Anemometer with bike speedomometer

[BBQSteve]

Has anyone here thought about using a cheap bicycle speedometer to record wind speed. I just built one and it seems to work great, especially the sensor (reed switch and magnet). Only problem now is getting the data from the speedometer digitally into the computer. Anyone have any ideas?

The speedometer I used is made by Bell and probably available everywhere bikes are sold.

BBQSteve

[beteljuice]

There are several threads on the web about constructing these, and I vaguely remember someone who did a "How To" for a digital Seiko unit which included where to cut and join on the PCB etc. but I can't find it now

See if anything here helps: http://www.physicsforums.com/showthread.php?t=357599

[mcrossley]

No really helpful but I made a propeller driven 'speedo' for a sailing boat from a bike computer once.

[BBQSteve]

Good link, thanks.

BBQSteve

[AllyCat]

Hi Steve,

Presumably you've added 3 half-pingpong balls (or similar) to arms and measure the revs with the cycle computer? That's probably the best/easiest solution for a measurement indpendent of direction. The only real issue is calibration, I believe the circumferential speed is about 30% of true windspeed (but depends on the exact mechanical detail).

The referenced thead also has some bad ideas, for example I think that most computer fans use an "electronic commutator" so they won't work at all as a voltage generator.

But as you say, the diffcult part is getting the data into a computer (and logging it). I have wondered about "reading" the LCD with a webcam (or even dedicated phototransistors) but why bother when it (and much more) can all be done by Fine Offset kit for less than £100/$100 ?

Cheers, Alan.

[mcrossley]

I have wondered about "reading" the LCD with a webcam (or even dedicated phototransistors) but why bother when it (and much more) can all be done by Fine Offset kit for less than £100/$100 ?

I have a friend who has an automatic meter reading/logging system for his gas meter based on a webcam and character recognition software

[Gina]

I have wondered about "reading" the LCD with a webcam (or even dedicated phototransistors) but why bother when it (and much more) can all be done by Fine Offset kit for less than £100/$100 ?

I have a friend who has an automatic meter reading/logging system for his gas meter based on a webcam and character recognition software

I can understand doing that where you can't gain access to the meter itself (at least, no legally) but it seems a strange way to do it for a weather sensor. A magnet and read switch work well enough and there are several ways of connecting a reed switch to the computer.

[BBQSteve]

Alan,

I have a fine offset up and working. The bike speedometer is an experiment as well as a project. I was reading some of these BIY threads, thought I have all I need, let's build one. I like to build things and use my mind now that I am retired.

Yes I used ping pong balls, arrow shaft for axis, medicine bottle cap and a precision ball bearing. Seems to work real well except that you can not program the speedometer exactly. Where the diameter comes out t0 638.37mm, you have to use 638. So this throws the speed and distance off a little. I also have a HandyBoard from MIT, but it is a serial interface and I only have computers with USB, so I am now looking for the interface for USB. As soon as I find it, I will write a C program to read the data and continue with my BIY weather station.

Calibration you figure is 30% off you say. Why is that? I understand the resistance of the ball bearing, although with this bearing only minor, but what else should be taken into account?

BBQSteve

[AllyCat]

Hi Steve,

No, what I meant is that if the wind is (say) 30mph, then the cups move at about 10mph. The reason is that whilst one cup (and arm, etc.) is moving with the wind, two (with rounded faces) are moving against the wind. Somewhere I saw a description of the calibration factor, but for now just see Wikipedia.

AFAIK, almost all anemometers need independent calibration except perhaps to a lesser extent the "soniic" (time of flight) type. For this reason I did develop an ultrasonic anemometer many years ago, but it wasn't a trivial project.

Cheers, Alan.

[mcrossley]

Calibration is what a car sun roof and a broom handle are for aren't they?

[Tau Bootis]

Don't forget the GPS!

[AllyCat]

Hi,

Maybe with a long broomhandle on a still day (and sadly my car has aircon not a sunroof). Also, I will add that my "project" was actually concerned with measuring the transient speed/volume of air from a human lung, not simply windspeed.

Cheers, Alan.

[apenwith]

Hi
I also built one just for fun - I had a spare fine offset anemometer head - and a bike computer so it seemed like a good idea to make a hand held unit. It calibrated quite well against a sailing anemometer.
There are a couple of serial to USB converters and the firmware in one sort is better (there's a thread somewhere that recommends the best) - not too expensive.
Regards
Alan