Circuit Transistor Tester mini SMD Atmega 328

Transistor tester scheme with Atmega mini PCB SMD

The ATmega328p Transistor Tester is a pocket-sized version of the famous component tester developed by Markus Frejek and Karl-Heinz Kübbeler featuring automatic detection of NPN and PNP bipolar transistors, N- and P-channel MOSFETs, JFETs, diodes, double diodes, N- and P-IGBTs, thyristors, triacs, inductors, resistors and capacitors.

Transistor Tester Characteristics with Atmega Mini SMD PCB

  • One-key-operation
  • Three test pins for universal use.
  • Automated detection of NPN, PNP, N- and P-channel MOSFET, JFET, diodes und small thyristors, TRIAC.
  • Automated detection of pin assignment, this means the device-under-test can be connected to the tester in any order.
  • Measurement of hFE and base-emitter-voltage for bipolar junction transistors, also for Darlingtons.
  • Automated detection of protection diodes in bipolar junction transistors and MOSFETs.
  • Bipolar junction transistors are detected as a transistor with a parasitic transistor (NPNp = NPN + parasitic PNP).
  • Up to two resistors will be measured with a resolution down to 0.1 Ohm. The measurement range is up to 50 MOhm (Megaohm). Resistors below 10 Ohm will be measured with the ESR approach and a resolution of 0.01 Ohm. Beware: resolution is not accuracy.
  • Capacitors in the range 35pF (picofarad) to 100mF (millifarad) can be measured with a resolution down to 1 pF (0.01 pF for capacitors with lower capacity than 100 pF).
  • Resistors and capacitors will be displayed with their respective symbol, pin number and value.
  • Up to two diodes will also be displayed with their correctly aligned symbol, pin number and voltage drop.
  • If it’s a single diode, the parasitic capacitance and reverse current will also be measured.
  • Inductances of 0.01 mH to 20 H can be detected and measured.
  • A measurement of ESR (Equivalent Series Resistance) of capacitors greater than 20 nF is built in. The resolution is 0.01 Ohm. For lower capacity values the accuracy of ESR result becomes worse.
  • Vloss of capacitors greater 5 nF is examined. With this, it is possible to estimate its Q-factor.

Please be aware that the test inputs lack a protective circuit, which could potentially lead to inaccurate measurement results. Before connecting the capacitors to the tester, it is crucial to discharge them. Failure to do so may result in damage to the tester even before it is powered on. When attempting to test components that are mounted on a circuit, exercise caution and ensure that the device is disconnected from the power supply, with no remaining voltage.

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Transistor tester scheme with Atmega mini PCB SMD

Transistor Tester Scheme With Atmega Mini Pcb Smd
Transistor Tester Scheme With Atmega Mini Pcb Smd


Testing a Component

  1. Connect the Transistor Tester via the Micro-USB port to a 5V power supply.
  2. Plug the component to be tested into the socket row. Each pin of the component should have its unique socket number (1 to 3).
  3. Press the TEST button and wait for the result shown on the OLED display.


Component Measuring Range
Resistors 100mOhm – 50MOhm
Capacitors 35pF – 100mF
Inductors 0.01mH – 20H
Z-Diodes max 4.5V


Transistor Tester Scheme With Atmega Mini Pcb Smd
Transistor Tester With Atmega Mini Pcb Smd

BOM for assembly of the Tester Transistor with Atmega

Parts Value Description Quantity
C1,C2 100n  SMD Capacitor 0603 2
C3 1n  SMD Resistor 0603 1
C4 47u  SMD Resistor 0603 1
C5,C6 22p  SMD Resistor 0603 2
ICSP-6 ICSP Pin Header Connector 2 × 3 Pins 1
R1 10K  SMD Resistor 0603 1
R2 1,5K  SMD Resistor 0603 1
R3 27k (273)  SMD Resistor 0603 1
R4,R6,R8 680R (681) 1%  SMD Resistor 0603 1
R5,R7,R9 470k (474) 1%  SMD Resistor 0603 1
R10 2k2 (222)  SMD Resistor 0603 1
U1 ATMEGA328P-AU AVR Microcontroller 1
U2 U2 LM4040DYM3-2.5-TR SOT-23 (SOT-23-3) Voltage Reference 1
LED1 Led azul Led 0603 1
OLED OLED Display Oled 128×64 0,96 4 pin 1
Touch switch TEST SW-SMD_4PIN-L12.0-W12.0-H6.0 1
Header TESTPORT Test connector, HDR-6×1/2.54 1
USB Power connector, USB Micro-USB 2 Pins connector 1
X1 8 MHz Crystal Quartz HC-49SMD 1

Firmware Download



Hardware + 3D case


License: CC-BY-SA 3.0

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About the author blog author. Electronics technician for the technical school of Brasilia - Brazil. Interested in electronics, circuits and technology in general.

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