f to the V

A one-shot followed by a low-pass filter will convert f to V. But if you are feeding that to a uC again, it might be easier to just let the uC measure the frequency directly. In that case you don't need an ADC, less external components and it's probably more precise.

A standard AC motor doesn't produce AC when you turn it. You can get small low cost encoders or take an old mouse to pieces.

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BTW, when I read the title of this email I thought it was perhaps a rap song: "From the f to the V to the fly M.C. ..."

Wind vane or anemometer? A wind vane measures direction & may often produce a frequency approaching 0, even in a gale. An anemometer measures speed, & may also produce a frequency approaching 0 (just not in a gale).

JM

ok. thank you everyone who comment on. Yes this is a anemometer setup which is connected to PC parellel port via ADC.

As one of you said " A standard AC motor doesn't produce AC when you turn it" according to the theory, this acts as a generator. ain't it ? so it must produce some voltage.

Anyway if I replace this idea by "mouse setup" How can i measure the speed it turns ?

thanks > scilent-project wrote:

If by "standard AC motor" you are referring to a squirrel gage motor, it does not necessary start to produce electricity, when you turn it. It usually requires three capacitors between the phases to produce a reactive load, before it generates some initial voltage. Alternatively, installing a small permanent magnet (from the refrigerator door :-) on the rotor will help the startup condition. On a squirrel gage motor/generator, you should compensate for the slip, if you need accurate measurements.

I would suggest using a bicycle dynamo to generate a signal frequency proportional to the speed of rotation. The dynamo has some environment protection, starts up without a problem and is a synchronous with the rotation speed.

Paul

If you have the motor, why not try it ?

The mouse needs to be old enough, to have the rotary encoders :)

Those use slotted wheels, and opto-interruptors, to give two quadrature signals (so you can get speed and direction)

You would need to test that at maximum windspeeds, to check the opto+load was able to keep up, as these give many pulses per rev.

Another method is a magnet(s) + reed switch(es) : that's quite rugged, and suited to outdoor usage. Measure the period in a uC, and derive the wind speed from that, probably with a lookup table to correct for non-linearities.

-jg

They do act as generators but only when they are running under power. You need somekind of magnet to self generate. If you want to use an ADC then you need a DC motor. You can measure speed using frequency, like your post title would suggest, with a mouse encoder or you could use the main motor from a hard drive which will also give you pulses as it turns.