Picture of Transistor Tester
Transistor Tester.png

The purpose of this circuit is to test NPN and PNP transistors and to identify their pin layouts, ie ECB, EBC. I find myself testing a lot of transistors to determine their pin layout and type and as such find that building the test circuit on a breadboard has become a hassle so I wanted an easy circuit that would be more permanent and would allow me to test transistors.

The transistor type NPN/PNP determines the polarity of the connections. The orientation of the transistor is the pin layout. I define the pin layout when looking at the top of the transistor with the flat side facing toward you. That is probably not the official way to classify them but it makes more sense to me when I am placing them in a circuit.

- EBC stands for Emitter Base Collector. When I use this acronym I am saying that the pin to the left is the emitter, the middle pin is the base, and the right pin is the collector.

- ECB similar to the above acronym stands for Emitter Collector Base. The emitter pin is again on the left but the middle pin is the collector and the right pin is the base.

I have gone through about 100 transistors that were pulled from old electronics and have never found any other orientations so i have found that there is no need to test for anything but these two orientations.

MROHM6 months ago

Simple But So Useful..Many Thanks!!!!!

hakuna matata7 months ago
IC 1 is for PNP transistor and to work out the format the left side of the IC is to determine if it is EBC while the right side is to determine ECB am I correct please let me know same for IC 2 for NPN left side is EBC and the right side is ECB correct????
dudes1 year ago
could u provide a full schematic? I'm having trouble understanding where everything goes. thanks
LeumasYrrep (author)  dudes1 year ago

Here you go! Let me know if there are any errors, I just threw it together today.

Transistor Tester.png
A note- it's bad habit, electronically speaking, to call ground negative and high positive, since high can be at 0V or less and ground can actually be at a negative voltage, though in most cases it's irrelevant, but it's still a good thing to remember.
Nice circuit but without the schematic diagram, it will be hard to follow on the instructions, if you have the schematic diagram I will be grateful if you publish it.Nothing like the schematic diagram for electronic; I learned electronics many years ago and always used schematic for any electronics projects
Hope this helps and that the sketh goes through
LeumasYrrep (author)  elfarandulero3 years ago
The into step has the schematic. There are only two circuits that are very basic but the layout of the pins is what creates 4 different circuits for this tester.
What is the "into step"? and where is the link for it?
LeumasYrrep (author)  elfarandulero3 years ago
*intro step. It is the very first page, second picture.
floxin3 years ago
There is a wide variety of simple bipolar transistors. When I go to buy some, the salesperson usually asks: plastic or metal even for such an elementary device as the "workhorse" 2N2222.
Google "Mouser Electronics", a well known electronics distributor. Go left to "Product Finder". Click on "Discrete Semiconductors" and then click on "Transistors Bipolar" and "Show Products". Select page 4 and look at left images 13 and 14 from top. The 6th column from left says "Data Sheet" (click to open)and you will see a TO 92 package (plastic) and TO 39 package (metal) respectively. Kind of confusing. The article deals only with plastic packages. When it comes to metal (TO39), my rule of thumb is that the lead physically closest to the metal tab is the Emmiter but I am not sure that this is always true.
floxin3 years ago
it is easy to add stuff when others have done the hard work. I respectfully submit the following comments (in several messages).
1) There is a standard numbering system for IC sockets that avoids any possible confusion. It is based on the half circle notch (indent) in the plastic frame seen pointing downwards on the parts picture (shown under Step 1). (A) Place the socket in front of you so that the slots will be in two horizontal parallel rows. (B) Orient the socket so that the half circle notch is at your left. (C).Starting from the left on the lower row, the slots are 1, 2, 3, ...x. When you reach the end of the lower row, jump counter clock wise to the top row and continue numbering x+1, x+2,.. to the end. If you have to insert an IC, look at its top surface and you will see a tiny embossed circle (ususally) or some other mark. That mark must point the same way as the half circle notch.
Hi !

Okay, ive stumbled upon a problem, i've only just started learning electronics and finding it extremely difficult !

But i'm tring to follow the exact specs as this transistor tester as to avoid any mistakes but im cnow confused to heck and back !

Problem 1:
- Very Early-on, the diagram showing the simple schematic of the NPN Transistor tester circuit shows the BASE of the NPN being connected to the 10K resistor but in all the photo's the BASE of the NPN transistor (bottom-right test circuit on prototype-board looking at it from non-solder-side!) is connected to the 470 OHM Resistor.
PLEASE please please can anyone confirm why this is ?

Problem 2:
On the same circuit (bottom-right test circuit on prototype-board looking at it from non-solder-side!) the LED's 'Notch' {meaning the Cathode} is facing upwards... No matter how i orient the LED on my setup {using the same components, no substitutes!} instructions say 'Make sure the Anode is connected to the resistor' but how can this be possible for the LED's Notch facing up ? I really cant make head-nor-tail of this...

Please help as this is an excellent learner project for me and i have many transistors to test, lol, but go easy on me, Learner-Here, lol x2!

Many thanks in advance for the help with what will seem like child's-play to you folk, but rocket-science to me !
LeumasYrrep (author)  offtherails20103 years ago
I think I have a solution for you:

Problem 1:
From the simple test schematic I have the base of all the transistors are connected to the 10K resistor. In this schematic the base pin is always drawn as the middle of the three transistor pins. No when we go to real life components the pin layout is not the same. For the bottom right transistor the pin layout from left to right is; Emitter, Collector, Base. So the base moves from the middle pin to the right pin.

