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Rain falls through the funnel to here

When the bucket tips  the rain falls in the other side

Hack a Rain Gauge

Water is essential for life and rainfall is an essential part of replenishing our water resources.  In our homes we use water for drinking, washing and watering the garden, etc.  So in understanding how we use water in relation to rainfall we can be better informed consumers and minimise our environmental impact.  We can use rainfall data in many other ways for example design rainwater harvesting systems and to know when we need to water the vegetable patch.

HUM-DRUM RAIN GAUGE

Here is my rain gauge sat in my garden ready to be hacked.

Let start by looking at how the rain gauge works


Monitoring rainfall is fundamental to understanding our environment

Like a lot of people I have a rain gauge in my garden that I brought for £25 (or $xx).  Unfortunately it doesn’t do exactly what I want – a great reason for a hacking project.
I have is a tipping bucket rain gauge.  The tipping buck system consists of two buckets on a see-saw that sits under a funnel.  

Rain falls into the funnel and then into one of the buckets.  When the bucket is full the see-saw tips and the other bucket sits under the funnel and the water in the first bucket drains out.  This continues all time that it is raining. (Let’s call the time it rains a rainfall event).  When the rainfall event is over we can count up the number of times the bucket system has tipped, and if we know the volume of rain in the bucket when it tips then we know the volume of rain that fell on the device during the storm.  (To work out the size of the bucket I recommend carefully tipping a known volume of water into the rain gauge, count the number of tips and divide the volume by this value.  For this I normally use a syringe because

INSIDE THE RAIN GAUGE

The rain gauge has a plastic funnel that catches the rain and directs it into one of two buckets sat on a see-saw.  Here is what the rain gauge looks like with the outer cover removed.  The rectangular block contains the electronics.  The sticky up bit contains the radio transmitter

My gauge measures rainfall by counting how many times a small bucket fills

they have a measuring scale on the sides that tend to be quite accurate).  
In addition as we know the size of the funnel we can work out the amount of rain falling on any area, be it our garden or our roof.  Engineers express this in terms of the
amount falling on an area of 1m2, and call the resulting value the rainfall intensity with units of millimetres/hour.
The rainfall intensity is usually given in units of mm/hour.  We can work this out since we know that the storm lasted for 2 hours.

If this was the only rainfall event that day we could present the information as,

Daily rainfall = 2mm
Average daily rainfall intensity = 2 mm/24 hours = 0.08 mm/h

The rain gauge unit in my garden sends this data via a 433Hz radio signal to a unit indoors.  The indoor unit displays the total rainfall per day and presents the historical daily data on a simple graphical interface.

So what’s the problem?

Next Step

© Flow RC June 2014

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