No, the cap goes between the base and EMITTER,
NOT the collector! Putting the cap between base
and collector is stupid as it couples the back emf
to turn the transistor back on, exactly the reason
you are getting vibration now.

I said clearly in my post to put the cap between
B-E, and if you need extra filtering another cap
across the bottom 2 resistors. The relay itself
has significant hysteresis so a single transistor
driver will work ok IF you put the cap in the right
place! :o)
-Roman



Eke Neehr wrote:

> No, I don4t trying in lab. I4m testing outdoors
> and the relay vibrating when it has to turn off
> in the twilight and turn on the lamp!
> To place a 1 uF cap between collector
> and base don4t works at all !
>
> Regards
> EkeN
>
> > 1. You are trying it in a lab and you have fluorescent lights on
> > 2. The 12V power supply is weak and drops when the relay pulls in
> >
> > In both cases adding a 1uF capacitor between base and collector should
> > help.
> >
> > Peter

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