[hvalentim]

A ultrasonic wind gauge for ~99 Euros or less (Amazon sells them for 79 USD) seems very appealing.

Unfortunately Netatmo adopted a closed cloud based architecture that does not make it very easy to hack. And transmissions are in the 868Mhz band.

Some progress was made as to decode the transmissions from the base station, but I have not found anything on decoding a single sensor...

Anyone knowledgeable enough to try?

Spec.s:

4 ultrasonic transducers
Wind speed: Range: 0 to 45 m/s (160 km/h, 100 mph)
Accuracy: 0.5 m/s (1.8 km/h, 1 mph)
Wind direction: Accuracy: 5°

[AllyCat]

Hi,

Hmm, that's rather interesting. This link suggests that it "Works with" various "open" products, but I wonder if it is directly at the 868/915 MHz frequency, or only via WiFi (i.e. the Netatmo hub).

Several of those "compatible" devices appear to support Zigbee (which can operate at 868, 915 MHz and 2.4GHz), but others appear to be only 2.4GHz (WiFi / Bluetooth, etc.). So I take that "compatibility" diagram with a large pinch of salt.

To "hack" the wireless protocol, you really need to know what is being transmitted which implies you also need to buy a receiver/hub. Even then the data may not be directly accessible but only via a Web Browser / The Cloud. So sorry, I'm not volunteering at the moment. I note that one of their FAQs is
"Q11: Does the Netatmo Weather Station have a Windows / Desktop / PC App?
No, unfortunately the Netatmo Weather Station has no Windows / Desktop / PC App at the moment".

On a more general note of "usefulness"; the wind sensor is described as "battery operated" and doesn't appear to have solar charging. That means the "power budget" would be very limited, which can be achieved (only) by measuring and transmitting data rather infrequently. In a review, there was a comment that the data only "updates" once every five minutes, which might not be sufficient for a "real" weather station.

Cheers, Alan.

PS: The (FAQ) "Answers" on the page linked above, from Q17 to Q32 imply that it doesn't use any "known" wireless protocol. And Q33 confirms that it uses (only) 4 x AA cells to give "up to" one year of use.

[hvalentim]

Thanks a lot for your comments Alan. They were very helpful.

You do have a point. "4 AA batteries (up to 2 years autonomy)" should mean it only transmits (averaged?) data once in a while (perhaps the 5 min.s in the review you mention). Still, it could be an option, considering storing 5 minutes averaged values is what most of us are doing currently.

As far as I understand per design ALL data must go through their web-servers and only afterwards is made available through an API (you can "freely" access it from there).

So, the hardware effectively seems to be as closed as it can be. To the point of sheer nonsense.

Extra sensors communicate with the base station using 868Mhz (it's in the spec.s in their website somewhere), and data is sent by IP to their servers (the link I place in my previous post pertains the hacking/interception of the packets sent by the base unit via Wi-Fi). The thing is: do they somehow obfuscate data sent by sensors to the base unit (I mean, does some sort of per case "handshake"/encryption key exchange occur between the main unit and a sensor)? If not, data sent per optional sensor could theoretically be decipherable without owning a base unit.

[AllyCat]

Hi,

Modern "intelligent" radio chips are so sophisticated (but cheap) with capabilities for data bufferering, FSK, channel hopping and even spread spectrum, etc. that the transmiisions may be very difficult to "hack", even if the designer didn't intentionally aim to encrypt the transmissions. So I don't think I'd try, even if the Netatmo were a "useful" Wind Gauge.

But IMHO a modular (wireless linked) wind gauge which needs 4 AA cells to be changed every year is not a "serious" sensor. Even the Fine Offset stations have a few metres of cable to their wind sensors, so the "battery box" (transmitter) can be more conveniently located, and it needs only two AA cellls to be replaced every few years. Also, the "active" (ultrasonic transmission) method must consume much more power than a simple "counter", so I don't see how it could detect wind gusts, but must just take a "snapshot" every few (five ?) minutes. For a wind sensor like the Netatmo, solar recharging seems the "obvious" choice.

However, the "ultrasonic time of flight" is an excellent method for measuring wind speed/direction and is not too difficult for a hobbyist to implement, using a microcontroller. So a "tear down" of the Metatmo might be rather interesting, but you'd likely end up with some knowledge, but a non-functioning sensor.

I did actually develop a microcontroller-based ultrasonic time of flight air speed (not direction) sensor about 30 years ago. Now, very low cost ultrasonic "rangefinders" are available for "Arduinos", but I don't know if they would be sufficiently weatherproof (or accurate). So I would probably start with the type of ultrasonic transducer used in automobile reversing sensors.

Normally, the "flight path" would be some tens of cms to give an adequate delay/variation, but an alernative method (which I used) is to compare the phase of the received to transmitted signal (which can be done easily with a flip-flop, low pass filter and an ADC). Basically, three "universal" transducers (i.e. able to transmit or receive) on an equilateral triangle could produce six path measurements (including "forwards" and "backwards") to enable calculation of two airspeed vectors (at right angles) and eliminate variations of the speed of sound (due to temperature and humidity, etc.).

Maybe something I'll try eventually, but I really want to get my sunshine sensor project "finished" first.

Cheers, Alan.