Low cost anemometer, I need some help

Hi All,

I am trying to build a wind speed gauge for home. I have found a bunch of designs online but they mostly use a bicycle speedometer and a look up table. Also the speedometers appear to be limited to about 9 pulses per second which apparently equates to around 100mph with a 28" wheel.

As an alternative, I have a DC motor from a small electric screw driver and I mounted my cup wheel on it. The wind has to be at about

10mph before it starts to turn which is probably OK as it often gusts to 50+.

So the plan is to use a DVM and a variable resistor to adjust the readout from volts to mph if possible. Ignoring any decimal points.

The thing I would really like to have is the highest speed recorded. How would I go about storing the highest voltage achieved since the last reset?

I can build kits etc but I am hopeless at design so a schematic would be good.

Thanks

Dave

Reply to
Dave, I can't do that
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Mmm... I'd think most bicyclists would like to know wind speeds rather less than 10mph -- you can sure feel the effect of the find pushing back on you well below that.

What you want is a "peak hold" circuit. Enter those three words into Google and check out the results; you'll find plenty.

(I'm assuming you're not looking to use a microcontroller here. If you are, then of course you just get one with an ADC built-in and "add software.")

---Joel

Reply to
Joel Koltner

Use a DVM with peak hold ...

Reply to
who where

This is probably a bad idea. There's just too much friction in *both* of these mechanisms. Instead, look for something with much lower friction -- something that "spins easier".

Your "sensor/pickup" can be something optical or "magnetic" so that it doesn't contribute to the losses in the shaft. E.g., you could mount a hall effect sensor someplace proximal to the "wheel" and some number (as few as one) of equally spaced magnets on the "wheel" that pass by the sensor. Or, the equivalent in optical devices.

The sensor can be wired to trigger a one-shot whose output is low-pass filtered and feeds a voltmeter.

Or, use a DPM with "rate" capability like:

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You know you can also *buy* home weatherstations for not much money...

Reply to
D Yuniskis

Agreed, or persist with a cycling computer - it will store the peak speed for you. You just need to play with your bike wheel + cups sensor.

Perhaps an old desk fan blade + bearings with couple of magnets for the bike wheel sensor would be useful.

Reply to
Royston Vasey

Ah! That's an idea! I guess I'm showing my age thinking that a bicycle speedometer has a "cable-in-cable" coupling between the hub and the indicator (with lots of drag). Perhaps an old desk fan blade + bearings with couple of magnets for the bike

Reply to
D Yuniskis

Somewhere I have an article clipped from an instrumentation magazine that described the anemometer on Mt. Washington that recorded the (at the time) highest recorded wind speed sometime in the 30's. As I recall, it was a cup spinner device whose shaft was linked to a set of gears that produced an electric telegraph-like pulse for a set number of revolutions of the spinner. The pulses were recorded on a sheet of ruled paper attached to a drum that turned at a constant rate and against which a pen advanced linearly, recording a deflection in the pen trace for every pulse (the mechanism had been adapted from a tipping rain gauge). The meteorologist determine wind speed by measuring the distance between recorded pulses and consulting a calibration chart.

An electronic analog to that would record a counter reading between pulses, storing them on something like a flash memory stick.

Reply to
Richard Henry

Not an answer to your question, but try looking on line for a Hot Wire Anemometer. It uses a wire which changes resistance with temperature. A current through the wire heats the wire up and the air currents cool the wire. May not be the best choice for a battery operated device, but no friction.

Dan

Reply to
dcaster

I will comment on that after I comment on your next suggestion below.

Yup, but not with a wind speed. They start at around $150. I bought the cup spinner for $11.00 and that's all I have spent so far.

As to the DPM at $264, I **could** buy a weather station for that but I don't have $264 to spare just to find out wind speed. I cannot image a use for it beyond that.

@Royston: You must have missed the 9-pulses per second on the bike speedometer that I mentioned. The cup spinner can be doing 1500rpm, that's 25 pulses per second.

@Dan: Thanks, I did look into the hot wire system but it got too complex for reliable wind speeds. The heating needs to be somewhat proportional to the wind speed. The Amps in at 5mph needs to be a lot lower than that at 50mph.

Dave

Reply to
Dave, I can't do that

Thanks Joel,

I did that and came up with this...

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At the bottom of the schematic and the "Reset" line, what does that mean with the device on the right after the resistor. Is that supposed mean that the base for both transistors is connected after the resistor, or is the first device a 4-wire thing?

Dave

Reply to
Dave, I can't do that

like:

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Try:

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$50.00

Sorry, I don't know what industry(ies) you work in. The DPM is common for industrial process control applications. I have no idea where this unit sits in the range of prices and features -- I only referenced it as I have six of them in the garage (so I didn't have to search for model numbers :> )

Reply to
D Yuniskis

Ha, that's funny. It was that exact thing that got me started on building this one. A neighbor bought one and I quote from the specs, "Wind Sensor: Powered by Thermo-Hygro Sensor," for wind speed that is about as good as a a damp piece of kelp for guessing humidity.

The neighbor was very disappointed and took it back. I told him I could build a real wind speed meter for under 20-bucks.

So far Cup wheel =3D $11 DVM $3.00 Trim pot $0.50 I have to build the Peak-Hold for no more than $6 and I am in under $20

My "industry" is "the Retired," industry.

Thanks Dave

Reply to
Dave, I can't do that

How are you going to calibrate it?

Reply to
Richard Henry

Why were you unable to get indications from very low wind speeds?

I used an old vU meter D'arsonval movement from an old junked out component stereo and I was able to get deflection from VERY tiny amounts of movement/wind.

It was amazed that it was so sensitive that you could see bumps that resembled half waves from the individual armature windings.

You could probably build a circuit that counts those pulses, or you could have the wind mill drive a (larger the better) wheel with black/white marks or flower petals to count optical interruptions.

The opto-interrupter method gets away from the loading effects of measuring voltage or current over a long lossy wire, but generally you'd do part of the signal counting close to the windmill either way, right?

Somebody mentioned an embedded microcontroller with a look up table which is often done where conversion is non-linear.

In this application what feature induces a non-linear response that needs a table lookup?

Why wouldn't it be a straight ratio?

When it comes to measuring wind speed, isn't it LOCATION, LOCATION, LOCATION?

Putting the windmill cups in a spot affected by valley, trees, building walls, eddies from walls etc. would be a huge factor for accuracy wouldn't they?

IE just placing it outside a window would distort the results differently depending on which way the wind is blowing because of the building and or eddies, right?

Just a d'Arsonval movement with a big face driven by a common toy motor and a hand marked scale or face on the meter looks like it would do pretty good if you don't need some rediculous kind of hyper accuracy.

Reply to
Greegor

Hold it out the car window in a windless day. Travel at 20mph in both directions. ;-)

Dave

Reply to
Dave, I can't do that

The wind here goes from no wind to gusts up to 75mph in less than 10 minutes. It is not an uncommon thing to see the forecast stating "gusts to 60mph". The recent 75 was not common, but 50 to 60 happens about 30 days a year. Our Building Code is for 90mph.

Those wind speeds preclude anything bigger than the cup windmill I have which is around 4" or 5" diameter. The next bigger cup windmill was rated at 55mph max and that was only about 2" bigger in diameter.

Dave

Reply to
Dave, I can't do that

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