(SOLVED)Basic circuitry

[Ricemarine]

***SOLVED/FIXED***

Diagram of what the circuit should be
What I did.

Now what I should be doing is getting a voltage of 5V for V(ce). The problem is. with the red wire connected next to the pot I get a voltage of 9.08v. With it gone I get a voltage of 0.06V...

What is the proper way of hooking this up correctly?

Thanks.


Thanks PottedMeat, Born2bwire, So, TuxDave, and SaturnX

 

[PottedMeat]

Are you sure you have the 10 turn potentiometer connected correctly? And the transistor for that matter? From the angle it looks like there are only 2 connections to the pot and 2 to the transistor. When reading the transistor datasheet make sure you look for "BOTTOM VIEW" or "TOP VIEW". That's screwed me over before. Whats the green wire for?

 

[PottedMeat]

It helps to draw a picture too - draw a little picture of the transistor (off the datasheet) with the leads labeled and lines connecting it to the pot. Then copy it to the breadboard. Don't bother trying to remember the pinouts in your head.

 

[Ricemarine]

Originally posted by: PottedMeat
Are you sure you have the 10 turn potentiometer connected correctly? And the transistor for that matter? From the angle it looks like there are only 2 connections to the pot and 2 to the transistor. When reading the transistor datasheet make sure you look for "BOTTOM VIEW" or "TOP VIEW". That's screwed me over before. Whats the green wire for?

The green wire I accidentally left there. It didn't alter the results though. The transistor is connected correctly from what I can tell. Collector top, Base middle, Emitter bottom, where the round side is on the left (top view).

How are you supposed to connect the pot correctly in parallel? I connected the 10k resistor to the top prong and the 20k to the middle prong and nothing to the bottom prong.

It's a 2N3904 transistor btw.

 

[Born2bwire]

Originally posted by: Ricemarine

Originally posted by: PottedMeat
Are you sure you have the 10 turn potentiometer connected correctly? And the transistor for that matter? From the angle it looks like there are only 2 connections to the pot and 2 to the transistor. When reading the transistor datasheet make sure you look for "BOTTOM VIEW" or "TOP VIEW". That's screwed me over before. Whats the green wire for?

The green wire I accidentally left there. It didn't alter the results though. The transistor is connected correctly from what I can tell. Collector top, Base middle, Emitter bottom, where the round side is on the left (top view).

How are you supposed to connect the pot correctly in parallel? I connected the 10k resistor to the top prong and the 20k to the middle prong and nothing to the bottom prong.

It's a 2N3904 transistor btw.

Well it seems pretty obvious from the provided circuit diagram that you should have connections on all three terminals of the pot.

*BARF* You and your edits.

 

[So]

Looks like you've got everything that's supposed to go to the base shorted to the collector. (assuming that your BJT is E - C - B when looked at as you have it set up)

 

[Ricemarine]

Originally posted by: So
Looks like you've got everything that's supposed to go to the base shorted to the collector. (assuming that your BJT is E - C - B when looked at as you have it set up)

C-B-E from top view. So I fixed the short so that the bottom terminal of the pot is shorted, but I'm still getting 0.07V. I double checked my pot, and it is the 100kohm pot. The 10k is parallel to the pot which goes to C. The 20k is bridging the base to the middle terminal of the pot. Then the emitter is shorted parallel to the pot and the voltage source.

Originally posted by: Born2bwire
Well it seems pretty obvious from the provided circuit diagram that you should have connections on all three terminals of the pot.

*BARF* You and your edits.

This is why I love the internet .

Edit:
Voltage across 20k, 2.21V
Voltage across 10k, 8.46V

 

[TuxDave]

I need better pictures to see the connections of the resistors and the bjt. It's hard to see what's connected to what. And where are the terminals of the pot?

Are you 100% sure it's CBE left to right? Because then you have the BJT backwards.

 

[So]

Originally posted by: Ricemarine

Originally posted by: So
Looks like you've got everything that's supposed to go to the base shorted to the collector. (assuming that your BJT is E - C - B when looked at as you have it set up)

C-B-E from top view. So I fixed the short so that the bottom terminal of the pot is shorted, but I'm still getting 0.07V. I double checked my pot, and it is the 100kohm pot. The 10k is parallel to the pot which goes to C. The 20k is bridging the base to the middle terminal of the pot. Then the emitter is shorted parallel to the pot and the voltage source.

Originally posted by: Born2bwire
Well it seems pretty obvious from the provided circuit diagram that you should have connections on all three terminals of the pot.

*BARF* You and your edits.

This is why I love the internet .

Edit:
Voltage across 20k, 2.21V
Voltage across 10k, 8.46V

You need a better picutre, because it looks like you built this: Img_2871.jpg

 

[TuxDave]

http://pics.bbzzdd.com/users/xevadex/fixed.jpg

Lemme know what you think. I can't see the terminals of the pot so I drew on top of it my best guesses of where the terminals are and what they should represent.

