reading, recording anemometer data

I’d like to use an arduino to read and record (say, on a flash drive) data from an NRG#40 anemometer that I salvaged off a fallen-down and abandoned wind monitoring tower.

It has a rotating 4-pole magnet and a stationary coil, and the output is a low level AC sine wave, with the frequency proportional to wind speed. Some questions for which I can’t seem to find answers (that is, answers that I can understand):

  1. can an arduino read the frequency output from the anemometer directly? Or do I need a frequency-to-voltage converter, like a LM2917 chip?

  2. where can I find a sample script I can modify to do the reading and recording of the anemometer output?

TIA!

I see two problems:

Arduino is not happy with AC, and reading a sinewave is a bit complicated.

If you could rectify it and turn it into a squarewave then you could use Arduinos pulsein() function to read it.

Another aproach would be the one you suggest, turn it into a voltage, in the 0 -5V range (no AC, no negative voltages) and read the voltage with Arduinos built in anlog to digital converter.

You can probably use a comparator chip like the TLC3704 or the LM339 (use a pull-up resistor with the LM339) to convert the AC output from the sensor into DC pulses for the Arduino.

Thanks for the replies.

Come to think of it, since I salvaged the anemometer, I’d like to use as many salvaged parts in this project as possible. I have a small collection of all of the computers, modems, and CD players I’ve ever owned. Might there be a TLC3704, LM339, or LM2917 in one of them?

If there are it’s probably a tiny surfacemount component that will make you swear and yell, while trying to desolder it and resolder it without destroyng it.

I can’t think of a place to find a comparator chip in typical electronic junk. I got a bunch of TLC3704 chips from my local FreeCycle group, but of course that was just luck!

LM2917 at digi key are $2.11.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&KeyWords=lm2917&x=15&y=16

I’m doing something similar with my motorcycle. I will be taking pulses from the speed sensor, or the ignition system, using the arduino combined with sirmorris method for storing data on an sd card http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235125412.

The speed sensor and the ignition system(the feed to it) of the bike put out square waves. I will feed the pulses into the arduino where they will be counted and timed, then, by sirmorris method, that data will be stored on an sd card that I can pull out, run the card to my computer and feed that data to the computer via USB into notepad or workpad. From there you can do whatever you want with the data.

Another similar method is to store the data on external EEPROM, but there are some slight encumberances with that system.

I have gotten these methods to work, but haven’t actually placed them on the bike yet. I’ve slacked off in the last couple of weeks; weather is nice and I’ve been doing more riding.

I could post some of the info, later: the arduino coding etc, circuitry, etc. I have get back into the swing of things.

I will keep a check on this site, see what you think.

P.O’T