Turn an Aqara Water Leak Sensor into an instant rain meter
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In this guide, I will be showing you how to convert a readily available Aqara Water Leak Sensor into an instant rain meter. This project requires no soldering and only a few jumper wires and a rain sensor board to be completed. There is no complicated setup and, as long as you are already using Zigbee and have a hub set up, it will be integrated with Home Assistant instantly.
I've long been a big fan of Aqara Zigbee products. They look good, don't cost much, and are generally pretty accurate. There exactly the type of no-nonsense smart home products I like. Additionally, as this project shows, they can be easily modified for to fulfil a different function than they're intended for.
This project utilizes a rain sensor, which has a series of exposed traces on one side. These traces are not connected, but are near enough to each other to be bridged by raindrops. Thus, the first drop of rain will immediately close the circuit, changing the binary status of the Aqara Water Leak Sensor.
How to attach a rain sensor to an Aqara Water Leak Sensor
The fact that the Aqara Water Leak Sensor has two probes on its underside, to which you can attach any binary sensor, makes this project a lot easier. There is absolutely no soldering involved. All you need is a hex screwdriver to loosen the probes.
Most rain sensors will come with a daughterboard, which will turn the digital signal (on/off) in to an analogue signal, which can report the exact impedance back to the controller. This project only uses the rain sensor, so it will only report whether it is raining or not, and not how much water is on the board.
The rain sensor will have two pins on one of its sides, which you can easily attach to the probes using two jumper wires. To make things a bit more secure, I would use some hot glue to attach the wire to the sensor more permanently.
Where to place the rain meter
As the Aqara Water Leak Sensor is IP67-rated, it should survive in a body of water up to a meter deep for half an hour. For you, that means that you needn't be too picky about where to place your newly constructed rain meter.
There are also numerous 3D prints available for exactly this project. Just make sure you buy a rain sensor that fits the slot, or you will have to manually adjust the model.
Possible issues with the Aqara rain meter
Depending on where you live, the nighttime humidity might be enough to trigger the sensor, as the creator of this 3D model found out. But as you're unlikely to need a rain meter during the night, you might be able to live with it.
Another issue is that the rain sensor isn't heated as it would be on many commercially available products. While your sensor will immediately react to rain, it might take some time for it to be able to report that it isn't raining any more.
Finally, a shoddily constructed rain meter will degrade over time. The traces might rust, or the jumper wires come loose. If you do want to extend the lifetime of your rain meter, makes sure you give it proper protection by placing everything that doesn't need to be exposed into a chassis.