I have written to them. However, I am not sure if the sensor is heated so that it will evaporate the moisture quicker. I think it would need to be heated to give a more accurate reading of when the rain stopped. If it is not heated the water will take a long time to evaporate and it will still be registering rain when there is none.
Chris Jones mentioned that he has one with a heater. I would be interested in a diagram of it when he can post it. I am not sure where he got it or if he made it up.
So do you think these sensors will be able to tell you when there is light drizzle and when it stops?
Many years ago I also heard of a sensor that had some sort of salt or mineral coating so that when it was wet it would conduct electricity better. This could overcome the problem that water has a very high resistance and also make the sensor more accurate. However, a problem could be that the salt or whatever is used may wash off. Do you know any of them like this?
True - I think it's designed to model a leaf more than rainfall as such, although you could retrofit a heater underneath it easily enough.
Again, with a heater possibly, although there may be an error when it stops, as it might take time for the water to evaporate. That said, the unit's output will vary coninuously with the quantity of water on the surface, so as soon as it stops I expect you'd see some change.
This design is *very* sensitive - it responds to clean water.
They do seem to have a painted version, but I don't think this is to improve conductivity. As I mentioned, I've built the circuit for another application (moisture sensing) and it is very sensitive even to clean rainwater.
Sorry Chris. Actually it was Match who wrote the letter. It is just that your name was near the top and quoted so I thought it was yours. Do you know the contact details of Match, or could he email me the information?
There is another kind of senor no one has mentioned, that may be worth considering... VIBRATION / SOUND. If you are only considering droplets moving largely under gravity, then a tallish un-resonant column with a sound-absorbtive inner surface (to reduce wind noise even more) may nicely complement ( a resistive sensor) , or even suffice as a 'drizzle' detector. It could/would work by having a large-surface area thin 'plate' connected directly to either a piezo or speaker-type tranducer. Fed straight into a low-noise high gain audio amp, the output would be super-amplifyed 'pings' of dirzzle landing on the 'rain-microphone'. The problem then of course is decoding this into amount of drizzle. I suggest putting output straight into sound card of PC, simple bit of SW would be able to separate out wind noise from droplet pings, provided some calibration work is done before hand. An active bandpass filter after LNA would be wise too.
In your kind of problem, it may not be a simple matter of "drizzle or not?". One might consider there to be a 2 dimensions of atmospheric water : droplet size, and droplets / volume (density) , where drizzle free, high humidity represents very small droplets, but a high density, and a shower in a dry southern area might be large drops, but low density. I only say this, because it is likely that for good accuracy, it is often better to combine detections of 2 or more sensors (eg radar and resistance) to increase probability of correct output. (EG With resistance detector, How do know the difference between high humidity and drizzle? ..(without also knowing humidity) .)
Another thing that has not been discussed is droplet resonance, where at a particular radio or sound frequency, the absorbtion of energy by the droplet rapidly increases. There should be science literature (esp at BOM) available that discusses droplet size for drizzle, and any decent sound or radar book will have a small section (or refs at least) on radio / sound properties wrt drop-size.
If you are lucky, drizzle droplets will all be roughyly the same size, meaning that a simple ultrasonic path-loss measurment at a narrow band centred on the resonant frequency will reveal drizzle.
Obviously a good topic, with so many responses! Good luck. David Merrett.
We had a cyclone which you should have heard about on the news.
How difficult or expensive could this be to set up? Could one of the options you said be transmitted over a couple of miles to determine if there is any drizzle over that distance?
Your help is appreciated, Regards Richard.
Sim> There is another kind of senor no one has mentioned, that may be worth
Richard, If I were you, I would firstly get some contacts at the BOM, and ask them about this problem. They have probably thought about it before. As a hobbyist, cost is an issue - so whatever you try will be partly driven by your'e expertise with the technology... (the more basic the components, the more work required to develop interfaces.)
I like youre IR tx-rx idea the best, and I doubt you'll find many people around the world who specifically tackled the problem. An IR laser diode focussed to a narrow beam (or even just a laser pointer). , and a di-chroic filter at the same wavelength for the RX (again, focussed) so you dont get drowned out by ambient levels.
Talk to some optical people for this one.... research the technology yourself, and try to copy a similar system (eg..lookup "LIDAR", as used for ocean depth measurements), then perhaps contact physics dept.s or optics / electronics suppliers for the parts. You'll need an amplifier of course, and some basic electronics understanding, or someone willing to volunteer the time to design it for you. David merrett
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