A Proper Printed Precision Pluviometer

While making a tipping bucket rain gauge is in principle fairly straightforward, making it robust and durable yet sensitive is not, as we learned the hard way. Others have even more experience, and we found their musings most helpful while iterating our own design.

Full project details, including history, assembly, and calibration guidelines can be found at https://hackaday.io/project/202925.

Due to its exposed position, a rain gauge must resist multiple simultaneous environmental onslaughts, not only from the weather, but also from diverse fauna and flora conspiring to repurpose and compromise its operation.

Printing 

The printed parts are seven in total, all carefully configured for various printing options in the .3mf files attached hereto.

• RainGaugeTipper – Printed at about 0.1mm layer height, with supports only in the cavities for the hub insert and the magnet.
• RainGaugeHub – Printed without supports, but with a brim, to improve bed adhesion.
• RainGaugeBottom – Printed without supports, with variable layer height. To facilitate easy assembly, an XY Size Compensation of -0.1 mm was used. This ensures that the top, the shield, the inner cover, and the screws can easily be fitted on, around, and in it respectively.
• RainGaugeInnerCover – No supports, and 0.3mm layer height. Variable layer height, actually, but because of its simplicity only the first and last layers are thinner.
• RainGaugeShield – As with the previous part, the variable layer height used mostly 0.3 mm. Supports are needed on the inner edge at the bottom, due to the horizontal step.
• RainGaugeTop – Variable layer height, printed without supports, except for the five mounting holes at the far end of the arm. You do not want or need supports in the thread for the funnel, or the grooves on the bottom face – it would be a nightmare to remove, and quite superfluous.
• RainGaugeFunnel – This one is printed in vase mode, at 0.2 mm layer height, with no top or bottom layers. Even though the nozzle is 0.4 mm wide, the extrusion width is set at 1 mm, to ensure a decent stiffness and strength. There are two sizes, with catchment diameters of approximately 125 mm and 150 mm respectively. You only need one, depending on the desired sensitivity.

We used PETG throughout – ASA should also work. The top and the shield was printed in white, which should hopefully reflect much of the sunlight, keeping temperatures in check, and possibly extending its lifetime. The funnel is white too, although it will be covered in adhesive metal foil anyway, so the colour is probably moot.

In addition to the printed parts, we also used: 

• A neodymium magnet. This design uses a 6mm round magnet, 2mm in thickness, but other sizes can also work - it simply has to be able to trigger the Hall sensor as it passes by, while not being too heavy; its weight is a not-insignificant fraction of the entire moving part, into which it is pressed, taking into account the required polarity for the Hall effect sensor.
• Stainless steel bolts: M4 x 12mm. You need 8 of those - two for the adjustable end stops, and six more (which can be shorter, say M4 x 8mm, if you prefer) to close everything up. Or they can be long too – it is just more work to screw them in.
• One stainless steel sewing pin, at least 26mm in length, to serve as the axle of the tipping mechanism. If it is too long you can simply snip off the sharp end after installation. In previous projects we proved the value of sewing pin axles under similar circumstances.
• An optional but highly desirable stainless steel drain strainer, ~5.4 cm in diameter, to keep leaves, branches, and bugs at bay. (Try the four-letter Eastern bazaar starting with ‘T’ and ending with ‘U’.)

• Adhesive aluminium tape (search for “High-Temp Resistant Aluminum Foil Tape”). The width is unimportant, as you will do some complex patchwork with it anyway, to cover and protect the funnel both inside and out.

• A Hall effect sensor. We used a venerable A3144E Hall Effect Sensor, because it is digital (latching), cheap, and universally available (though supposedly obsolete). Or you could use some alternatives: A1120, US1881, A1104, MH182 - there is a plethora of similar sensors in the ultra-mini UA SIP package. 

• Something to monitor the Hall effect sensor, and report on changes. We are pervasively Home Assistantified, therefore a small ESP-based wifi board running the redoubtable Tasmota code was our choice. The dry space should be ample – even a Sonoff Basic can fit in there.

Full assembly details, extending to software setup and integration into Home Assistant, can be found at https://hackaday.io/project/202925.