push button problem (read 2.5 v in off state)

[khalid mostafa]

The below simple circuit does not working probably . why the volt is 2.5 v in off status ?? I think that it should be 0 v

 

[rfredel]

Hello Khalid mostafa,

You are right, the voltage must be "0 V" in real circuit.

But I think, you use only a simulation to control it. In simulation you have not real componets and measure instruments, but ideal components. So your voltage meter has an unlimited input resistance and the capacitor will not discharge by the instrument.

For real test, put a resistance of 10MΩ parallel to the instrument as simulation of the inner resistance. S o the voltage will drop to zero.

Regards

Rainer

 

[khalid mostafa]

Hello Khalid mostafa,

You are right, the voltage must be "0 V" in real circuit.

But I think, you use only a simulation to control it. In simulation you have not real componets and measure instruments, but ideal components. So your voltage meter has an unlimited input resistance and the capacitor will not discharge by the instrument.

For real test, put a resistance of 10MΩ parallel to the instrument as simulation of the inner resistance. S o the voltage will drop to zero.

Regards

Rainer

thank you so much for the fast reply .but where is the volt source ?? the button is off and the cap. is not charged ??
another point ...I'm trying to simulate the human finger act by a push button and a 100pf capacitor . is there a way in isis to simulate it instead ?