Problem 2:
The picture in step 6 appears to be playing tricks on my eyes. It looks like the bottom right LED has a flat facing up. I am sure this is not the case. Just make sure to place you LED with the correct polarity. I like to use a button cell to quickly check the polarity of LEDs before placing them, I never trust the makings on any of the LEDs I pull from old electronics.
Many many thanks for the extremely appreciated help as i really need to make this tester circuit especially as it uses very simple components for a complete noob like me, i am so very grateful for the extra help!!!

Obviously your circuit works as others have made it too and even made some changes but because ive only just started learning electronics this year its playing havoc with my old brain trying to learn new tricks, lol !

I'll be resuming this project over the weekend and am quite determined to make an enclosure for it as well because of the great practical use of this very important circuit !!!

Once again many thanks for your kind patience with assisting a complete noob and making it a few good steps closer for me to make this awesome circuit !!!

Many many Thanks for a truly amazing set of instructions - nice high res pics and simple enough for me to start making as ive got a bunch of transistors that i dont know if they work or not !!!

Also i have a bunch of rechargeable LIR 2032 Coin Cells to finally start making use of them !!

Thanks so much and Keep making your instructables with extremely outstanding high-res pictures !!! (2mb per pic - nicely done !!!)

!!! "A Simple Yet VERY Effective Piece of Work" !!!
slangtom3 years ago
thank u for an insightful upload. May i know how can I use a PIC micro controller to test a BJT Transistor. This is a project i am currently working on in School, but i am finding it hard to understand how the PIC will be able to detect the state of the transistor (ie if its NPN or PNP). Also what mechanism will it employ in the test and using what theory.
LeumasYrrep (author)  slangtom3 years ago
It was my original hope that I could use a micro-controller, the Arduino, to be able to do what you are describing. I was going to use a LCD display that would tell me the pin layout and type of transistor but I ran into problems. First I wanted all transistors to be tested in a single socket but in placing all the circuitry "overlapping" to that socket I was getting false readings even before placing the test transistor. Also the only was for the micro controller to detect the test transistor I would need transistors to connect into the Arduino and strange things started to happen whey you are testing one transistor but have a few more further into the test circuit.

Long story short I was never able to figure out how to make this method work. I am not sure if it is even possible to do but my simple understanding of circuity prevented me from going any further.
jensenr303 years ago
Hi. Ryan here. I have to say that this instructable is great!
It's well written and very easy to follow.

I made a transistor tester that uses four socket pins to test both EBC and ECB.
the leftmost three pins (see pic) test transistors to see if they are EBC. To test your transistors to see if they are ECB, simply rotate the transistor 180 degrees and move the transistor to the rightmost pins (see pic).
I would have used a battery almost identical to yours, but I didn't have any button cells that weren't dead.

That is my version of your transistor tester!  XD

OH! And I almost forgot. I put feet on the bottom. They are made of superglue (ghetto as hell) and they work really nicely. see pic

LeumasYrrep (author)  jensenr303 years ago
Very nice. I like how you have reduced the number of components by doubling up the test sockets. Thanks for the pictures.
no prob. I like sharing my better ideas (and hiding the bad ones! lol!)
please give me this video
mrmerino3 years ago
I wonder if you could "float" the back of the board on some sort of liquid latex, so you'll have a nice nonconductive place to put your hand. Or just screw it to a piece of wood.
profpat3 years ago
this a great instructable! will build one for myself! thanks for sharing!
LeumasYrrep (author)  profpat3 years ago
how much it will cost all together??????? & COULD U GIVE A Brief description about it. like in which store i ll get the meterial etc.i like it its really nice!!!!

Nice instructable I will build one myself. But I also have a suggestion, try making a project box for it.
A box is a little extreme for a project like this. Nailing it to a scrap piece of wood might be nice though.
LeumasYrrep (author)  project_builder3 years ago
I had initially considered a project box. I love wood working so I was going to design my own enclosure but I desided aginst any kind of box.

First the circut would have to be altered, the IC sockets would need to be on a separate smaller board so that I could place then on the underside of the box lid while having them stick out of cut outs through the top. I have tactile switches with longer buttons so I could leave them as they are and build some wooden pegs on the box lid to press them. Also the LEDs would need to be extended.

By skiping an enclosure I was able to simplify the circuit and keep the tester in as small a package as I could solder. I have these flat plastic organizers that I place all my components in and as an added bonus this tester is just small enough to fit in one of the compartments next to my transistors.
Do a nice box with a lid. Open the lid shows the top of the board. Board being recessed in the bottom half of the box, close the lid. Might be very nice kind of box that looks good enough to place on display.
This is honestly a project that I think goes better without a box... A project box'd just get in the way whenever you want to swap out the transistors.

That being said, I'd like to see one for Flame Emitting *ahem* ... I mean, Field Effect Transistors... slip of the metaphorical tongue...
GonzoDuke3 years ago
Thanks for the project! Did mine on a piece of strip board I had on hand.
LeumasYrrep (author)  GonzoDuke3 years ago
Great! Thanks for posting a picture.
mrmerino3 years ago
Boy, I wish I'd had this when I built the Tillman preamplifier. Wait, does this work on fets?
i dont think this will work for fets, fets has a different type of biasing!
Brosiman3 years ago
Is it me or did you make a mistake with your acronyms? :

"- ECB stands for Emitter Collector Base. When I use this acronym I am saying that the pin to the left is the emitter, the middle pin is the base, and the right pin is the collector.

- EBC similar to the above acronym stands for Emitter Base Collector. The emitter pin is again on the left but the middle pin is the collector and the right pin is the base. "

But a great project!
LeumasYrrep (author)  Brosiman3 years ago
Great catch! I must have switch the acronyms while typing. Thanks for pointing it out I will fix that right away.
Yep, it is backwards
codyg1023 years ago
Great job! Well documented, lots of pics. Thanks for sharing it.