Hack a Rain Gauge - Project Stage 6

Improving the accuracy - 3rd Prototype

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It may be possible to reduce the size of the buckets but the easiest way to increase the accuracy of the rain gauge is to increase the catchment area.  In this project we have fixed a large funnel (approx. diameter 25cm) to the rain gauge.  First we had to saw off a few centimetres from the spout to ensure that it sat nicely inside the existing unit.  This increases the catchment area from 0.0095 m2 to 0.049m2 and increase of more than 5.  Be careful though the unit is now more susceptible to being blown over.  Make sure that it is secured at the base.

We also noted that the rain often formed droplet that stuck to the side of the funnel.  These droplets can become quite large before gravity takes them down into the tipping bucket.  

To reduce this we coated the inside of the funnel with Teflon.  This may sound slightly space age.  In fact all we did was cut a cone shape from a sheet of Teflon cooking mat and tape it in place.

The improvement in accuracy can be seen from the graph below of a similar rainfall event as that shown before.  The graph is still a step graph but the size of the steps has been significantly reduced giving us a much better idea of the pattern of rainfall.

We’ll round of with a list of the parts, consumables and tools we used


Often the drops collect on the surface of the funnel before running down into the bucket.


Here is the final design of the rain gauge....for now.


Here is a graph of the second set of results.  You can hopefully see that the graph shows more detail and the steps are smaller.

Parts list

Rain gauge

Arduino Uno

Adafruit SD card shield (and SD card)

Reed switch

Project enclosure

Battery pack & batteries


Teflon cooking mat


Hook-up wire


Duck tape

Perf board


Terminal blocks


Soldering Iron

Wire cutters


© Flow RC June 2014

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