Time for a new weather station?

svetz said:

Could the noise really be so bad they'd need 213 mV at the receiver? After all, AM/FM is in the μV; if your using an amplifier that just seems crazy... is this what happens when you put 7 EEs in a room? I need to re-read that several more times....

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Maybe. Maybe also for convenience; when you don't want to have amps and filters and take the time to tweak all that perfectly right to get your signal out of the noise you just improve the SNR right at the transmitter

Wow, can't really compare that to radio/TV signals, that's a whole another can of worms with some black magic in it... ^^

svetz said:

Didn't mean to imply you were old, and I do understand what you mean... beauty is in the eye of the beholder and and the artistry of something tangible is far more evident then something intangible like s/w (which far to often isn't very pretty at all).

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Yea don't worry, it was just that I wrote it in an ambiguous way so I thought it was a good idea to be more clear

svetz said:

They're using the STM32F429 180 MHz chip, so that's 6 ns/cycle and should be fast enough for 1 mph wind speeds deltas.

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Be careful about using the base clock for that kind of things, sometimes you can have big surprises.

svetz said:

R5 and C3 allow discharging the energy stored in the transducer.

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I'd say it's more a resonant circuit than anything else. You can omit them at the cost of the efficiency.

svetz said:

Then there's D2 is a zener diode and it causes the voltage induced by the primary of the transformer during its unloading to be 13 V? They say:

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Yep, remember the old ignition coils with the mechanical contacts? they used a capacitor to avoid pitting them too fast, here they use a zener to avoid destroying the driver and/or MCU instantly ^^

svetz said:

Sounds suspiciously like magnetic magic, I get the transformer's magnetic field will resist the change in current flow but not how the zener is bumping the voltage up in combination with it. Tried simulating it (see attachment) but didn't see 13V... to many unknowns. Certainly the output transformer voltage didn't ramp up very fast.

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It doesn't bump up the voltage, it's the opposite, it limits it. It's the same thing as why we put a diode in anti-parallel on a relay coil when it's driven by some electronics

BiduleOhm said:

... Yea don't worry...

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I just don't want to offend my sensei as I struggle towards circuit nirvana ;-)

BiduleOhm said:

...It doesn't bump up the voltage, it's the opposite, it limits it. It's the same thing as why we put a diode in anti-parallel on a relay coil when it's driven by some electronics

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I was just questioning what the 7 EEs said:

...component D2 is a zener diode and causes the voltage induced by the primary of the transformer during its unloading to be 13 V.

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According to them it's very important as it gives an 8% signal boost.

Although that's not what I saw when I tried to simulate it; but I'll look at it again soon and see if I can figure it out. They've got a separate driver to protect the MCU. I can't help but wonder if they didn't throw in this as a crazy bit just to see if anyone was reading it.

svetz said:

According to them it's very important as it gives an 8% signal boost.

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That makes sense as you keep the current flowing with D2 (current stored as the magnetic field).

svetz said:

Although that's not what I saw when I tried to simulate it; but I'll look at it again soon and see if I can figure it out.

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You need a simulation who account for every effects for it to be accurate.

BiduleOhm said:

...That makes sense as you keep the current flowing with D2 (current stored as the magnetic field)...

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Yep.

But honestly that's not really needed, a standard flyback diode would be good enough and simpler

Back around post #16 there are some ways to try and calculate the time the signal takes. There's a couple of methods, but they all were based on measuring the pitiful voltage created by the receiver from the incoming sound pressure waves.

The three approaches in this paper are similar:

• increase the transmit voltage to 120V
• filter the receiver signal
• amplify the receiver signal

Like post #16/17 they're dependent on a strong receiver voltage being induced to trigger the stop time accurately.