 

[Born2bwire]

Originally posted by: Ricemarine

Originally posted by: So
Looks like you've got everything that's supposed to go to the base shorted to the collector. (assuming that your BJT is E - C - B when looked at as you have it set up)

C-B-E from top view. So I fixed the short so that the bottom terminal of the pot is shorted, but I'm still getting 0.07V. I double checked my pot, and it is the 100kohm pot. The 10k is parallel to the pot which goes to C. The 20k is bridging the base to the middle terminal of the pot. Then the emitter is shorted parallel to the pot and the voltage source.

Originally posted by: Born2bwire
Well it seems pretty obvious from the provided circuit diagram that you should have connections on all three terminals of the pot.

*BARF* You and your edits.

This is why I love the internet .

Edit:
Voltage across 20k, 2.21V
Voltage across 10k, 8.46V

I know, I'm like the Anti-Mary Worth. The emitter, bottom terminal of the pot, and the negative terminal of your power supply should be shorted together. You are not supposed to leave any floating nodes. I think it was mentioned before, but your 20 KOhm connection is wrong. It does not look like you have the resistor hooked up at all to the base. Instead, you have a wire from the pot going to what may be the connection to the base. I don't know what you are doing with that 10 KOhm resistor though. It looks like you have it connected to the same node as the 20 KOhm resistor which is wrong. It's really difficult to try and debug a breadboard that from a picture that only shows a part of the setup.

 

[SaturnX]

I can't really see what's going on there, but here's how it should be connected..

bjt_cct.jpg

It doesn't look like you've got the pot connected right, you need to connect the main terminals across a potential difference, and as you adjust it, it will vary the resistance between the positive terminal and the "middle" terminal.

 

[Ricemarine]

Originally posted by: So
http://pics.bbzzdd.com/users/TheJBW/Img_2871.jpg[/L]

Updated
Edit
Where I connected the + terminal for the 9v battery from the top to the middle terminal of the pot changed the voltage to 0.03V.

Originally posted by: TuxDave
http://pics.bbzzdd.com/users/xevadex/fixed.jpg

Lemme know what you think. I can't see the terminals of the pot so I drew on top of it my best guesses of where the terminals are and what they should represent.

Does that really fit? Oh... and uhh... although it shouldn't be much of a mistake , C,B,E vertically downward... I think I confused you since you inverted C,B,E.

 

[TuxDave]

Originally posted by: Ricemarine

Originally posted by: So
http://pics.bbzzdd.com/users/TheJBW/Img_2871.jpg[/L]

Updated
Edit
Where I connected the + terminal for the 9v battery from the top to the middle terminal of the pot changed the voltage to 0.03V.

Originally posted by: TuxDave
http://pics.bbzzdd.com/users/xevadex/fixed.jpg

Lemme know what you think. I can't see the terminals of the pot so I drew on top of it my best guesses of where the terminals are and what they should represent.

Does that really fit? Oh... and uhh... although it shouldn't be much of a mistake , C,B,E vertically downward... I think I confused you since you inverted C,B,E.

Wait what. CBE is vertical? That's impossible otherwise they'll be shorted.

 

[Ricemarine]

Originally posted by: TuxDave

Originally posted by: Ricemarine

Originally posted by: So
http://pics.bbzzdd.com/users/TheJBW/Img_2871.jpg[/L]

Updated
Edit
Where I connected the + terminal for the 9v battery from the top to the middle terminal of the pot changed the voltage to 0.03V.

Originally posted by: TuxDave
http://pics.bbzzdd.com/users/xevadex/fixed.jpg

Lemme know what you think. I can't see the terminals of the pot so I drew on top of it my best guesses of where the terminals are and what they should represent.

Does that really fit? Oh... and uhh... although it shouldn't be much of a mistake , C,B,E vertically downward... I think I confused you since you inverted C,B,E.

Wait what. CBE is vertical? That's impossible otherwise they'll be shorted.

Or I meant, from your picture... you wrote CBE, it should be EBC. (Although it could be you found out what's wrong?)

 

[TuxDave]

Originally posted by: Ricemarine

Originally posted by: TuxDave

Originally posted by: Ricemarine

Originally posted by: So
http://pics.bbzzdd.com/users/TheJBW/Img_2871.jpg[/L]

Updated
Edit
Where I connected the + terminal for the 9v battery from the top to the middle terminal of the pot changed the voltage to 0.03V.

Originally posted by: TuxDave
http://pics.bbzzdd.com/users/xevadex/fixed.jpg

Lemme know what you think. I can't see the terminals of the pot so I drew on top of it my best guesses of where the terminals are and what they should represent.

