How to speed control of  50W 12V DC motor with PWM

Dear Gurus,

I am a newbie in arduino, and now excited to make a controlled of PH DC for my aquarium, this PH motor is a 12V 50W DC motor, and I plan to control the debit of water by controlling the speed of this motor using PWM technique. Any master and gurus could explain and show me the drawing and what are the components should I use ?

Thanks in advance Regards :)

see:- http://www.thebox.myzen.co.uk/Tutorial/PWM.html

and :- http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

for a start

Thanks Mike, really appreciate with your help, can I use only single TIP 102 to drive the motor ? Can it withstand for 50W/12V=4.2 Amps in the collector ?

It can handle 8 amps. Next time search PDF in the internet as I have just done for you! ;)