Need help in a small transistor project please

[shubham123]

I have to make a project on 'Transistor As A Switch' and draw a graph between the input & output voltage showing the cut-off region,saturation & the active region.
I have attached the circuit diagram[b].The problem is that I dont know what values to take for the various components[/b].

I tried making it with BC547 or BC 548 transistor,100k and 1k as Rb & Rc respectively,3volt for Vbb and Vcc(varied the voltage using a 10k potentiometer),Multimeter as Vi and Vo to measure the input and output voltage.[b]Could not get any significant result,the votage kept varying a lot[/b].

From what I understand,when Vbb will be less than 0.7V then multimeter Vo reading is equal to Vcc.As Vbb increases above 1V,Vo decreases.But as I said there was irregular voltage in the multimeter Vi.

[pebe]

Your circuit is too big to view comfortably and you are using some unusual symbols. But I think your problem is that you are measuring the base current voltage source, instead of measuring the voltage actually at the base.

[shubham123]

I made the circuit again using the following components:
BC547 transistor
Vbb = 1.5volt cell (100k potentiometer for varying Vbb)
Vcc = 3volt cell
Rb = 680k+680k+120k resistors in parallel
Rc = 10k resistor

I got some reading at Vo & Vi.As I increased Vi,Vo decreased by a small amount(approx. 0.1volt decrease in Vo with every 0.2volt increase in Vi).I think this lies in the active region.
Now I want to know how do I increase the range of Vi so as to get 0.5volt as min. voltage(currently getting 0.9volt to 1.6volt using the above components)

I was given to understand that Vo would near zero volt as Vi becomes greater than 1volt
and Vo will be equal to Vcc when Vi is equal to or less than 0.6volt.
I have attached my reading of Vi & Vo.
Thanks a lot
[img]http://www.electronicspoint.com/attachments/6178d1352690199-need-help-small-project-please-capture.jpg[/img]

[pebe]

I say again...........!
You are measuring the base voltage source - not the voltage directly at the base.

The transistor will start to conduct when Vb=0.6V, and will be well into saturation with Vb=0.8V

[shubham123]

Just got what I think is the correct readings.I had connected the potentiometer & transistor wrongly.I have attached the new readings.Let me know if they are correct.
Thanks a lot for answering.

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[pebe]

I am amazed you can put 3.1V on to the base of a BC547 without popping it. Is that voltage actually measured between the base and emitter pins of the transistor?