ESP8266 Community Forum

- Sun Jun 18, 2017 3:13 pm #67323 I tried the rain experiment for you, but it didn't detect a shower of water drops... presumably not a large enough body of water to cause sufficient doppler-shift reflection.

Bear in mind that it doesn't detect anything absolutely (ie: a stationary train would not trigger it), it merely detects the slight relative difference in doppler effect caused by a radar-reflective moving body.

So in theory if you moved slowly enough you might even be able to defeat it, but in practice I doubt you could traverse it's entire 'field of vision' so imperceptively slowly, especially as it can sense movement from any direction - front, back, over, under, side edge, end edge... I haven't had opportunity to do relative directional sensitivity tests yet, but it doesn't appear to have any actual blind spots, and is remarkably all-around aware.

I have a unit running on my desk I'm developing a program on, and I've noticed it sometimes triggers just from chest movements of breathing, and I've even amused myself by trying to lift a finger without it noticing, but unless done very slowly it detects it every time.

Where to get modules?

https://www.banggood.com/custlink/KvGGhGF4wG

- Sun Jun 18, 2017 4:28 pm #67326

I tried the rain experiment for you, but it didn't detect a shower of water drops... presumably not a large enough body of water to cause sufficient doppler-shift reflection.

Thanks a million! Too bad it did not detect the water. Would have been an excellent use of this module.

Bear in mind that it doesn't detect anything absolutely (ie: a stationary train would not trigger it), it merely detects the slight relative difference in doppler effect caused by a radar-reflective moving body.

So in theory if you moved slowly enough you might even be able to defeat it, but in practice I doubt you could traverse it's entire 'field of vision' so imperceptively slowly, especially as it can sense movement from any direction - front, back, over, under, side edge, end edge... I haven't had opportunity to do relative directional sensitivity tests yet, but it doesn't appear to have any actual blind spots, and is remarkably all-around aware.

I did quite some reading on the modules, and I was aware it reacts to changing reflection.

I figured the falling of raindrops would qualify as "a moving body", and the detector would report "rain" as long as new drops would be detected. When no more waterdrops would fall, the detector would return to the default mode indicating "no, no rain!"

I guess the short distance of waterdrops and sensor and the small mass of the waterdrops does not suffice to provide adequate feedback to the sensor.

I have a unit running on my desk I'm developing a program on, and I've noticed it sometimes triggers just from chest movements of breathing, and I've even amused myself by trying to lift a finger without it noticing, but unless done very slowly it detects it every time.

So it is VERY sensitive at more distance. Maybe it would function as a hurricane detector

Thanks for the experiment and your thoughts. I will certainly continue to follow this thread for further developments, maybe another application will popup to justify the $1 investment

- Mon Jun 19, 2017 8:53 am #67345 The sensor measures velocity relative to itself. An object moving on a circle centered on the detector as no velocity toward the detector so no Doppler effect. Next the signal has a wavelength and rain drops are often dispersed and any rain drop is small relative to wavelength so minimal reflection is expected...direction is also important rain is more vertical than horizontal.

- Mon Jun 19, 2017 12:04 pm #67354

The sensor measures velocity relative to itself. An object moving on a circle centered on the detector as no velocity toward the detector so no Doppler effect. Next the signal has a wavelength and rain drops are often dispersed and any rain drop is small relative to wavelength so minimal reflection is expected...direction is also important rain is more vertical than horizontal.

Interesting!

Yes, "rain is more vertical than horizontal", but I imagine than could have been solved by mounting the sensor horizontally.

And ..... when the sensor can detect a dog/cat a few meters away, detecting a raindrop is "in theory" no different, provided the sensor would have "unlimited" sensitivity.

I can accept that due to "any rain drop is small relative to wavelength so minimal reflection" the drop is not detected. Too bad!

Thx

Off topic : Found an affordable rain sensor that can count "individual raindrops" using reflection of infrared light here:
http://rainsensors.com