Thanks for reminding me on the 25mA limit. I was too
involved in understanding the theory at that moment of
time :) I will decouple it from the pin itself.

John.


--- Michael Rigby-Jones
<Michael.Rigby-Jones@bookham.com> wrote:

> 
> 
> >-----Original Message-----
> >From: piclist-bounces@mit.edu
> [mailto:piclist-bounces@mit.edu] 
> >On Behalf Of John Chung
> >Sent: 02 April 2007 05:31
> >To: Microcontroller discussion list - Public.
> >Subject: [EE] Buzzer puzzle.
> >
> >
>  I checked the current
> >consumption during Q and it was draining about
> 32mA.
> >
> >Why do I need a resistor in
> >series?
> 
> The PICs I/O pins have an absolute maximum rating of
> 25mA!
> 
> Also if this is a magnetic device then you will
> probably be getting some nasty current spikes when
> you switch it off which could cause problems with
> the PIC.  The resistor is limiting both the DC
> current and any transient currents when you set the
> port pin low.
> 
> If you want to use this device purely as a buzzer
> then I suggest that you put a resistor in to limit
> peak current and also AC couple it (i.e. put a
> capacitor in series) to prevent excessive current
> being drawn if the PIC's ouput remains high. 
> Connecting a diode accross the buzzer (cathode to
> PIC pin, anode to ground) will help suppress any
> spikes.
> 
> Regards
> 
> Mike
> 
>
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