Re: [SI-LIST] : Request for help

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From: Cengiz Aydin (caydin@ee.bilkent.edu.tr)
Date: Thu Oct 26 2000 - 00:05:38 PDT


Hi Yasser,

It seems to me as you have a problem with
your power and ground distribution. So,I
advise you to check the VCC and GND lines.
You did not give any information about your
board's structure, I mean, whether it is a
multi-layer or two-layer board, every
IC has bypass capacitors, etc. Assuming
it is a two-layer prototype board, no power planes,
and you placed decoupling capacitors to each IC,
probably, you have very thin VCC and GND lines,
and they route relatively long paths, so, they perform
a good antenna (inductance) to pick up everthing around.

Before making a new PCB with thick VCC and GND
distribution lines, you may try to use a GND plane
as a shield. Take a copper plate ~0.5 mm thick.
Cut it at the same size as your PCB. Place a layer
of insulator paper between your board and this copper
plane. This kind of insulator paper is used in the transformers
for the purpose of insulation between windings.
At the end, you will have a stack which consists of
your board, the insulating paper and the copper plane.
Connect one GND point of your board to this
copper plane with a wire. And, finally, connect another wire to
the copper plane and connect the other tip to the EARTH.
Generate the same disturbing signals and check for the
hang up.

You may see this kind of solution in some
electronic products with two-layer PCBs , e.g.,
some old Z80 home computers.
I hope this works for you too.

Regards,

Cengiz AYDIN

Researcher
Bilkent University
Faculty of Engineering
Dept of Electrical and Electronics Eng.
Bilkent 06533
Ankara
TURKIYE / TURKEY

On Wed, 25 Oct 2000, yaserh wrote:

> Dear Sir :
>
> I have a problem in a microcontroller board works with a linear power supply from a power transformer.
> The problem is when any device is in the AC plug with my board switches on or off my board hangs.
> I have checked my +5V supply with the Digital storage oscilliscope and i find in switching the other devices i found spike of level +6V for duration of 100 ns over the +5V and in other times it's -6V for duration of 100 ns down the +5V. I have reviewed my PCB i found no problem. I put a line filter with my AC line it does not solve the problem.
>
> I need to know from where this spikes come to my circuit and how i can solve this problem.
>
> Waiting for reply
> With my best regards
> Yasser El-haddad
>

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