Auto Rain Gauge

By Andy Yeh 2025

These days, it is too easy to get weather/climate information but too often we take that for granted and ignore the understanding about weather. For example, what do we measure about the weather? What does it mean 5 mm of rain fall? What does it mean about 20% chance of rain today? What temperature do we feel good? What is a good and healthy humidity? What is the relationship between temperature and humidity? What are the effects of high and low air pressure and what is its unit? How about wind speed and direction? and solar radiation and UV index? What instruments do we use to measure them?

As part of the Weather / Climate inquiry in the weather station project, how do we measure the amount of rain is a good STEM project for schools. Traditionally, we use a rain gauge such as these in the Bunnings, install in open area in the backyard to catch the rain, then manually record the amount of rain water in the rain gauge on daily basis during raining days.

Rain gauge with two cylinders. The ourter one enables more catchment of rain. The inner one collect rain from the top funnel. It has mm reading marks of calibrated height/intervals.

To test, we can use a measuring cup filled with 100 mL of water. 100 mL could be converted as 100 cc (cubic centimeter). 100 cc is 100,000 cubic millimeter (1 cc is equal to 1000 mm^3)

We can then pour in the 100 mL through the top funnel and see how many mm of rain the inner cyliner would measure. Note that the funnel is round and has a diameter of 120 mm.

Then we can open the lid funnel and take out the inner cylinder to see how it measures. And it measures about 8.8 mm (of rain). Do you know why?

The traditional rain gauge requires manual reading and recording. But what about if the rain gauge is installed in the school or outback where we have an interest in knowing the rainfall in those areas but we do not have regular access to them? The modern automatics rain gauge is a smart and simple design to address this and it is widely used these days everywhere and in the smart Personal Weather Station. In our weather station project, we can see the auto rain gauge has the tipping/flipping buckets design. Inspired by Christopher Barnatt's video below, I have 3D printed and made some auto rain gauges with some improvements.

In EUB452, some pre-service teachers are interested in creating integrated STEM education project for students to foucs on the science of rain fall and data literacy to measure and test accuracy of instrument.

If you are interested in making one, you will need the following parts:

3D models to print - https://www.thingiverse.com/thing:7351606
3D models to tinker if you wish - https://www.tinkercad.com/things/8FuyuVYSh6x-auto-rain-gauge-share
Electronic components: Arduino nano R3, Nano shield, LCD1602 I2C module, some dupont cables/wires, some M3 / M4 screws, a Reed switch, small magnet.
Arduino program for this project can be downloaded here.

Please leave a comment below or ask questions if any.

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