noise measured in cro screen.

[hiren.dave@bhuved.com]

hi,

when i connect a circuit with CRO. every time i get noise on cro weather it's circuit or output pin of microcontroller. noise is very small approx. 100mV. i want to remove this noise. how to remove this noise.

 

[Sceadwian]

If you touch the probe leads together does the noise still exist?

 

[aljamri]

Good earthling will minimize the noise. you mentioned the amplitude, what about the frequncy of the noise? if it is the same every time this proves my suggestion.

I'm using a large piece of metal sheet and put above any insulating medium such as paper or plastic and connected it to the ground and put my circuit on the top, this eliminates much of the noise.

 

[Sceadwian]

The first step is to check the CRO itself. If you short the ground/signal leads of a CRO and the noise is still there then regardless of it's amplitude or frequency you know it's coming from the CRO not externally. If it's comign from the CRO outside of getting a new scope or repairing the existing one there is no fix, so asking more advanced questions about the existing circuit is irrelevant until the original question of 'has the CRO been tested' is answered.

 

[circuitspecialists]

You should try using a very short ground lead on your scope probe. Oftentimes the ground lead will pickup noise. Most scope probes come with a "spring" clip that can be used as the ground lead. If the noise is diminished using this very short ground lead, you are seeing noise pickup. If the noise level is the same then the noise in being produced by your circuit.

 

[ericgibbs]

hi,

when i connect a circuit with CRO. every time i get noise on cro weather it's circuit or output pin of microcontroller. noise is very small approx. 100mV. i want to remove this noise. how to remove this noise.

hi hiren,
On almost every digital circuit you will see some 'noise' on your pins when using your scope.
The recommended decoupling of the power lines will help to reduce the noise to a level that does not cause mis-operation of your circuit.
What capacitive decoupling do you have on your PIC supply pins.?

I doubt that its possible or necessary to remove all the noise produced by the switching in digital circuit.

E.

 

[Sceadwian]

The original poster seems to have abandoned this thread, never posted results of a basic debug (shorting the CRO's inputs together with a shunt and measuring the noise then) than will rule the scope itself out, then measure the noise again with just the leads shorted to each other. Also as everyone seems to be asking answering basic questions about the type of noise they're seeing is critical in answering the question.

If he's using an older scope 100mv of noise isn't unusual at all. I had more than that on my last one.