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UPDATE

So even when I remove the switch, the LED is still on (see image below). I.e. there's nothing connected to the base; only to the collector. I'm using the same 2N2222-331 transistor that's in the book (I actually got all my components from the Kit sold separately at http://www.makershed.com/Make_Electronics_Components_Pack_1a_p/mecp1.htm).

I also tried another transistor (of the same type) to make sure that the one I was using wasn't faulty but to no avail.

Is it possible the author messed up the transistor type? In at least 90% of these kinds of cases it's my error an not the author's.

enter image description here


Reading "Make: Electronics". Trying to implement Experiment 10 on Transistor Switching. Diagram shown below: Book diagram

Problem I'm having is that my circuit always has the LED ON when in theory the LED should be off when the button is not pressed because there is no voltage applied to the base of the transistor.

enter image description here

What am I doing wrong here? I'm sure I have the right components (except possibly for the push button) and that I'm using 12V DC. My guess is that I've got the orientation of something wrong but I'm not sure.

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I checkd 2N2222 data sheets from several manufacturers. ALL I found including metal can ones show transistor is CBE readingUP the breadboard as shown. (terminals 48-49-50) SO there is NO DOUBT that they have the circuit VERY WRONG as shown. Their C (terminal 48( goes via R3 to B- (ground). For an NPN transistor it should be B+ / +12v. etc. Build the circuit as I have suggested. It will work ;-). Transistor MAY be dead. –  Russell McMahon Dec 14 '11 at 4:36
    
I emailed them and said their book was broken. They auto-replied their receit. Stay tuned ... . . [I didn't mention who you were or circumstances] –  Russell McMahon Dec 14 '11 at 6:50
    
Great! Will do! –  Tuva Dec 14 '11 at 13:48
    
Wow. Having an introductory book like that showing incorrect information is really bad. Curious but otherwise "unhooked" people could get frustrated and give up, never to come back. –  darron Dec 14 '11 at 17:06
1  
Personally I'm not deterred at all. This was a great learning experience. I'm sure I'll have a lot more frustrations from manufacturers along the way... :-). –  Tuva Dec 14 '11 at 20:56
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2 Answers 2

up vote 13 down vote accepted

Very nice presentation of your problem. Well done, and thanks.


(1) Check that your switch connects left to right when pressed and not top to bottom.
Remove switch - does LED go out.
Use a piece of wire. Does LED turn on?


(2) It appears that the problem is that the circuit they have given you is utterly and completely and inexplicably scrambled. It would be hard to have the circuit much wronger that that and still light the LED! It just MAY be sort of correct given several unlikely assumptions.

How can this be?
I so didn't believe what I was seeing that I checked several times.

2N2222 data sheet here

enter image description here

What transistor are YOU using? What is the pinout.

Even if YOU are not using a 2N2222 they should be.

The circuit is wrong because:

  • They say 2n2222 so it should be NPN

    It is normal to put the LED in the collector circuit but not essential.

    If R3 is in collector then it should not go to V- power rail but to V+.

    If we assume LED is in Emitter circuit then R1 must be in collector circuit and the transistor is being used as an "emitter follower". Not what you would usually do or for a beginner but say that's correct. And the pinout is backwards. Let's assume it is.

    Then base should be being pulled +ve to turn on. It is.

    They should have a pulldown on the bas to ground to turnthe transistor off - especially when used as an emitter follower. Connect another 10k from SW1/R1 junction to ground. Test . report.

BUT

Ensure transistor is CBE bottom to top as per 2N2222 datasheet or find what it really is.

  • Identify C B E with certainty. Ensure NPN transistor.

  • Collector via R3 and LED to V+

  • Emitter to ground

  • 10K from Base to ground

  • 10K via switch to V+

Like this with different values, but I have added extra 10k from base to ground (a wise precaution).

enter image description here


I checkd 2N2222 data sheets from several manufacturers. ALL I found including metal can ones show transistor is CBE readingUP the breadboard as shown. (terminals 48-49-50) SO there is NO DOUBT that they have the circuit VERY WRONG as shown. Their C (terminal 48( goes via R3 to B- (ground). For an NPN transistor it should be B+ / +12v. etc. Build the circuit as I have suggested. It will work ;-). Transistor MAY be dead.

Datasheets

metal can

[TO18 & TO39 metal can both the same](metal can )

All TO92 plastic seem to be ONSemi - several distributors:

Did they provide a proper circuit diagram?
If so please show it.

ONSemi TO92 plastic


Update:

Here is the book concerned .

(1) The transistor is reversed. Turn it around 180 degrees and their circuit is as they intended. Their basic data shows the transistor wrongly.

(2) And / But - the circuit is an emittee follower as it was obvious it would be if you "just" reversed the transistor. This is such an 'interesting' way to do things that it was hard to believe that it was intended. It was.

enter image description here

Their "rather interesting" circuit:

enter image description here

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Thanks for the update! I tried and it works. Sorry I forgot to include the circuit diagram. –  Tuva Dec 16 '11 at 3:47
    
On the 2N3904, isn't the order EBC? I know the circuit in question uses a 2N2222, but I just built a breadboarded circuit the other day that used a 2N3904 and EBC worked fine. –  insta Oct 17 '12 at 15:40
    
RussellMcMahon, you have some links that use the IP address of the host. Links die on the internet, direct IP links die even more often, can you please update these to be non-ip links? –  Kortuk Oct 17 '12 at 18:02
    
The "man with no name" downvoter strikes again - 9 months after yhe action. Marvellous stuff. +9/-1 - if you do not think this is useful then you may wish to explain why so that we can point out what it is that you need to know more about. –  Russell McMahon Oct 20 '12 at 3:40
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It's likely your transistor base acts like an antenna; so you should put a resistor from base to ground (-). This is for when you open the circuit on the base of transistor, the base is pulled down by that resistor to ground potential.

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