Rain sensor not prone to corossion?

Hi all,

I have tried using the standard resistive rain/water sensor (bought from ebay) to detect rain. The sensor /arduino controller triggers a controller which closes an awning when rain is detected.

Unfortunately, the sensor corrodes after a few days and it becomes unresponsive.

Anyone has any ideas for alternatives or how to overcome this problem?

Check out the ones used on cars for automatic wipers. IIRC it's an optical affair with a sensor looking at a lens/mirror.

What's IIRC?

I got around this years ago, by converting the resistive sensor into a capacitive one. I sprayed a very thin layer of conformal coating onto the entire surface of the sensor. This not only waterproofed the sensor, it also became a capacitive sensor. You then need to ditch the module board that came with it, and connect/power the sensor with an AC circuit, basically using your arduino IO to reverse the polarity every time you take a reading.

Or perhaps you can just get a capacitive soil sensor on ebay. It really doesn't make a good soil moisture sensor, but I think it will work nicely for a rain sensor after waterproofing the portion of exposed electrical components.

Watcher: What's IIRC?

If I Remember Correctly.

If I Recall Correctly.

Yes, the car ones are optical.

You can use those cheap sensors a lot longer if you power them down between readings. Every 5 mins a reading is enough. Use three pins: set to output (high for power, low for gnd) when measuring, set to input when done. Such sensors shouldn't take more than a few mA so that's OK to power off a pin.

I like the idea of a car optical sensor but the question is where to get one and how to use it...there are lots on ebay but there is no documentation

Watcher: I like the idea of a car optical sensor but the question is where to get one and how to use it

Find some models which have that feature and visit your local junkyard.

And then extract the entire windscreen from the junkyard? I'm sure the automotive sensors are exquisitely tuned for the exact thickness of windscreen in front of them.

MorganS: And then extract the entire windscreen from the junkyard? I'm sure the automotive sensors are exquisitely tuned for the exact thickness of windscreen in front of them.

Yea..my thoughts exactly. .

Surely there must be a more ..feasible solution to a this usual (must be) problem...

Surely there must be a more ..feasible solution to a this usual (must be) problem...

Use low voltage AC with resistive sensors to prevent electrolysis, and use stainless steel sensor electrodes - that will last far better.

MarkT: Use low voltage AC with resistive sensors to prevent electrolysis, and use stainless steel sensor electrodes - that will last far better.

Then none of the ready made resistive sensors will do...

TRW's version

Why not use a “tipping bucket “ type sensor ? ( google)

There is stuff on the net on how the car ones work - worth a Punt on eBay ? You might be able to use the optics if nothing else ?

As already mentioned ..You might be able to make a better resistive one from say platinum wire , only power occasionally , maybe drive it through a H bridge arrangement to periodically reverse the voltage on it ? ( you don’t need to measure resistance on neg cycle maybe ( needs thinking about ))

Capacitive rain(drop) sensors should be added to the list of Arduino sensors. Leo..

Reversing voltage should not be necessary if you power it just for 1 ms every minute or so. That's enough to measure whether there's water, doesn't cause any significant corrosion (the normal exposure will do more).

Reversing voltages matters if you want to do accurate measurements of the resistance like in EC measurements. Here you don't care about accuracy.

Wawa: Capacitive rain(drop) sensors should be added to the list of Arduino sensors.

That is a very neat sensor - simple, inexpensive, and no doubt effective (water drops on the surface will indeed change the capacitance big time). It's just not too easy to read, it'll at least need a large resistor so the discharge time can be measured in software. Or a 220-330p capacitor in series; charge both to Vcc, then connect the one end to GND and measure the voltage at the mid point. Very low power consumption, great for battery operation.

I just don't see the use of the heater (to evaporate the rain faster??) and what they want with that thermistor. Those are not good for battery operation.

There are three separate/independent circuits on that sensor (six contacts). The thermistor, to measure/control sensor temperature, and the heater are ofcourse optional. But the heater might occasionally be needed to remove morning dew (which is not rain) of moisture from fog, or to get the sensor faster ready for new rain drops. Leo..

Thanks Leo for the info.

Couldnt find one on ebay so ordered a capactive soil sensor instead to try as a rain detector . I ll give it a try when it arrives...