[sdiy] Mixed-signal problems (dsPIC digital delay project)

yo at vacoloco.net yo at vacoloco.net
Thu Jan 26 18:32:49 CET 2017


I think there are a number of things to try.
Firstly, as someone suggested, try running separate bench supplies. If 
you still get noise, then it's most likely the DAC (as Richie says).

if not, then look at using ferrites to remove AC from the power lines, 
better placed decoupling caps and so on.

P

On 2017-01-26 17:03, Tom Wiltshire wrote:
> Ok, I'll give it a try on the board and see if it helps. Thanks. A
> pair of 100n ceramics from the op-amp power to the virtual ground,
> right?
> 
> But that's trying to limit the effect of the noise on the 9V rail,
> isn't it? Is there any way I can stop it getting there in the first
> place? Is that what the inductors going to the regulators do - stop
> noise coming back from the far side of the regulator?
> I think I need to understand better where this noise is coming from and 
> why.
> 
> On 26 Jan 2017, at 16:32, yo at vacoloco.net wrote:
> 
>> I totally missed that, too busy looking at PSU problems and grounds.
>> yes, decoupling caps (but they'll need to be to your virtual ground).
>> 
>> On 2017-01-26 16:11, Jason Tribbeck wrote:
>>> You don't seem to have any decoupling capacitors for the op-amps.
>>> And I would also suggest small inductors (or even ferrite beads) 
>>> going
>>> from the 9v line to the input of each of the regulators.


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