pic18f2550 noise problem

[jerryd]

edaboard forum,
I'm using a pic18f2550 because it's simple and has the exact number of ports and interrupts needed for my circuit. I use one of the ports to supply a square wave to an LM386n amplifier. I also use a 2 digit 7 segment common cathode display.

This all works but when I'm multiplexing the display it somehow injects some noise onto the output pin of the amplifier. I have all the recommended noise suppressing components on the LM386 and have isolated the wiring so there is no cross talk. Using a scope during this noise there is noise on the power supply or the input pin for the amplifier.

Any suggestions?
jerryd

 

[Easy peasy]

No ckt = no way to diagnose

 

[thannara123]

How the square wave generates ? is it by interrupt method ?

 

[KlausST]

Hi,

Like EasyPeasy said, it's impossible to find the cause if you don't show us all your project.
Schematic, PCB layout, code, scope pictures, your expectation ..

It could be any of the above:
* wrongly dimensionated filters, power supply bypassing (schematic)
* wrong wiring, no really solid GND plane (PCB)
* jittery square wave caused by code oroblems
* wrong measurement method
....

You say you made everything right but ... there's obviously something wrong.
So show us what you did, so we are able to validate it.

Klaus