Introduction: Simple Transistor Tester

Picture of Simple Transistor Tester

Hello hello ladies and gentlemen. like many of you I love to experiment with electronics. I love prototyping on a bread board as well as salvaging parts from pre - existing circuits. And like most people I tend to be forgetful and a trifle disorganized. This often leads to me having a small pile of discreet components on my work bench. The main component being transistors.
I made this simple circuit as a way to remedy that issues as well as a way to test and identify the pin out of most transistors.

Step 1: The Materials

Picture of The Materials

The materials you will need for this project are:

-A CR2032 battery holder
-2 LEDs
-4 1k resistors
-8 breakable female pin headers
-A switch
-A bit of perf board

Step 2: The Tools

Picture of The Tools

The tools you will need are:
-A set of wire clippers
-A sharp knife
-A bit of routing wire
-A pen
-A soldering iron
-Some solder

Step 3: The Circuit

Picture of The Circuit

The circuit is designed to be able to sort between both NPN and PNP transistors. In both the EBC and BCE configurations. (I am no computer please excuse the circuit. it is Cain Aided Design)

Step 4: Preparing the Board

Picture of Preparing the Board

I accomplished this by using the bw
attery clip as the thickest part of the circuit and scoring the board with the knife. All before snapping the board along the score using the table for suport.

Step 5: Adding Power

Picture of Adding Power

Attach the battery clip to the end of the board and attach the switch near the positive termanal. Join the two together and attach the center pin of the switch with some routing wire for a path for power.

Step 6: Adding the Sockets

Picture of Adding the Sockets

place the two rows of female pin headers a small distance from the battery make sure to maintain ample distance from the battery to accommodate the other components. While maintaining ample space for the labels to be added later. Note it can be very troublesome seating the headers at first but once the first pin is joined the rest are a snap.

Step 7: Attach the LEDs and Resistors

Picture of Attach the LEDs and Resistors

place the resistors and LEDs according to the schmatic. A resistor on each base. One LED goes to the collector of the NPN via the cathode. And one LED goes to the PNPs emitter via the anode. try to keep the LEDs in line and do not forget the resistor on the positive termanal of the LED. (I was reminded of this heavily by the community and my peers~)

Step 8: Finish Routing

Picture of Finish Routing

Finish routing by connecting collector of the PNP to positive. Connect both of the PNP's emitters. Connect both of the NPN's emitters together and connect that to ground. Connect the resistor and the cathode of the LED comming from the PNP transistor to ground.

Step 9: Add the Labels

Picture of Add the Labels

Create the lables and clearly mark EBCE closes to the corresponding point and mark which transistor the port is testing.

Step 10: Finaly Add the Battery and Test~

Picture of Finaly Add the Battery and Test~

Place the battery in the clip according to polarity. take your sample transistor and hold it in the headers. depending on your transistors gain you could end up triggering both the NPN and the PNP side. In this case the brightest response will indicate the proper type and orientation. Any responses on how to remedy this would be greatly appreciated. This tester can be used on most BPJ transistors though I have not tried and form of FET.

Thank you and have a pleasant day.


Abhi909 (author)2016-01-31

great project

can i place your project on my website.

i'm working on a website which is related to electrical projects.

i also mention your name.

plz reply

cainvsc (author)Abhi9092016-01-31

I think that sounds like an excellent idea. You can feel free to use any of my ibles so long as credit is given. Would you mind posting a link when you have your website up and running?

Funktioniert (author)2015-09-11

next time i Power my solder Station i want to bulid this little tester and optimise it for my tests with an led test. thanks for share :)

i hope you understand my Comment....

cainvsc (author)Funktioniert2015-09-11

I believe I do. But what do you mean by LED test?

Funktioniert (author)cainvsc2015-09-12

I use a Lot of rgb led and to Check them if they okay i have to connect every Pin an 1 resistor. so i want to bulid 2x3 Sockets with 4 Pins so i can Stick the led throu it an Check if r g and B Light up.
i Post the next time an chematic and the finish Tester.

cainvsc (author)Funktioniert2015-09-12

It sounds intresting I can't wait to see the ible

Funktioniert (author)cainvsc2015-09-14

it's finish :D
from the left side (top view):
npn test
pnp test
led rgb common +
led rgb common -
i Made it for 12v DC so i use 1k Ohm resistors to go on 3V and 9mA for the LEDs. it's ok to Check if they work or not.
on top is a + rail on the bottom a - rail.
so I maybe want to do more Tester i plannend input and Output.

cainvsc (author)Funktioniert2015-09-29

That's a very clean and we'll thought out wiring plan. good work.

pfred2 (author)2015-09-12

I like scratch built circuits but I have built a couple AVR TransistorTester kits now, and I do have to say that they are brilliant. If you are really into electronics then you owe it to yourself to get one of these kits, and make it. I am only posting this link because it is the cheapest kit I have seen. It is not quite the best, but it is still pretty good

The best one is the graphical kit. But it is like $20, or so. The 2x16 is just as accurate, but not quite as visually appealing. After I built a 2x16 and saw the GUI tester I had to get one for myself.

