ZoneFlow

A cheap DIY rain gauge for ZoneFlow: Misol bucket + Aqara Zigbee sensor

2026-09-29

Rain-aware watering is one of ZoneFlow's headline tricks — it holds off, or skips a cycle outright, if it's already rained. But that only works when something in your yard is actually measuring rain, in millimetres, in real time. A weather API's forecast is a guess about rain that hasn't happened yet; ZoneFlow wants to know about rain that already fell in your yard.

A proper tipping-bucket rain gauge does that job well, and the mechanism itself is cheap: a small funnel drains into a two-sided seesaw bucket, and every time one side fills and tips, a magnet swings past a reed switch. Count the tips, multiply by however many millimetres each tip represents, and you have real rainfall. The expensive part of a commercial weather station is everything around that mechanism — the radio, the battery, the console. This build skips all of it by piggybacking on hardware you may already own.

What you'll need

  • A Misol-style tipping-bucket rain gauge — the plastic funnel-and-seesaw mechanism sold under the Misol, Ambient Weather and Fine Offset family of clone weather stations. You want the mechanical gauge itself, not a full weather-station console.
  • An Aqara Zigbee Door and Window Sensor (the small two-piece contact sensor). It already has a battery, a reed switch and a Zigbee radio built in — that's the whole point of using it.
  • A small screwdriver, some thin wire, and a soldering iron if you want a tidy joint rather than a twist-and-tape one.
  • Kafuter K-705 (or a similar clear RTV silicone sold for electronics — see the weatherproofing note below).
  • A Zigbee coordinator already paired with Home Assistant.

How the hack works

Both halves of this build already contain a reed switch and a magnet — the gauge's seesaw trips one every time it tips, and the Aqara sensor's own contact mechanism uses the same principle to sense a door opening. The hack is simply to let the gauge's reed switch, instead of the Aqara sensor's own magnet, be the thing that closes the Aqara sensor's contact.

Open the gauge's small electronics housing and find the two wires coming off its internal reed switch — normally they'd run to a weather-station console. Open the Aqara sensor and bridge those same two wires onto its own reed-switch leads, in place of (or in parallel with) its magnet. Every tip of the bucket now reads to Home Assistant exactly like a door opening and closing, except it's really a fixed, tiny slug of rainwater going by.

Because the Aqara sensor supplies its own battery and its own Zigbee radio, there's no wiring back to the house and nothing else to power — you're reusing a sensor that was probably sitting in a drawer.

Here's a walkthrough of one build showing the wiring in detail:

Wiring it into Home Assistant

Once the Aqara sensor reports open and closed on every tip, count the transitions with a simple automation or a template or utility-meter sensor, and multiply by your gauge's millimetres-per-tip rating. Misol-style buckets commonly work out to somewhere around 0.2–0.3 mm per tip, but that varies by unit — calibrate yours by pouring a measured amount of water through the funnel and counting the tips it produces, rather than trusting a spec sheet.

Feed the resulting "rain in the last period" sensor into ZoneFlow as its rain-gauge input, and the water already received step of every run can deduct real rainfall instead of relying on a forecast alone.

Protecting it from moisture

A rain gauge's whole job is to sit outside and get wet, and a Zigbee sensor board was designed to live indoors on a door frame — not next to a stream of rainwater and condensation. Once the wiring is bridged and tested, brush a thin coat of a clear, moisture-proof RTV silicone over the populated side of the board before you close everything back up. We use Kafuter K-705 (a clear RTV silicone sold specifically for insulating and moisture-proofing electronics), but any similar hobbyist "conformal coating" silicone sold for PCB protection will do the job.

A few things worth doing before you seal it up:

  • Let the silicone cure fully (RTV silicones cure at room temperature over a day or so) before closing the housing — sealing in uncured solvent fumes does more harm than good.
  • Keep it off the battery contacts and away from the antenna trace, so you don't affect the connection you're relying on.
  • Recoat every season or two if you notice the gauge losing connectivity after heavy rain — silicone coatings aren't forever outdoors.

The result

This isn't going to replace a certified weather-station-grade rain gauge, and it's worth double-checking your calibration against a measuring cup before you trust it fully. But for the price of a $10–$15 tipping-bucket mechanism and a sensor you probably already own, it gives ZoneFlow the one input a forecast can't: how much water actually landed in your garden today.