> For me it sounds like missing spike suppressor diodes.

> As long as several relays are activated the spikes, which are generated by
> switching off another coil will be suppressed by still activated relay co=
ils.
> But when you switch off the last relay there is nothing left which would =
be
> able to suppress the spikes...
>
> Just add a common diode (1N4148 will do) across each relay coils.

Highly likely that he is correct.
Note that peak diode current will be the relay current at switching time.
1N4148 will be find in most cases as peak 1 cycle rating is well above
continuous max - but if problems any 1N400x will usually suffice.

If this does not work a good method is to power the PIC from a
temporary local battery supply. If this fixes things then source is
probably (never certain) via supply. If not it may still be be =A0a
signal path spike but very unlikely. Also induction spike in unusual
cases.

But, relay spike is 99% likely - especially if no coil diodes fitted alread=
y.

Note that adding a reverse diode will slug =3D slow release times
somewhat. this is=A0almost never an issue in this sort of application
but may matter in specialist cases.


=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Russell McMahon

-- =

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