Hi Nicola,

That is a BLDC motor (Brush Less DC motor). There are couple of app notes on
driving such a motor at Microchip web site if you look at the motor control
notes.

What you should know is that generally speaking you do not need the common,
and for HD motors most of the times there is no sensor therefore you should
look at the sensorless notes I think. If you look for sensored motors you
should be able to get one from CD ROMs.

For the basics MC app notes are definitely good sources, you can even find
one with digital filtering the back EMF (you will see what is that). I think
there is even a controller written in assembly, so should be fun.

Tamas



On Thu, Apr 10, 2008 at 4:55 PM, Nicola Perotto <nicola@nicolaperotto.it>
wrote:

> Hi all,
> i have a harddisk motor and want to control it.
> The motor is brushless but have 4 wire, the fourth is  a common.
> I haven't found anything in the internet about this... any suggestion?
> Thanks
>      Nicola
>
>
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