Update: This won't work like I was thinking!
Turns out I didn't actually understand impedance. That's okay... deepening my understanding is a part of the journey.
So, where did I go wrong? It was thinking AC is like DC, that once the sound frequency was correct the resistance would be set and could be measured. While true, the "rub" is in the measuring. You can't just apply a bias DC current as a DC current won't be passed despite the sensor "ringing" (that is DC still has open-circuit resistance). If you use AC current, then whatever frequency you use will see the expected resistance of that frequency. Pretty evil, right? To add insult to injury, the MIT Understanding Impedances considers this to be something high schoolers should know. <sigh ;-)>

svetz said:

But suppose you needed just enough sound pressure to get the receiver
to vibrate at the correct frequency and didn't care about the output
voltage it produce?

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Well the problem is anything exciting the transducer will mess your reading (first thing that come to mind is bats).

But you can compensate low levels with good filtering. It's always a balance and a compromise, if your prefer to do filtering than upping the voltage then do that. Of course there's a limit and you can't fix a SNR of 1...

svetz said:

From the datasheet, we can see at the resonant frequency the impedance
of the transducer drops to 500 Ω. A circuit that measures the impedance
might provide a more accurate stop time, not need filtering, not
need amplification, and not need as much incoming sound pressure.

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Yeah but it's not resistance, it's impedance, which means you need to give it some AC signal to mesure it. This graph is mostly used for the transmitter side because impedance changes can mess with your driver (same problems as with loudspeakers and amplifiers in the audio world).

BiduleOhm said:

...Well the problem[s are]...

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Bats don't seem insurmountable, but the AC might be as it could interfere with the resonant frequency.

svetz said:

I found a "reconditioned" replacement anemometer for $18 from the manufacturer based on your idea in post #4 ... but this still seems like a cool project so whenever I get a few minutes waiting on something else I delve into it. Possibly someday I'll actually build one.

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It died... fortunately just the batteries... although the panels are a bit dirty.... so, going to haul the hose up for a quick rinse... ?

Just thought I'd add a reference to a company that builds kits for weather stations based on Raspberry Pi: https://www.switchdoc.com
Not great quality anemometer or wind vane but is nice that you can easily add your own sensors even ones that don't come with the kit.. and easy to get the data to the internet. Also a big bonus that the software for it is all open source.

This one is also interesting; an atmospheric infrasound monitor: https://raspberryshake.org/products/raspberry-boom/

Added to the OP a new hack-a-day based on a car reversing sensor: https://hackaday.io/project/181677-wind-sensor-using-car-reversing-kit

svetz said:

An alternative approach might be a set of wings attached to a strain gauge to measure lift force. Got the idea from:

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We have a weather rock too. When the ice melts I'll share a picture.

svetz said:

Added to the OP a new hack-a-day based on a car reversing sensor: https://hackaday.io/project/181677-wind-sensor-using-car-reversing-kit

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We get high and gusty winds. Something with moving parts, even the chain, would wear out way too fast. Have you seen this product completed?

WYtreasure said:

We get high and gusty winds. Something with moving parts, even the chain, would wear out way too fast. Have you seen this product completed?

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Nope.

But there's a number of store-bought versions you can buy, they're popular on salt-water craft, the National Weather Service is choosing ultrasonic sensors as opposed to mechanical ones.

As the theory and mechanics seem fairly simple, I don't see any reason why a DIY version wouldn't work.

Pretty sure batteries won't leak unless the voltage goes down, but given the salt, humidity, and heat thinking I might want to replace them anyway.

Temperature, humidity, and pressure seem to be spot on. It's harder to say how accurate the wind and rain gauge actually are as sometimes they agree with other local weather stations and sometimes they don't.

It's accuracy goes down as windspeed picks up, so hurricane wind speed reports might be dubious, but for what we normally see day to day it's pretty good.

The haptic sensor range guage seems to do a pretty good job when compared to my other range gauge (how much water collects in the trashcans), but doesn't exactly match the "official" reports. My wife gives me grief because I keep confusing the rate with the amount ; -)


Solar seems pretty good, but I think it's a little too good in cloudy conditions. But at least I can tell when the panels have become pollen coated
based on comparing their output to the input.




So, all in all I'm pretty happy with the no-moving parts and solar powered system.