interfacing a stepper motor acting as a generator

Hi

I am an Arduino novice. I needed some help regarding interfacing a stepper motor generating AC . The Arduino board should be able to detect some parameter for eg:- variable voltage generated at different shaft rotaion speeds.

In short how can i get meaningful parameters from a stepper motor acting as a generator.

Any help is appreciated.

best nitin

Interesting. Why a stepper motor?

But anyway, you can get a DC signal that will indicate speed of rotation (as long as its fairly fast) just by rectifying and smoothing the output from one of the coils (http://en.wikipedia.org/wiki/Rectifier).

A single diode will be fine, but put a capacitor in parallel with the load resistor in the wikipedia diagram.

Select values of R times C to be significantly larger than the maximum anticipated period of rotation. R and C in Ohms and Farads.

Check it out and experiment with a scope or multimeter, to make sure that the maximum output is less than 5V for the fastest possible rpm and is smooth.

If its too high, then you may want to use a potential divider to drop it within range. Remember this adds to the load resistance.

If the signal is too small, then you will need to learn about opamps.

To be thorough, you should protect the analog input with a Zener diode. Search for posts on protecting inputs with a zener diode.

There are, of course, many ways to skin this cat.

(1) us a comparator to watch for zero crossing and generate a clean pulse to feed into the Arduino, then: (a) use it to trigger interrupts and time these to measure pulses in the range of 20 per second down to hours per pulse (b) feed it into the hardware timer and read the timer in software. This will cover pulse rates from maybe 10/sec up to many KHz

(2) rectify and filter the signal and use a voltage divider to feed an analogue input. Then you can use multiple voltage dividers feeding multiple analogue inputs to measure different rotational velocity ranges.

You should be able to measure the rotational velocity reasonably well from a few degrees per minute, up to the point where it flies apart -- certainly up to several thousand RPM.

Hi

thankyou very much. I will sort out the motr issue and then get back for any more help. Thanks again.

One of the slickest designs I've seen for a propeller clock used a stepper. They fixed the shaft and spun the body. Not only did they use the output from one or more windings to power the electronics, they also used the output from one for timing. By controlling the RPM of the body precisely, they got pretty good accuracy out of it.

A google search for something like "propeller clock stepper motor" should turn it up.