At 09:48 p.m. 14/11/01 +0000, you wrote:
>Hi all,
>Having a problem or two with a pic circuit that either resets or hangs in=
=20
>mid program.
>It has a lot to do with 2 relays switching 230v motorised valves(domestic=
=20
>heating 'zone' type)

If you are concerned with those relay=B4s put the snubber across the coil,=
=20
but let you tell from
my experience.
If you have an oscilloscope monitor your supply voltage, you may have a=20
week supply,
just to be sure the switcher doesn=B4t screws you up.  But .....
the problem most likely no is where you are looking for, look for the 84=B4s=
=20
oscillator.

If your PIC is very sensitive to noise, check your oscillator setup.
If you are using a 4 or 20MHz crystal, set the OSC bit to HS !!,
look into the caps !!, they may be to small, try 22p or bigger.
put in new one=B4s anyway and try again.
Don=B4t forget to put a 100n cap on the /MCRL pulled high by a 10k resistor.
Check the crystal type, if it=B4s the correct type.
Use 1uF Tantal caps on the power pins, the are lot more effective than other
caps as electrolytic or ceramic types.
If everything is correct, the drawing below is perfect and should not give
any problem. Don=B4t forget the diode in parallel to the relay coil, but=
 even
without should not  be a problem.
Let=B4s see what you got.

Friedel




>I have snubber devices across the relay contacts but wondered whether=20
>anybody had experience in making the pic circuit 'bulletproof'(if that is=
=20
>possible)

I have gone down that road, and it cost me a lot of everthing, money, time,=
=20
reputation and so on.

>In short i.m using a f84a,the psu is encapsulated switchmode dc=20
>supply(230vac in 24vdc out) extra smoothing and a 7805 basic circuit.I=20
>have a brown out external circuit and 0.1uF across the supply pins to the=
 pic
>Anybody any tips as i,m pulling what little hair i have left out
>Dave
>
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