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, especially regarding durability during deployment, and we found their musings most helpful while iterating our own design.

The Challenge

Due to its exposed position, a rain gauge must resist multiple simultaneous environmental onslaughts:

• The sun beats down mercilessly on an exposed rain gauge. And it has to be exposed, to do its job. Two main solar mechanisms conspire to limit its lifetime:
  • UV - ultraviolet radiation breaks down molecular bonds, often leading to embrittlement of especially plastics, even ones supposedly UV-resistant. Living at altitude, as we do, aggravates this, but nonetheless we desire many years of trouble-free operation, not mere months.
  • Heat - can stress electronics, lead to warping and binding of the mechanism, or leakage of water into areas where it should not go.
• Arthropods - insects and arachnids, to be specific: both ants and spiders have been found in previous versions. Especially spiders would move in and affix the moving seesaw to the base with their silky creations during the dry months, thereby disabling the gauge completely. 
• Vertebrates - birds poo everywhere, and may even consider nesting in the funnel, although we have not yet run into the latter problem. At least we never had problems with snakes, as in the link above.
• Leaves and other wind-borne debris, which can block or clog the funnel.
• Weather - in addition to the expected falling water (i.e. rain) around here we also get:
  • Hail - the gauge should be able to resist at least medium-sized hailstones. That is in fact how we learned that a previous collecting funnel had become brittle due to UV:  a short hailstorm, involving quite small hailstones, left it in tatters, despite it having spent less than a year outside. Most disappointing.
  • Wind - the mounting should be sturdy enough to resist wind forces, and the wind should also not be able to enter via the funnel or the drainage holes and somehow affect the tipping mechanism.
  • Lightning - often associated with rain around here, care must be taken that it does not lead to false triggers, or damage to electronics.
  • I have no idea how to handle snow. We don't do that around here. Perhaps a deep funnel, with tall vertical walls, to capture and keep the snow until it gets around to melting?
• Moisture - well, rain is wet, yes, but when electricity and especially electronics are involved, care must be taken to ensure that never the twain shall meet. And corrosion of metal parts means that stainless steel is probably a good idea for things like fasteners and axles. The link in the first paragraph above mentions even aluminium funnels succumbing to corrosion under their (admittedly extreme) tropical conditions.

It took multiple iterations to address most of the challenges listed above, and no doubt more lessons will be learned along the way, but we are pleased to present our latest incarnation for public consumption at last.

The History

Since the heady days of Covid lockdowns we were monitoring our rainfall using a Misol-type tipping bucket rain gauge, harvested from a defunct weather station. It triggers a magnetic reed switch each time the tipping bucket toggles, so a D1 mini ESP board, running Tasmota counts these events and reports them on the wifi network using MQTT. With Home Assistant in charge this means that we can monitor our rainfall in real time and also make decisions based on this information; primarily whether to run or inhibit the irrigation system.

The Misol sensor is surprisingly stout, but its native resolution is a bit over 0.3 mm of rainfall per tip, which is an uncomfortable size, being neither here nor there for those of a decimal orientation. So we increased the catchment area by printing (in vase mode, oh goody!) an extension...