(G3TR) Transistor’s Type Recognizer


Recycling ! – New life for old computer parts – Old computer boards are populated with a lot of SMDs working devices like diodes, bjt, mosfet etc. Desoldering and testing it you may have a little treasure to be used in new prototipes or experimental boards. Let focalize our attention to the transistors part. Often the problem is to recognize the transistor’s type, because of SMD marking code. In any case, a circuit that can test such device allows to save money, recycling them in experimental boards. The circuit here described is a my original Idea and  use an AVR microcontroller to test and automatically show the tipology of the transistor under test, obviously if it is still working. Inserting an unknown transistor ( smd or not , low power or high power) the circuit is able to displays:

  • NPN
  • PNP
  • N- CHANNEL MOSFET
  • P- CHANNEL MOSFET

if the device is good, or:

  • SHORT
  • BROKEN

according to the case, if the device is no more working.

The circuit is able to test diodes too.

The G3TR board shows the test result on a two line character display as well as on a terminal attached to the RS232 interface. On Linux the ‘putty’ terminal works very fine.The working principle is explained with the following tables.Please refer to the attached diagram at the end of this article.

NPN:

OUT A OUTB OUTC IN RED GREEN YELLOW
H L L H off off off
H H L H on off off

PNP:

OUT A OUTB OUTC IN RED GREEN YELLOW
L H H L off off on
L L H L on off on

N-CHANNEL MOSFET:

OUT A OUTB OUTC IN RED GREEN YELLOW
H L L H off off off
H H L L on off on

P-CHANNEL MOSFET:

OUT A OUTB OUTC IN RED GREEN YELLOW
L H H L off off on
L L H L on on off

DIODE anode on TP3:

OUT A OUTB OUTC IN RED GREEN YELLOW
H X L X on off X
L X H X off off X

DIODE anode on TP2:

OUT A OUTB OUTC IN RED GREEN YELLOW
L X H X off on X
H X L X off off X

Prototipe screen after reset:

The screen below shows the results of four measures:

G3TR schematic