I ordered mine directly from RadioControlli in Italy (I got a few of their RF modules too, they have some really nice good quality stuff).
The physical principle is different. The ‘normal’ ones measure resistance. When rain falls onto the exposed PCB traces, it connects the traces and lowers the overall resistance as rain water conducts electricity. The more rain, the lower the resistance. For that to work, the electrical traces have to be exposed so that the water can touch and ‘short’ them. That will make them degrade easily with dirt and corrosion.
Capacitive sensors work differently. They don’t measure the resistance but the capacitance. The traces are completely insulated in a non conductive resin substrate, forming a capacitor. No water ever gets to them, so they will not degrade. When rain drops fall onto the (insulated) surface, the value of the capacitor changes, because the water acts as a dielectric. This works without direct electric contact. It’s similar to the way touch screens operate. The detection circuit measures the capacitance of the rain sensor. The more rain drops, the higher the capacitance.
Even though they look similar, both aren’t directly interchangeable. They need their own detection circuits, due to the different physical properties measured in each (resistance vs capacitance).
I might have to get them from italy. I see some on eBay but all from China. I did order a tipping bucket rain sensor from Aliexpress to also measure rainfall.
Thanks, very useful info.
Even though they look similar, both aren’t directly interchangeable. They need their own detection circuits, due to the different physical properties measured in each (resistance vs capacitance).
also come with a little sensor, which actually allows for snow/humidity but i expect that needs some more work from me to process the signal software wise. I have to check the pdf that came with it though.
Rain, snow, humidity, it’s all the same to the sensor. It will detect anything that lowers the resistance and/or shorts the tracks on the pcb and you can’t distinguish between them. If you take anything conductive, like a metal screw or nail, aluminium foil or anything like that and put it onto the sensor, it will also detect it as ‘rain’. This is all very very basic stuff.
I guess you can just use the ones you already have and see how it goes.
I found this useful link : Resistive Rain Sensor Products
I use a VELUX rain sensor since many years now and it is very reliable.
I will try the Kemo that seems profesionnal as well.
I tried chinese PCB plates a long time ago and it works 2/3 months before to die. Corrosion, UV, etc … are probably the cause of their death !
That’s an interesting concept. Please post back here when you’ve got some experience.
I’d especially like to know how accurate it is when conditions get beyond just counting drops. For example, you can have a torrential rain where inches of water per hour are coming down, or a steady rain with much less volume. It seems to me that in both cases, the sensor would just stay wet all over. How would it know the volume of water running down the outside of the case?
@CaptTom that is a very good question. Installed on Saturday and only rained today. See chart below. It claims to be accurate within 10% error to “nominal”. I am guessing the optical sensors is not counting droplets on the dome, but the consolidating and moving stream across the dome. There is a separate Hydreon thread on this forum I was going to ask some questions there around what resets the “Rain Event”.
Edit: The mm of rain reported under Rain represents amount within 60 seconds.
Just get a weather station that ties into HA! Even the tempest weather station for example I have heard is not 100% accurate with regards to rain measurement… what about the old true and reliable tipping bucket they have on the all-in one weather styations like the AmbientWeather WS-2902C/D?
Rain tipping buckets are great at measuring rain, but not so much at detecting rain. Because they need a minimum amount of rain to trigger the bucket flip. So if you need something to tell your HA that things are about to get wet outside, a rain bucket alone won’t do.
Very valid point, and if it is a light misting it might even take the bucket a very long time to tip or it might not tip at all! So what exactly is your use case? You have something outside that would be permanently damaged by being hit by the very first raindrops - or you have to act fast to cover it up or bring it inside just before a real rain starts, or -
To be honest, I don’t know. But that’s what the OP asked for
I personally removed the rain detector I installed last year and that I mentioned above. While it worked great, I didn’t really find anything useful to do with the provided data. For me, my rain tipping bucket and a general outdoor temperature/humidity sensor is enough. But I guess there may be other use cases that warrant more fine grained rain detection.
For me it would be mostly curiosity. How much rain did we get last night? Maybe bragging rights if we got a lot of rain. There are practical reasons, like watching the correlation between sump pump run time and amount of rain, or knowing when the garden might need some watering. My old weather station had a tipping sensor, and that worked great for everything I needed, but it couldn’t interface with HA and it finally died in a hail storm.
The other use case would be things like closing windows and such when rain is detected. The tipping sensor would not be so good at that.
I have an AmbientWeather WS-2902C and it just does that with the windows - works very well. For example here is an alert that goes out when it starts raining and the kitchen window is open:
alias: Notify Residents - Started Raining, Kitchen Window Open
description: ""
trigger:
- type: value
platform: device
device_id: 253000e0de69a135d5c86986931d22a7
entity_id: sensor.ridgewood_estate_personal_weather_station_daily_rain
domain: sensor
above: 0
condition:
- condition: state
entity_id: binary_sensor.kitchen_window_state
state: "on"
action:
- service: notify.ridgewood_estate_text_message
data:
title: >-
Ridgewood Estate Automation at {{
now().strftime('%-I:%M%p').replace('AM','am').replace('PM','pm') }}
message: >-
The Kitchen window is open while rain was just detected at
{{as_datetime(states('sensor.ridgewood_estate_personal_weather_station_last_rain')).strftime('%-I:%M%p').replace('AM','am').replace('PM','pm')
}} - close the kitchen window!
mode: parallel
I actually built upon that when the air conditioning or heat goes on or off and the window is open do something similar, and then when it is closed if it is raining to actually thank you (a ittle ridiculous but fun!)
The reason why I put the exact time in there is, these notifications are sent by text message (actually an email sent to @vtext.com for verizon), and soimetimes there is a ridiculous delay before the message is sent - so working on gettting a better (and free) mechanism for same as well…
I have a 6,500 litre rainwater harvesting tank that collects water off the roof; since I have a very accurate depth sensor and I know the area of the roof then I can claim to have the biggest and smallest rain sensors! So far all my sensors are doubled up so no change here.
I am on the coast and run a fairly accurate weather station so this seems a really obvious toy to complete the station. I will run automations off it that will compliment existing Velux and Hunter systems. As well as rain warnings! Will report back
The rain sensor for the WS-2902C works on the old fashioned (but much people say the most reliable) way of a tiny bucket that tilts when it is full, and nearly as soon as it starts raining it tilts. I use that to remind me to close the specific windows that are open, etc.being close to a window for the rain sensor only, in this case, MAY make the rain sensor more accurate as it is less affected by wind - unless the rain is bounding off the window or side of the building and going into the bucket of course. HOWEVER, the WS-2902C (I think there is a WS-2902D now) is an all-in one unit - meaning - the wind direction and wind sensor is on the same unit - and those measurements become compleately useless if the unit is against the side of the building. Ideally you would have the sensors separated, so the temperature sensor would be 5 feet off the ground in an area that is not completely in the sun and not completely in the shade - the anemometer and wind direction sensor should be as high up as possible away from trees - the rain sensor should be somewhere that is somewhat protected by wind to get a true measure, etc. However if you are going to have everything in the very most perfect spot you are talking about alot of expensive equipment going into the thousands and such a tower would be unsightly, etc. So a unit like the WS-2902C or WS-2902D which has verything built in is a slight compromise but that really is no issue. Mine is about 15 feet above my roof (but then that makes it a hassle to service, etc.)
@KruseLuds I agree with that. All my sensors are located in completely different places! Particularly rain sensor (see above) which is protected from wind and some direct low sunlight. I get instant alert of rain; I assumed quicker than tipping bucket
!
