Transistor identifier PART NO. 2212120
The kit consists of a project box containing a small circuit board, 2 pole 6 position switch, transistor
socket, AA batteries, and LED. When a bipolar transistor of JFET is placed in the socket, the switch
is turned through its 6 positions. The LED will light for various switch positions. By comparing the
switch positions where the LED lights and comparing to a chart, the transistor type and pin-out can
be identified. Two lugs on top of the box are provided to measure the voltage drop across the
forward biased junctions which can identify the emitter of the transistor.
Time required: 5 hours depending on experience
Experience Level: Intermediate
Required tools and parts:
Needle nose pliers
Soldering iron
Solder
Screwdrivers
Drill or rotary Tool with drill bits
Six 6-32 x 3/8: screws and nuts
Glue (Loctite GO2 or equivalent) PCB etching solution
Bill of Materials:
Qty
Jameco SKU
Component Name
1
18914
High Class ABS Plastic Speedy Box
1
169279
PCB Blank, single sided
1
2153705
#22 solid wire, assorted colors
1
333973
LED Unicolor Red
1
216081
AA Battery holder
1
445211
Cadmium Lug Terminal
1
112311
IC Socket
1
202287
Knob, 1/4" shaft
1
690769
Resistor, 1/4 watt carbon film
1
2184481
Rotary Switch 6 pole 2 position
Step 1 - Circuit Board Construction
Cut a 2” by 2” one-sided copper circuit board from a larger piece. Measure 1/4“ from each side at
the corners and drill a 5/32“ hole at each corner. With the copper side facing down, measure and
mark 5/8“ from the right side and 1/2” from the top edge. Mark two additional points horizontally to
the left of the first mark and spaced 0.1” (2.5 mm) from the first mark. This will be the location for
the pins of the transistor socket. Keeping the same orientation of the circuit board, measure 1” in
from the right edge and 1/2” from the bottom and mark this point. Measure 0.1” (2.5 mm) horizontally
to the left of this mark and place another mark. This will be the location of the pins for the LED. Drill
1/32 inch holes for each of the 5 locations marked.
Clean the copper side if necessary and using a Sharpie or other etch resist pen sketch the circuit
pattern as shown in Fig. 1 (2X scale) on the copper side of the board. In order to save etchant, it
would be advisable to use the etch resist on portions of the circuit board not connected to the
required circuit pattern.
Step 2 - Project Box Preparation
This step involves the drilling of the top of the project box. The box top measures 5” by 2.5”. As the
box is black in color, it is convenient to tape a piece of paper of those dimensions to the top of the
box. Place the printed circuit board non-foil side up 1/2 inch from the right edge of the box as shown
in the figure. With the board symmetrically placed between the upper and lower edge of the box
top, mark the position of the mounting holes on the paper taped to the box. Following Figure 2,
mark the positions of other holes to be drilled as indicated. Remove the circuit board and using a
rotary tool or file enlarge the holes for the transistor socket and LED so that they will fit through slots
created. Drill the remaining holes.
Step 3 - Assembly of Components
With the project box holes drilled and the circuit board prepared, it is time to mount the components.
First the socket for the transistor must be prepared from the 40 pin socket part # 112311. This is
accomplished by breaking the socket into two parts asymmetrically so that one part does not have
any cross connectors. After the two halves are disconnected, a 3 pin piece is snapped off from the
larger part of the IC socket. This is facilitated by scoring with a utility knife just before the 4th pin
position. Holding the socket with two pliers on each side of the score line, snap the socket to create
a 3 pin and a 17 pin section. The 3 pin section will be used. File off any unevenness in the 3 pin
section. The following pictures illustrate the steps. Feed the pins of the transistor socket through
the top of the circuit board and solder in place. Feed the pins of the LED through the top of the
circuit board so that the cathode pin is oriented to the trace leading to the negative battery terminal
and solder in place. Using 4 6-32 3/8” screws, mount the circuit board to the project box top so that
the transistor socket and LED protrude through the slots previously made. If desired, remove the
part of the center lug projecting from the insulator by bending with a pliers. Mount the terminal to
the box at this time using 1 6-32 3/8” screw.
Solder the wires to the 2 pole 6 position switch before placing the switch into the project box (Note
the jumper wires between the switch lugs). Then solder the leads to the PC board as shown below
(surface mount). Solder the 390 ohm resistor as shown. Put the leads going to the terminal lugs
through the holes provided and solder to the lugs. Glue the battery holder to the bottom of the box
beneath the circuit board and solder the wires to switch and circuit where indicated in the diagram.
Step 4 - Operation of the Transistor Identifier
Taking note of the transistor orientation, insert the pins of the transistor into the socket. Starting
with the switch in the most counter-clockwise position (switch position 1), turn the switch knob
clockwise and note the switch positions at which the LED is lit. Compare the switch positions at
which the LED lights with the identification table. The examples illustrate how to interpret the LED
lighting pattern. Note that the LED will momentarily light when switching from one position to
another because the switch is a make-before-break type.
Bipolar Transistor Identification Table
PIN
CONFIG.
1 2 3
P P N
P N P
P N N
N N P
N P P
N P N
SWITCH POSITION/PIN POLARITY
1/ 1+ 2OFF
ON
ON
OFF
OFF
OFF
2/ 1- 2+
OFF
OFF
OFF
OFF
ON
ON
3/ 2- 3+
OFF
ON
OFF
ON
OFF
OFF
4/ 1+ 3ON
OFF
ON
OFF
OFF
OFF
5/ 2+ 3ON
OFF
OFF
OFF
OFF
ON
6/ 1- 3+
OFF
OFF
OFF
ON
ON
OFF
Example: If the LED is on for switch positions 3 and 6, pin 1 is N type, pin 2 is N type, and pin 3 is
P type. The base is pin 3 and the transistor is NPN. The voltage drop across the terminals on the
top of the project box when the switch is at the LED on positions will be slightly higher for the emitter
to base connection.
JFET Identification Table
PIN
CONFIG.
1 2 3
P N N
N P N
N N P
P N P
P P N
N P P
SWITCH POSITION/PIN POLARITY
1/ 1+ 2ON
OFF
ON
ON
ON
OFF
2/ 1- 2+
OFF
ON
ON
OFF
ON
ON
3/ 2- 3+
ON
OFF
ON
ON
OFF
ON
4/ 1+ 3ON
ON
OFF
ON
ON
OFF
5/ 2+ 3ON
ON
OFF
OFF
ON
ON
6/ 1- 3+
OFF
ON
ON
ON
OFF
ON
Example: If the LED is on for switch positions 2, 4, 5, and 6, the JFET is N channel with the gate at
pin 2. The identification of source pin and drain pin cannot be determined by voltage drop
measurements at the terminals.
LED patterns other than those given in the table indicate a defective transistor.