Arduino Rain Sensor

[Graeme]

The weather has been too wet to be out working on my observatory build so I've been working on my Arduino rain sensor instead! I saw a thread by tosjduenfs on Cloudy Nights which uses an RG-11 rain sensor. But it occurred to me that if you put the sensitivity settings dip switch for sensitivity adjustment on the same circuit board as the Arduino then you could just use a piece of vero strip board as the sensor. Tosjduenfs has written the Arduino sketch and the Safety Monitor Ascom Driver and made it available for all to share. So I have rewritten the code to include sensitivity calculations. A control wire from the sensor is read by an Arduino analogue input. The original code looks for a change of state on D2 and when it sees that it tells the Ascom driver to change from Safe to Not Safe. I use NINA for Astrophotography, the NINA advanced sequencer can use the Safety Monitor to send notifications to a mobile phone, so I have installed Pushover to do this. I've not used it in anger yet because I haven't finished my observatory! But when I do, the plan is, if it rains, I get a notification on my phone and it wakes me up so I can park the telescope and close the roof. This can be automated too, but that's the next step!

When the code has been tidied up I will post a copy here if anyone would like to have a look and comment and point out any school boy errors.

This is the schematic:

 

 

The sensor plate will need a small heater to stop condensation forming and giving false readings.

Regards

Graeme

 

 

 

 

[Tomatobro]

I tried this a while ago and the problem I had was the change is resistance on the stripboard sensor due to oxidation of the copper strips.  

[Graeme]

1 hour ago, Tomatobro said:

I tried this a while ago and the problem I had was the change is resistance on the stripboard sensor due to oxidation of the copper strips.  

 

Hello Tomatobro

Yes, I did wonder how long the copper would last before it started to oxidise and what level of oxidisation it would have to reach before a rain drop fails to allow a change of voltage between the copper strips. A regular wipe with a gentle non abrasive acid like vinegar (or tomato sauce!) would keep it clean. The other problem would be deterioration of the board under the copper strips due to exposure. The MkII version will need to have Nickel-Chromium heating wire under it. 

Either way, Vero board is quite cheap on Ebay and if you're handy with a soldering iron a new sensor plate can be knocked up with ease.

Thanks for the feedback. Did your sensor effectively operate the Safety Monitor before the copper strips became corroded? And how long did it take before that happened?

Graeme

 

[Tomatobro]

given the high cost of the equipment we were trying to protect we went in the end for the Hydreon RG-9 Rain Sensor. These have been running for several years now and are 100 % reliable. They seem to have come down quite a bit in price compared with what we paid back then. 

 

 

[Graeme]

That's a fair point. My situation is that I have been controlling the equipment from indoors for a couple of years now so I'm close to where it's operating. For most of the session I'm monitoring what's happening. But now, with my observatory build I'm hoping to get a lot more all night sessions and there's a good chance of me falling asleep on the settee! I think the Arduino control and the NINA notification are as reliable as any system and although the sensor would be a weak link if not properly maintained, it is easy to keep clean and easily replaceable. 

[EarthLife]

The way it's normally done on say a car is to use an IR LED and monitor the reflected/refracted light in the window screens glass, if it changes then you have water on the outside of the glass (due to blobs of water changing the reflection/refraction direction). It's very simple and reliable.

https://cecas.clemson.edu/cvel/auto/sensors/rain-sensor.html

But to stop copper from corroding just coat it with something like conformal PCB coating or pot it in silicon sealant (local DIY store) etc ?

[skybadger]

You can move from resistance to capacitance measurement using an AC signal , water will change the capacitance. The AC current reduces corrosion.

[Graeme]

12 hours ago, EarthLife said:

The way it's normally done on say a car is to use an IR LED and monitor the reflected/refracted light in the window screens glass, if it changes then you have water on the outside of the glass (due to blobs of water changing the reflection/refraction direction). It's very simple and reliable.

https://cecas.clemson.edu/cvel/auto/sensors/rain-sensor.html

But to stop copper from corroding just coat it with something like conformal PCB coating or pot it in silicon sealant (local DIY store) etc ?

 

Thanks for that. I'll have a read of the information in the link and see if I can improve the sensor to a refractive type. But I can't coat the strip board with an insulating material because it won't change it's resistance when it gets wet.

 

11 hours ago, skybadger said:

You can move from resistance to capacitance measurement using an AC signal , water will change the capacitance. The AC current reduces corrosion.

 

And thanks for that too. Again, I'll have a read up. We use sacrificial earth electrodes on the railway because of the stray dc currents. They get very corroded!

Graeme

 

[Graeme]

So here's a link to a zip file containing the the code, schematic and Ascom driver etc. The text file lists the files included..

https://drive.google.com/file/d/1pdDf8cYwVrWxIS_OOSnR1XC3yR_tG6TO/view?usp=sharing

Graeme

 

Edited April 18, 2023 by Graeme

[kbrown]

I've been meaning to do some experiments with one of these I have in my random electronic components box: https://www.onsemi.com/pdf/datasheet/qrd1114-d.pdf

They don't cost much but would require supporting electronics and a well designed enclosure. One of these days I'll get to it

[Graeme]

51 minutes ago, kbrown said:

I've been meaning to do some experiments with one of these I have in my random electronic components box: https://www.onsemi.com/pdf/datasheet/qrd1114-d.pdf

They don't cost much but would require supporting electronics and a well designed enclosure. One of these days I'll get to it

Thanks, this could be a way forward!

Graeme