Transistor Identify and Test


2007 / 08 / 18

This is a prototype,  only transistor identify and test are implemented now. 


2007 / 08 / 18

I am trying to design a small tester to tell me, "what the three ends component is ?" and "Is it good? "...., Of course, a multimeter can do this, but cost time. When deal with SMD transistor, my trembling fingers and reading glasses seem helpless.......

This is part of the design, the FET identify circuit is more complex and not implemented yet.

So, here is the idea, ......

If it's a transistor, then is it PNP or NPN, which end is Base, Collect... and so on.

Since there are only 12 tyes of transistors layout (NPN, PNP * CBE, BCE, ...), each type has a typical V-read when manipulating Vdd and Vbias.

In this design, I use PIC16F88 to do all the jobs, It's AN1~AN3 act as analog input, and floating/ high/low output. via 47k resistor to provide Vbias.

RA4,6,7 as Vdd / GND/ floating. sw1 is no function now.

The transistor pattern I use are,  when  Vdd = +/- 5 V to GND,

when Vbais = GND,  Vread < 0.1 *Vdd

when Vbais = floating,  Vread < 0.1 *Vdd

when Vbais = Vdd,  Vread > 0.1 *Vdd

when Vbais = floating,  Vread < 0.1 *Vdd

ALL above are in sequence, all must true.

Load resistors are 330 Ohm each, bias resistor is 47k Ohm.


(Click above figure for large picture)

Just power on and plug a transistor, this tester will check if there is short circuit in the transistor, if yes, point out the leads.

This design can identify a transistor and it's layout within milliseconds. I use 0.5 second delay- time to make it more easy to read.

Here is the power on display, and read out display.

CBE =132 means the lead correspond to the socket pin.

Since it's prototype, It didn't display beta value of the transistor, but Vread.

D = 125 means when Vbias is same as Vdd, the Vread= (Vdd / 255 * 125) , In this case it's 2.45V and drain current is (2.45 V /330 ohm) =7.4mA

L = 0 means when Vbias is same as GND, the Vread= (Vdd / 255 * 0) , In this case it's 0 V, not detectable leaking current.


Source code will NOT open this time. Don't ask.


Express SCH file                  PIC16F88 HEX code




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Philip Sun / TAIWAN

copy right 2004