Re: gEDA-user: buzzing board

[Dave McGuire <mcguire@xxxxxxxxxxxxx>]

On Sep 13, 2007, at 12:55 AM, DJ Delorie wrote:
>>    Is it convenient to try putting an choke in series with the OLED's
>> power supply line, with the OLED's bypass capacitor on the OLED side
>> of the choke?
>
> Hmmm...  100uH power inductor, no change.

   Crap. :-(

>>    I've only used those two methods, aside from probing around with
>> an oscilloscope to look for the noise.  One other trick that I've
>> not tried (if anyone can comment on this I'd appreciate it) is to
>> use an inductive pickup probe to look at the *current* waveforms on
>> the supply lines to different parts of the circuit, and see what
>> corresponds to the noise you're hearing.
>
> I don't think my parallel-port scope is sensitive enough for that.
> Plus, anything with a coil just picks up magnetics from the switcher's
> inductor, but the switcher isn't the supply that provides the +12v.

   True. :-(  You might be able to temporarily shield that inductor,  
but that's a shot in the dark.

>>> 2. What kind of components *can* make that kind of noise?
>>
>>    Inductors and PCB traces, mainly...but I suppose nearly anything
>> probably could, to one degree or another.
>
> PCB traces?

   Yes, they can actually resonate.  I know you've been working with  
desktop computers for a very long time (I used DJGPP in ~1992)...have  
you ever noticed a "squealing" sound coming from a machine when it's  
busy, changing with processor activity?  Sometimes that's the power  
supply, but it's usually traces on the motherboard.

            -Dave

-- 
Dave McGuire
Port Charlotte, FL
Farewell Ophelia, 9/22/1991 - 7/25/2007





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