[SOLVED] Measuring speed of generator/motor

I am trying to measure wind speed by attaching a fan to a generator. I want to find the easiest way to output the voltage and speed to my laptop. I know I could use back EMF but I don't know how to use it.

A generator will output a voltage when it's rotated. That's no "back EMF" involved. That term is usually used with motors.

How will you calibrate your device?

Hello!

You can use a sensor attached to the blades or a encoder on the fan to measure the speed.

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To obtain the response of output voltage to shaft RPM, you can use a paint mark on the shaft and use a simple pulse counter with an optical pickup to measure RPM.
Make sure the generator output is not loaded, otherwise the output voltage will drop due to the load.

Thank you for all the suggestions I will try them and get back to you. The other problem i am having is i don't know a way to output the data to my laptop.

yosef321 said:

Thank you for all the suggestions I will try them and get back to you. The other problem i am having is i don't know a way to output the data to my laptop.

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There are two possibilities:

1. your wind generator has a DC output. Then you must use and ADC,analog-to-digital converter, that converts the DC voltage into digital code you can then use. The easiest way is to get a digital multimeter (DVM) with an USB interface you directly plug into your PC. A program CD comes with the DVM and you can use it directly.

2. Your wind generator produces an AC voltage. Then you can use the DVM as above, only switched to AC volts range. Or you have to use a "sound card" or an audio processor plugged into your PC or a laptop. Then make sure your voltage output is adjusted to sound card maximum input, e.g. by a potentiometer.

3. If your wind device can generate pulses proportional to RPM, then you can use a DVM as above if it has a frequency counter range. Or you can use a laboratory counter with a PC interface.

Thanks again to all the suggestions.
I solved this problem by directly connecting the generator to an Arduino board and got the voltage using this instructions found here **broken link removed** (ignore the connection to the 5V). Then using a formula I converted the voltage to speed.
This might be a bit more complicated then some of the other solutions but it worked best for me.