3144 switches its output when the field is strong enough.
03Why is a calibration factor needed?
The cups turn slower than the wind because of drag and bearing friction.
04Why is the potentiometer limited to about 300 degrees?
Its track does not go all the way round; a real vane uses a magnetic angle sensor.
Take it further
Add a BMP180 pressure sensor and an ESP8266 to upload a full weather record online.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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