MAKE: Electronics Ex. 10 Help Needed

[timothy48342]

1)
Do you have a multimeter? Try checking the voltage across the diode. (between H9 and the blue bar. You can stick one multimeter lead in any of the blue bar's holes and the other in F9.)

2)
What capacitor? Where is that attached?

-tim

 

[nyancatvsghosthead]

OMG! I didn't put a capacitor in because it wasn't needed. I don't know why I even

mentioned an electrolytic capacitor because I don't even have or need one. The blue bar

to H9 says 0.004 volts. Or actually that's that LED. I'll check again. I took the LED out

and tried both of them. Should I have done that? It gave me nothing on both of them, so

something could be wrong with the breadboard or the voltage connection/supply wire or

something. I'll try with the LED in right now, hold on. Oh, now it gave me something.

It says 0.010, when I set it to 500v, which is like the smallest one considering that it

would go to such a small decimal. Thanks.

 

[timothy48342]

ok. no capacitor. That's good. You were probably thinking of experiment 8 or 9.

Just to clarify. You now have the switch bypassed? Everything is as before except that you have a wire from C6 to C8? True?

If you have such a low voltage where the diode goes (with the diode in the circuit or not) it seems the transistor is not turning on.

I think we need to know what the transistor is getting to find out why.

Can you check some more with the multimeter?
Check:
Blue bar to Red bar. (make sure we got power)
Blue bar to J3 or to the lead coming out of i3. (Q1 collector)
Blue bar to J4. (Q1 base)
Blue bar to anywhere at the lower lead of Q1. (F5, G5, H5, i5, or J5, to check Q1 emmitter)

--tim

 

[nyancatvsghosthead]

All of these are on 20v setting on Multimeter:

Blue bar to Red bar = 11.98 on 20v

Blue bar to J3 = 11.98 on 20v

Blue bar to J4 = 4.52 on 20v

and Blue bar to F5 = 0.01 on 20v

I see that the biggest difference is that the Blue bar to F5 has such a small voltage.

Could the problem be the emitter? What do you guys think?

-sincerely, nyan cat

 

[timothy48342]

That's some good information nyan cat, but now I'm kinda stumpped.

I would think the fact that the voltage at the base of q1 is 4.52 indicates that the transistor is conducting even if only a little less than a millivolt. But if that were true I think we would see a little more from blue bar to f5.

I'm not sure what that means. Are you sure it is stil hooked up as decribed? Still the same as in the pics except for the switch?

One thing we couldn't quite see in all the pics was the transistor. Could it be in backward? Did it come with a little picture on the packaging showing which lead is the collector and which is the emittor? (the middle is definately the base.)

The book said the transistor should be the 2n2222 or similar. Is that the one your using or something else? (So we can look it up)

To everyone else:
Where else should the voltage be checked to get more info?

Also to everyone else:
If a transistor is connected with the collector and emittor swapped, will it conduct base to collector? And if so what would be the expected base to collector voltage drop?

--tim

 

[nyancatvsghosthead]

It is faced in the right direction, the flat side to the right, ay? Am I wrong? I think that the

book said that the one to the bottom is the emitter and the one in the middle was the

base. Could it be possible that I need to rewire it around the transistor? Please tell me if

this is an absolutely terrible idea. Thanks.

 

[KJ6EAD]

For what it's worth, I built the circuit using a 2N3904 transistor and a yellow high brightness LED and powered it with 12V. With the switch closed and the LED lit the following values were measured: emitter 10V, 12mA; base 10.8V, 150μA; collector 10.2V, 12mA; LED 2V, 12mA. All voltages referenced to ground. Although I arranged the components differently, this is the same circuit as yours. The orange wires are +12V. The bus strip with the black alligator lead is ground and any other colors are connections between components.

 

[nyancatvsghosthead]

So that means that your doing something that I didn't think of. I'm thinking that the

circuit needs a change. What if the emitter thing you said was reversed, and the middle

led is the emitter. Then, I would have been doing it the whole time? Or will that not

matter? I need some advice before I try this idea. Thank you.

 

[timothy48342]

Try reversing it. (If the resistors are still in place as described, then it won't harm anything.) But if you have the flat side to the right, then I think you probably have it right. It would be good to tell us exactly what transistor this is, because there could be some wacky transistor out there that is different from all the rest. (Also, we can verify that is an NPN and not the other one.)
After switching it arround if that doesn't fix things, then just put it right back, so that things don't get confused later.

So what transistor is this?

You have a much lower base voltage than KJ6EAD did and possibly 5 times more base current. (I figured that in a way that is not very reliable.) I don't know what that means, but it would be nice to know for sure.

So... Here is some more points you could check with the multimeter. This will tell us about how current is flowing. If we know the voltage across a resistor and it's resistor value we can get the current flowing through it.

Put the multimeter directly across the leads of each resistor. (As opposed to putting then into the holes in the breadboard.)

And just to verify, since we will need these numbers to do the math...
Is R1 180 ohm? (brown, grey, brown, gold?)
Is R2 10k ohm? (brown, black, orange, gold?)
is R3 680 ohm? (blue, grey, brown, gold?)

And what transistor is this?

-t
edit:KJ6EAD, your photo's didn't get added:endEdit

 

[KJ6EAD]

I had to fight with the editor but now the photos are up there.

 

[timothy48342]

Nice. Like ducks in a row.

KJ, are you neurotic. Do you fold your socks?? (Just kidding.)

Still. A nicely assembled circuit.
-t

 

[KJ6EAD]

Neatness counts when you're trying to make something understandable to others. It also goes a long way in making troubleshooting easier.

I don't fold my socks but I've sometimes numbered the pairs to keep the wear even in cases where I had several identical pairs.

 

[nyancatvsghosthead]

The resistors are all correct. I got the wrong transistor. I don't know what happened.
The packaging said 2n2222 but it gave me 2n6028. Obviously, we all knew that I didn't need 2n6028. There was a packaging flaw. I know this because I checked the text on the transistor. That means that I'm probably doing this perfectly, other than the effing transistor. Stupid manufacturers!

 

[nyancatvsghosthead]

Or does it not matter what the transistor says, because they all say the same thing.

 

[KJ6EAD]

A 2N6028 is a unijunction transistor. It's not an appropriate substitute for a 2N2222. Did you get that at Radio Shack? They have a reputation for such errors.

 

[(*steve*)]

An important lesson for you nyan. ALWAYS check that the component you have is the one you expect to have.

And try not to feel too special. We've all done it.

 

[nyancatvsghosthead]

Where would you recommend buying a new transistor at, so that I don't get the same thing a second time? Would Fry's or Ametron be any good?

 

[jackorocko]

I have bought several transistors at radio shack. Never once got the shaft, but you do need to be careful. Other people are always stuffing the wrong parts back in the wrong bin. It is imperative that you always look at the number on the chip. All radio shack part bags are clear plastic.

I have never been to fry's, but I have heard others say they carry a greater selection then the shack, so it is worth a try.

 

[KJ6EAD]

Fry's carries the NTE brand of components so your 2N2222 would be their NTE123A.

Do you mean the Ametron in Hollywood, CA?

 

[nyancatvsghosthead]

Yes

The Ametron in Hollywood CA. I think it's a lot closer. Will they have it there?
I think Fry's is really far from where I live. You know? Just asking? Do they have it under a different name? If so what is it called? Or would it better if I went to Fry's?