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High-precision rain gauge using Pro Mini, Piezo, Diff Amp, B
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Please be positive and constructive with your questions and comments.

High-precision rain gauge using Pro Mini, Piezo, Diff Amp, B

by Govner on Tue Sep 24, 2019 1:55 am

Completed_piezo_rainGuage.jpg
Solar panel is part of the wireless system
Completed_piezo_rainGuage.jpg (123.15 KiB) Viewed 477 times
I have never been happy with the resolution or operation of "rocker-type" rain gauges. Moving parts and constricted water entry openings are enevitable sources of problems. Why not have a no-moving-parts, water-proof detector. "Waterproof" ? How can that be? Enter stage left, a piezo crystal detection unit.

This unit is capable of counting rain drops at a rate (about 2 usec between drops, est.) that far exceeds the world's record rainfall rate (Google: South America 1.5-inches/minute). In any case, my goal was not worrying about the fact that research assigns 1 uL/drop or some such thing. I just wanted to get the big picture so I could inhibit irrigation pumps when enough rain warranted that. And with a simple evaporation algorithm, re-enable the pumps. All control had to be wireless so I just added another NRF24L01+ 2.4Ghz transceiver ($2 USD) to my existing network. Piece of cake. I used a glass MASON jar which is used for preserving foodstuffs and is completely waterproof. I used a glass one (as you can see) but plastic would have been easier for drilling the small hole in the bottom for DC power. I used a diamond drill bit and it took all of about 30 seconds. No biggie.

Happy to share anything/everything done on this project. I used Pro Mini, 4 piezo elements, differential amplifier, Buck power supply (I like the buffering between my solar panel system), BME280, NRF24L01, DS3231 RTC.

I just wire-wrapped the assembly on a PCB that I designed for general purposes like this. I recommend using electrical contact grease around the lip of the glass jar just to get a great, lasting seal. (That's another reason why I chose not to use plastic. Glass has a far superior long-term reliability in this regard).

The unit works far better than I expected and has other applications. The processing speed is so nice that, when I did the "shower stall test", I could increase the droplet rate and see the drop-to-drop LED response. At the maximum rate, the LED just can't keep up with the rate and appears to be lit steady.


Completed_piezo_rainGuage.jpg
Solar panel is part of the wireless system
Completed_piezo_rainGuage.jpg (123.15 KiB) Viewed 477 times
Attachments
Completed_PiezoRainGuage_nSolar.JPG
Close up of piezo-based rain drop measurement unit
Completed_PiezoRainGuage_nSolar.JPG (121.95 KiB) Viewed 474 times

Govner
 
Posts: 175
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Re: High-precision rain gauge using Pro Mini, Piezo, Diff Am

by adafruit_support_bill on Tue Sep 24, 2019 5:47 am

Nice project! Thanks for posting.

adafruit_support_bill
 
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Re: High-precision rain gauge using Pro Mini, Piezo, Diff Am

by millercommamatt on Tue Sep 24, 2019 8:17 am

Neat. This looks like a DIY Yost impact disdrometer. With some creative signal processing, you should be able to handle simultaneous droplet impact and sort out droplet size.

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Re: High-precision rain gauge using Pro Mini, Piezo, Diff Am

by Govner on Wed Sep 25, 2019 10:06 pm

For those wishing to build your own, here's a schematic that I tossed together for that purpose. If there are questions, feel free to fire away.

I would encourage anyone interested to try it. It will not disappoint. I have one installed on my patio, battery powered, solar charged, and is transmitting to my inside unit 24/7. Bird droppings notwithstanding, the sensor tests 100% reliable in detecting rain drops at most all possible rain densities/intensities. Simultaneous droplet impacts less than 10 usec apart or so will be counted at one impact. There is no "contact bounce" so all impacts are well-defined square-wave inputs to the Pro-Mini. Enjoy.

Regards,
GOV


Rain_Piezo_RF24_Network.pdf
Schematic diagram of Piezo Rain Detector Design. Author : W.J.Glenn, Released into public domain.
(16.75 KiB) Downloaded 150 times

Govner
 
Posts: 175
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Re: High-precision rain gauge using Pro Mini, Piezo, Diff Am

by millercommamatt on Thu Sep 26, 2019 12:08 am

Impact disdrometers have an issue where the splash from impacting droplets produce a false positive. The typical remedy is to ignore low magnitude impact for a short period of time after a large droplet impact. Have you noticed splash signals with your instrument? Do you know your minimum size sensitivity?

millercommamatt
 
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Re: High-precision rain gauge using Pro Mini, Piezo, Diff Am

by Govner on Thu Sep 26, 2019 5:31 am

millercommamatt wrote:Impact disdrometers have an issue where the splash from impacting droplets produce a false positive. The typical remedy is to ignore low magnitude impact for a short period of time after a large droplet impact. Have you noticed splash signals with your instrument? Do you know your minimum size sensitivity?



For my purposes, these issues involving high-precision measurements are not particularly relavant. But, that's not to say others might have a need and I can see that it would be a fun little research project using this instrument. Innovation is a beautiful thing. Thanks for asking. Regards.

Govner
 
Posts: 175
Joined: Wed Sep 14, 2016 4:42 pm

Please be positive and constructive with your questions and comments.