It is in my opinion the ultimate AVR TransistorTester. Both have the precision voltage reference, not just a zener diode. That makes them more better than some other AVR testers out there. Although I have a zener tester too, and it really isn't that terrible. The zener reference testers you can get really cheap. I think I have seen them for like $8 assembled.

markschilke (author)2015-09-11

Great write-up, Cain!

The NPN circuit makes sense to me, but the PNP circuit seems to be an example of the low-gain "reverse active" operating mode. (See the information at the

website.) Did you intend to swap the PNP collector and emitter so that the base-collector current biases the transistor on to allow emitter current to flow?


cainvsc (author)markschilke2015-09-11

I must confess that's a bit more in depth then my knowledge of PNP transistors goes. Personally iv only really ever had a PNP in that configuration. how could I have improved this circuit?

markschilke (author)cainvsc2015-09-11

On the NPN side of the tester schematic, you've got the emitter pins connected to the negative of the battery, the base pin connected through its resistor to the positive of the battery, and the collector pin connected through the LED & resistor series combination also to the positive of the battery.

For the PNP side of the tester, it would probably be better to connect the emitter pins to the positive of the battery, the base pin through its resistor to the negative of the battery, and the collector pin connected through the LED & resistor series combination also to the negative of the battery. Kind of like this:

enter image description here

In the above sketch, connecting the free end of resistor R1 ("Commande") to the negative of the battery will cause the LED to light up.

You mentioned in Step 10 that sometimes both the NPN and PNP sides get triggered. The LED & resistor on the side not being tested should be an open circuit and therefore zero current will flow. From what you wrote, there might be a wiring error (such as a solder bridge, perhaps) sneak path that allows the reverse active mode on the PNP side to conduct more than it usually would.

cainvsc (author)markschilke2015-09-12

In step 10 I ment to say an test will have a positive response on both side. It'll register as both pnp and npn

markschilke (author)cainvsc2015-09-12

Each side (NPN or PNP) of the tester should be completely independent of the other. If the "wrong" LED is lighting up with only one transistor plugged in, then somehow there's a cross feed. You might try confirming that it's not just static by connecting a meter that can measure DC milliamps in between the LED and its resistor.

cainvsc (author)markschilke2015-09-12

What I mean to says is that once I test a npn on the pnp side the pnp led can often be illuminated on the pnp side as it the npn transistor was a pnp transistor. If that makes it any clearer. I do apologize for the confusion.

bobbyfixit (author)2015-09-11

AND 2 U 2

nwonharp (author)2015-09-11

Thanks for the project ! I built a transistor tester a long time ago using a simple oscillator circuit . Using a PNP and NPN transistor , with sockets . I could substitute the transistor in question into the socket . Here is basically the circuit :

If it oscillates , then the transistor is working . Basically a dynamic test .

Cheers , take care , and have a good day !!.......73

cainvsc (author)nwonharp2015-09-11

That's so smart~ I never would have though of doing it like that.

nwonharp (author)cainvsc2015-09-11

I can't take all of the credit for it , it is an old circuit . It works with most any general - purpose NPN or PNP transistors . Over the years , I have built several testers ( mostly because I needed them to do my job ) that are as accurate as the ready -made ones that you can buy . A 4-20 mA calibrator , SCR tester , and other things . When I retired , the guys that I worked with insisted that I leave them there so they could use them , rather than take them home . They were all pretty simple circuits , but they WORKED ! Keep working with electronics , maybe even build an oscillator circuit like the one in my other post , and share it with everyone .

Cheers , take care , and have a good day !....73

dmwatkins (author)2015-09-10

Very nice!

Joytabarsi (author)2015-09-10

the. question marks were emojis

cainvsc (author)Joytabarsi2015-09-10

Question marks?

cainvsc (author)2015-09-10

In hindsight a lower resistance resistor probably should have been used as opposed to the 1k in line with the LEDs

About This Instructable




Bio: My name is Alex Rivera. Though I prefer to be called cain. I am a high school student in South Carolina. My greatest passion in ... More »
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