I was thinking about that too. When the relay stops clicking on and off, is the contact closed or open? Since you are driving this off a sound card, could there be a continuous low or high frequency low level audio signal that is slowly charging your input capacitor, and eventually biasing the transistor on all the time.

Ken

so if its true , whats the solution ??

 

its appearance is Ok, and I didnt get much information if its ok or not with testing it via a multimeter,I will chek this circuit with c945 too

 

Eric,
Thought I was posting to a thread on another forum.

Sorry!

Ken

 

Hello,

Did you actualy measure the voltage?
I would expect a bit lower voltage.
The low base resistor values could also stress the outputs of the MCU.

Bertus

I was thinking the same thing. At least he posted a schematic. It helps to measure Vc, Vb, & Ve with respect to ground in the ON state and the OFF state.

 

yes, because it works with lower resistor on base

That doesn't mean it's not corrected improperly and may, in fact, indicate the connection is incorrect. If the collector and emitter are reversed then the transistor will still work, but with a very low gain (requiring much higher than expected base current to turn on, as you are experiencing). Also the emitter-base breakdown voltage is much lower then the collector-base breakdown voltage, and that may be why the transistor seems to latch on when you try to turn it off.