how to minimize electrical noise effect on microcontroller environment

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rdubhashi

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hi everyone,
i developing a cyclic timer using pic controller..
which will on for 24 hr.
now when the timer is ON and if i jus simply on/off any electronic appliances which r connected to the same board.
then my whole system gets RESET.
so my question is how to overcome this problem.

thanks for ur time...
 

It is odd, this comes up here semi regularly, but I have used many, many pics in commercial products and don't think I have ever seen this behaviour.

Checklist:
  • Decoupling (100n right at the power pin) plus some bulk cap somewhere on the board.
  • Groundplane.
  • IO not connected directly to the outside world (Always causes trouble), at least use some series resitance and clamp diodes, opto isolation is better).
  • Relay drivers have catch diodes and sane track routing.
  • Switching power nets do not run runder the pic.
  • Power supply does not glitch when switching load (For example if the load has a huge input capacitor and shares the power with the pic....).

A lovely gotcha for newbies with some of the smaller pics is that they sometimes have 2 ground pins, this is not an invitation to use the pic as part of a ground net on a single sided board (Yes, I have really see that done)!

Regards, Dan.
 

On some PICS you can set the MCLR pin to an IO pin. This solved a reset problem for me many years ago.
 


thanks for ur replies...
But still same problem is there..
I m using pic 16f877a...
 

If you are using a breadboard to test your design, all leads will act as antennas and receive the noise from the power lines.
If your power supply is too simple, it may also let the glitches through on the supply voltage, and cause the PIC to reset.

Show us a schematic and a picture of your design. This will make it easier for us to advise you
 

Hi,

it might not help you, but i completely agree with Dan.

The problem is called EMC (electromagnetic compatibility).
Also look for ESD.

Both problems are well known and there are a lot of documents on "how to" avoid these problems.
Look for tutorials and documents and read it carefully.

Klaus
 

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