Rain affecting signals and sensing rain.

Hi

I am thinking of making a rain sensor to detect light rain as the BOM radar is often not accurate at measuring light rain in my local area. I have an Internet weather station linked to

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.

I heard some wireless transmissions can be affected greatly by rain so if I set up a transmitter and receiver, the signal would get weaker in the rain and the strength of it could be measured. The distance between the transmitter and receiver could be experimented with. Perhaps I could set up one for the very local area where the distance between the transmitter and receiver is only about 50 or 100 meters. However, another one could be set up so that it spans a distance of a kilometer or more. The signal could extend between my house and someone else's place in the direction where the prevailing weather comes from. This would alert us when rain is about to arrive.

It would be good if the sensor detected even light drizzle. Ideally it would be nice to see or measure the signal reduce as the drizzle or rain became heavier between the transmitter and receiver.

Is there a simple way to do this, such as by using an infa red transmitter and receiver? The receiver could be housed in a pipe to block out as much background interference as possible and so it only received signals from the direction of the transmitter.

Another alternative could be a low cost radar if one is suitable.

What sort of transmitters and receivers could be used and would the setup be affordable? How accurate would the system be?

Your help is appreciated, Regards Richard.

Reply to
richardghole
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You want sensitive, accurate, cheap and simple. Any other options?

Seriously, if you want a simple way to detect rain, Google rain detector circuit. Build a sensor (basically just a mesh of tracks on a circuit board which get a low-resistance path across them when they get wet. Stay away from the RF stuff, it's cheap/accurate/reliable (pick two). Note I don't include simple. The other sort of sensor though is easy - however it will tell you it *is* raining, not that it *will*. Therefore if you have neighbours who are interested also you could set up a network of these in the district and maybe use wireless IP or some such to let each other know what's happening. That'd be a neat community project.

Here's just one page plucked at random from the search result:

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Make the sensor really big with close tracks and it becomes more sensitive to light rain. Note though that you'll probably detect fog too. Plenty of room for experimentation! :-)

Cheers.

Ken

Reply to
Ken Taylor

Hi

Thanks for you suggestion. I have thought of the exact thing that you mention and I was about to get someone to make it up. However, he said that there would be a fair bit of time and electronics involved as the resistance of rain water would be very low and difficult to measure and sense. Also the acidity of rain can vary and this may cause major inaccuracies. Another way I thought of doing it would be by putting two bits of fine mesh very close together but not quiet touching. One would be positive and the other negative. There would be a short when the raindrop bridged the two pieces of mesh. Also a heater would have to be going near the system so it would dry out quickly after the rain stopped so that the system would reset itself for the next lot of rain.

One way I thought of that may make the electronics simpler would be to use very high voltage like on the bug zappers. This may make changes in voltage or current larger and this may be more easily be able to be measured. I am not sure what you think would be the best way to go if I make up something like this.

However, even if I make the above up I would still like to be able to try something like a lazar over a distance of about one kilometre to measure rain that is approaching. I think this could be simpler than the other suggestion of a network of sensors via the Internet. The lazar would be pointed at a light dependent resister. The light dependent resister would be housed in a tube to stop as much other light entering as possible. When there is rain or drizzle around, it would partially dim the light from the lazar so that the light dependent resister would put out a lower voltage.

Another type of lazar or diode may be better than a light lazar. For example an infa-red diode which could use resisters that respond to infa-red instead. This may make it more accurate in the day time as outside light may affect it less. I also thought other types of radiation could be used such as micro waves etc.

What do you think would be the easiest way to go based on the above suggestions?

Your help is appreciated Regards Richard.

Reply to
richardghole

How much electronics experience do you have?

I think the what the BOM use is probably the best solution. RADAR.

Laser doppler (as with any optical system) is no good in fog/polution. PCB based sensors have poor response time, and when the rains stops you need to wait for the water to evaporate. High volatage is susceptable to moisture and high humidity.

Reply to
The Real Andy

Hi

How much would radar cost? I think it would be very expensive?

We do not get a lot of pollution or fog in our area that obscures visibility, so lazar may work ok. However, it would be a bit of trouble to line everything up over a long distance.

I thought there may be some other signal that would also work which would be easier to line up as they would have a wider beam and would be less affected by outside radiation . However, I understand no matter what I would use I would need line of sight

If anyone has any more ideas on this and what I stated in the previous letter, please let me know.

I do not have a lot of electronics experience, but I know someone who can help.

Your help is appreciated, Regards Richard.

Reply to
richardghole

Note: it helps to include at least some of the post you are replying to so we have some context for the discussion.

Yes, the radar will cost a lot more than the other simple methods here. Also, you are unlikely to get it licenced. Or calibrated. The BoM has pretty strict procedures for cal'ing radar (and everything else) so that they get meaningful results. I also would hesitate to suggest you use one when they are actually dangerous when used incorrectly.

A laser or similar beam is susceptible to being interrupted by animals, birds, people, etc. Can you reliably get around that problem? Also note that a laser powerful enough to go the distances you are talking about is likely to be a hazard to eyeballs.

I didn't bother to take you to task earlier on your statement that their radar is unreliable in your area - what do you mean by this? Are you outside the area(s) of coverage, or you just feel the radar is unreliable?

Have you considered checking out the satellite coverage? Also available at BoM's site - not as real-time as the radar though. The reason you are not seeing the very light drizzle you want is that it is essentially insignificant so gets averaged out. Do you really care about precipitation in such small quantities?

Not trying to tell you how to suck eggs or anything but the simple detector with a large fine mesh should work well enough. A high voltage won't be of significant use though it may kill the moths. :-)

Cheers.