Does that really fit? Oh... and uhh... although it shouldn't be much of a mistake , C,B,E vertically downward... I think I confused you since you inverted C,B,E.

Wait what. CBE is vertical? That's impossible otherwise they'll be shorted.

Or I meant, from your picture... you wrote CBE, it should be EBC. (Although it could be you found out what's wrong?)

Man it's obvious you're an EE. "It's C-B-E from top view" /sigh..... why would you describe things in an upsidedown fashion.

 

[Ricemarine]

Originally posted by: TuxDave
Man it's obvious you're an EE. "It's C-B-E from top view" /sigh..... why would you describe things in an upsidedown fashion.

:laugh: Whoops .

 

[TuxDave]

So why did you move VCC to Terminal 2 from Terminal 3 on the pot? Terminal 3 should be VCC, terminal 1 should be GND, terminal 2 should be the resistor which goes to the base of the BJT.

 

[So]

Originally posted by: TuxDave

Originally posted by: Ricemarine

Originally posted by: TuxDave

Originally posted by: Ricemarine

Originally posted by: So
http://pics.bbzzdd.com/users/TheJBW/Img_2871.jpg[/L]

Updated
Edit
Where I connected the + terminal for the 9v battery from the top to the middle terminal of the pot changed the voltage to 0.03V.

Originally posted by: TuxDave
http://pics.bbzzdd.com/users/xevadex/fixed.jpg

Lemme know what you think. I can't see the terminals of the pot so I drew on top of it my best guesses of where the terminals are and what they should represent.

Does that really fit? Oh... and uhh... although it shouldn't be much of a mistake , C,B,E vertically downward... I think I confused you since you inverted C,B,E.

Wait what. CBE is vertical? That's impossible otherwise they'll be shorted.

Or I meant, from your picture... you wrote CBE, it should be EBC. (Although it could be you found out what's wrong?)

Man it's obvious you're an EE. "It's C-B-E from top view" /sigh..... why would you describe things in an upsidedown fashion.

It still looks like you have your +9 line and your 20k pot shorted together, instead of the +9 ant the 10k pot (i.e. your +9 looks to be going to the middle terminal instead of the right hand terminal where it should be).

 

[SaturnX]

Originally posted by: TuxDave
So why did you move VCC to Terminal 2 from Terminal 3?

That was going to be my next question... I'm hoping that the OP isn't an EE student, I mean this circuit really shouldn't be causing so much confusion...

 

[Ricemarine]

Originally posted by: TuxDave
So why did you move VCC to Terminal 2 from Terminal 3 on the pot? Terminal 3 should be VCC, terminal 1 should be GND, terminal 2 should be the resistor which goes to the base of the BJT.

Uhh I moved VCC back to terminal 3 the 20k is connected to terminal 2, and then terminal 1 is being grounded. Still not working right. (This is answering So's question too).

 

[TuxDave]

Your ground wiring on the top left popped out? (in your updated picture). Beyond that it looks correct.

 

[So]

Originally posted by: Ricemarine

Originally posted by: TuxDave
So why did you move VCC to Terminal 2 from Terminal 3 on the pot? Terminal 3 should be VCC, terminal 1 should be GND, terminal 2 should be the resistor which goes to the base of the BJT.

Uhh I moved VCC back to terminal 3 the 20k is connected to terminal 2, and then terminal 1 is being grounded. Still not working right. (This is answering So's question too).

well, it looks like you're getting closer.
1. double check that you're on the right row for terminal 2, it looks like terminal 2 is actually in row 6 of your breadboard, not row 5.
2. Make sure the pot is set to something reasonable.
3. Give us your voltages.

and this:

Originally posted by: TuxDave
Your ground wiring on the top left popped out? (in your updated picture). Beyond that it looks correct.

 

[Ricemarine]

Updated picture

[*]V(10k) = 9.11V
[*]V(20k) = 1.95V
[*]V(Transitor drop E to C) = 0.07V
[*]V(Transitor drop C to B) = -0.61V
[*]V(Transitor drop B to E) = 0.69V
[*]Vcc = 9.32V
[*]V(transistor drop E to C w/o pot) = 9.22V

[*]Resistance (between T1 and T2 on pot) = 53.7k ohms
[*]Resistance (between T2 and T3 on pot) = 43.4k ohms
[*]Resistance (between T1 and T3 on pot) = 96.2k ohms

Double checked the wires and ground wire, everything looks ok.

 

[TuxDave]

Voltages look ok, the BJT is on and you're driving it hard so the circuit is working. All you have to do now (if your goal is to get this BJT saturated and get Vce = 5V is to slow tune the pot. Keep monitoring VCE as you adjust it and top when it hits 5V. The resistance between T2 and T3 should be much higher than T1 and T2 in case you're not sure which way to tune.

You know why right?