Yes, i was thinking about that. the 12 VDC is from a switching laptop power=
 supply. Using my sound card as an "oscilloscope" i see that there is a LOT=
 of hum in the ground signal, but i don't know how to remove it.. However i=
'll repeat that: the PIC seems to be working perfectly, except for the pwm =
module. (As far as now the program uses only DIGITAL and ANALOG I/O and the=
 PWM module)

> Date: Tue, 27 Sep 2011 10:51:33 -0400
> From: mark@pixeltrickery.com
> To: piclist@mit.edu
> Subject: Re: [PIC]PIC18F2550A, Pwm doesn't work when using on external po=
wer	supply
>=20
> On 9/26/2011 12:57 PM, Jacopo Monegato wrote:
> >
> >
> > Any suggestion? I already changed a couple of capacitors in the supply =
ciruit, but nothing changed. the circuit is:
> >
> >
>=20
> what is the source of the 12VDC being supplied to the circuit ? Is it by=
=20
> chance from a switch mode supply  ?  Anytime I hear someone say that=20
> changing the power source changes the circuits performance I start with=20
> that. Try powering the circuit from a battery vs a power adapter. =20
> Sometimes power supplies of switching designs maintain some connection=20
> to the wall outlet voltages which would mean you and the local=20
> environment are maintaining some connection to the circuit under test.=20
> You touch a pin altering the flow of current.  I went through this with=20
> a circuit that would perform odd and found that when I put my foot on=20
> the floor is when it was behaving odd. Turns out the power supply was=20
> very dirty and me placing a foot on the floor was completing the loop.
>=20
>=20
> --=20
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
 		 	   		 =20
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.