Ken

Reply to
Ken Taylor

You know the noise that rain makes on a tin roof? Well my suggestion is to get a tin can or plastic sheet and attach the element of a piezo buzzer to the inside surface of the end of it or use a moving coil speaker with a high gain amplifier, and then design some kind of filter (probably high pass) that feeds a comparator that will trigger off the sound of a rain drop hitting the diaphragm but not from ordinary noises.

If you can get the signal processing right then it should be very cheap and the sensitivity could be improved by adding more of them and totalling the number of pulses per minute.

Chris

Reply to
Chris Jones

Unreliable readings from the rain radars are quite common - there's an explanation on the BOM site explaining this. The most common issue is the curvature of the earth and the multiple beam angles used to try and achieve a consistent sensing altitude across the scan radius, which I think is something like 3,000 feet. If rain is forming below this it won't be seen.

Reply to
Poxy

Hi

Thanks for the letters.

We get a lot of drizzle in our area which does not get detected by radar or audiably by sound on a roof. Also the radar covers a large area and does not detect small amounts of rain. The frames are also only updated every 10 minutes. However, the drizzle we get is still enough to wet things. I am on the Atherton Tableland at 737 meters altitude.

So is there any other signals or radiation apart from lazar light that would have their strength reduced by such precipitation so that their strength could be easily measured?

Your help is appreciated, Regards Richard.

Reply to
richardghole

The problem with using path loss to detect rain is that other things will cause path loss as well. It won't be any more dependable than the radar. Again, why not try out the simple sensor?

Cheers.

Ken

Reply to
Ken Taylor

A piece of Veroboard mounted on a steep angle (so most of the rain runs straight off) might be an easy way to prototype a simple sensor. Just connect all the odd tracks together, and then all the even tracks together, and (depending on the requirements of the OP), check for continuity or measure the resistance between the pairs of tracks.

I believe Jaycar and Altronics carry Veroboard. I doubt it'd be suitable for long-term outdoor use, but it'd be hard to beat for a "proof of concept".

Peter

Reply to
Pete

How about a large collector (think *big* funnel, or possibly even the existing roof drainage system) and in the output pipe, either a flow sensor (to give a range of outputs depending on actual rainfall), or a simple continuity test to detect rain/no rain.

Rethinks: perhaps the "dynamic range" of the existing guttering and downpipes might be just a *little* too large between "barely raining" and "extreme storm" :-)

Peter

Reply to
Pete

As others have said, the problem is that pretty much anything in the air (dust, pollen, haze, smoke) is going to attenuate a beam.

My suggestion is to try the circuit at the bottom of this page:

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It's a simple circuit - you can just use a standard 555 and regulator rather than the specialised versions they use, it is hella-sensitive, the sensor is a simple grid - you could use veroboard as someone suggested, or maybe make up something finer, and you can interface the output a number of ways, voltage, current or frequency - the latter being a very easy way to interface to a micro.

Reply to
Poxy

If you use too big a collector, light rain (an undefined variable) may evaporate before getting tot he sensor. But in principle a good idea.

Cheers.

Ken

Reply to
Ken Taylor

Hi

Thanks for your letter.

I plan to get some Veroboard. However, stainless steel mesh would last longer and may be easier to mount with a very small gap between the two pieces of mesh. Or do you think fine mesh could have other disadvantages? I am thinking of using some with holes of about 2mm across.

The rain I want to detect would often be before there is any runoff so the idea about the funnel is no good. I have a tipping bucket rain gauge that measures the intensity of heavier rain and it is graphed out at

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I would still like to try a signal as well as it would not matter if other things interrupted it on occasions. It would still give an idea and would be able to detect lighter rain than the radar. If you know of any other radiation that would be better than light to use, please let me know.

Your help is appreciated, Regards Richard.

Reply to
richardghole

just measure relative humidty,

if it's 100% there's excess moisture in the air. (sleet/hail/rain/drizzle/fog)

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   Jasen
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Reply to
Jasen Betts

The radar is most likely able to detect the rain. There is one proviso though, it has to be able to see it from it's point of view.

The lowest threshold is actually a fair bit higher than light drizzle. It is also possible that the radar is detecting it, but the signal is being suppressed. The level 1 threshold of 12dBz is roughly equivalent to 0.2mm/hour.

Which radar are you using? Cairns?

If it is light drizzle on the hills, it is also possible that the radar is gating the signal off due to massive permanent echo contamination.

Cheers, Ray

Reply to
Ray

I will post an image of my data, but I'm using a leaf wetness sensor with a heater and it works

Match

Reply to
Match

Hi

Thanks for your letter.

I would be interested in getting a leaf wetness sensor made. However, I do not have much electronics experience or time. Could you or do you know of anyone who could make one up for me or are there any made up units for sale. If so, how much would it cost to either buy one or get one made? How long do they take to make? I am about to make an order from Electus Distribution so I could purchase the parts.

I have a data logger that collects data so that the weather can be graphed out. It is then automatically uploaded on to a public site linked to

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The logger requires between 0 and 5 volts. The voltage values are saved in a text file and pasted into Microsoft Excel to be converted into the values I need and graphed out. It would be good if very light drizzle registered at perhaps the lowest voltage and heavier drizzle was logged at a higher voltage so that a graph could be created. Also it would be good to put an alarm on the wetness sensor so it would buzz even when light drizzle is falling on it. The buzzer could be switched off and separate to the computer and data logger.

Could you also please contact me by email if possible. The address is snipped-for-privacy@truesolutions.info or you can go to the website above.

Your help is appreciated, Regards Richard.

Reply to
richardghole

I'm not sure whose you are replying to, but the leaf wetness sensor on this page

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is available from them for US$65 It's listed about 3/4 down on this page:
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The base unit puts out 0.2-1v but it looks like you can get one with a more suitable voltage output for an extra $10. I'd suggest you send them an email if you're interested.

Reply to
Poxy

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