How to use a BJT as a switch..

[89Panadol]

How to use a BJT as a switch...I want 2 connected the alarm circuit and UltraSonic Radar...please anyone tell me..

 

[www.electronworks.co.uk]

get two pnp transistors. connect their emitters together and connect these to the power input. Drive the bases low via a 10k resistor. Take the outputs from each collector.

Once again, your posts do not make a lot of sense. If you used proper English, you might get more help.

At a guess, I think the above answers your question.

 

[89Panadol]

oo..then i  connected the alarm circuit to the collector....

 

[audioguru2]

The ultrasonic Radar circuit is not Radar and is not Sonar. It is a simple motion detector with a short range.

It has a transistor output to activate an alarm but I don't know which alarm circuit you have.

 

[89Panadol]

i get the alarm circuit from this website

http://www.redcircuits.com/Page84.htm

how i can connect it to the Ultrasonic radar...

 

[audioguru2]

The two projects are connected together like this:

View attachment 40623

 

[89Panadol]

ooo thank you very much....now i understand how to connect the circuit...and congratulation for fast reply and your help....yahoooo.. ;D ;D

 

[89Panadol]

Is it really work if connected like that..

 

[audioguru2]

Is it really work if connected like that..

Yes.
TR1 will turn on and it will turn on the alarm circuit.

 

[89Panadol]

how about the IC 741 OPAMP...Could i change it like your advice in other forum..

 

[audioguru2]

how about the IC 741 OPAMP...Could i change it like your advice in other forum..

The very old circuit already had its extremely old opamp changed to a 741 opamp. The first opamp needed C3 but the 741 opamp does not need C3.

I would use inexpensive, low noise and wide bandwidth TL071 opamps in this project.