Circuit transistor tester M328

Circuit transistor tester M328 capacitor test

Transistor Tester M328, with ATmega328 microcontroller, LCD-Display 128×64, measures resistor, inductor, capacitor, capacitor ESR, NPN and PNP bipolar transistors, N- and P-Channel MOSFETs, JFETs, diodes, double diodes, N-IGBT and P-IGBT, Thyristors and Triacs.

Schematic transistor tester M328

Schematic M328 Transistor Tester

Features circuit transistor tester M328

  • Automatic detection of NPN and PNP bipolar transistors, N- and P-Channel MOSFETs, JFETs, diodes, double diodes, N- and P-IGBTs, Thyristors and Triacs. For Thyristors and Triacs the ignition current and holding current must be reached with the tester. For IGBTs the 5V signal should be enough for driving the gate voltage.
  • Automatic detection of pin layout of the detected part.
  • Measuring of current amplification factor and Base-Emitter threshold voltage of bipolar transistors.
  • Darlington transistors can be identified by the threshold voltage and high current amplification factor.
  • Detection of the protection diode of bipolar transistors and MOSFETs.
  • Measuring of the Gate threshold voltage, the Gate capacity value and the RDSon at almost 5V gate voltage of MOSFETs.
  • Up to two Resistors are measured and shown with symbols and values with up to four decimal digits in the right dimension. All symbols are surrounded by the probe numbers of the Tester (1-3). So Potentiometer can also be measured. If the Potentiometer is adjusted to one of its ends, the Tester cannot differ the middle pin and the end pin.
  • Resolution of resistor measurement is now up to 0.01 Ω, values up to 50M Ω are detected
  • One capacitor can be detected and measured. It is shown with symbol and value with up to four decimal digits in the right dimension. The value can be from 25pF (8M Hz clock, 50pF @1M Hz clock) to 100mF. The resolution can be up to 1pF (@8M Hz clock)
  • For capacitors with a capacity value above 20nF, the Equivalent Serial Resistance (ESR) is measured with a resolution of 0.01 Ω and is shown with two significant decimal digits. This feature is only available for ATmega with at least 16K flash memory.
  • For capacitors with a capacity value above 5000pF, the voltage loss after a load pulse can be determined. The voltage loss gives a hint of the quality factor of the capacitor.
  • Up to two diodes are shown with symbol or symbol in correct order. Additionally, the flux voltages are shown.
  • LED is detected as diode, the flux voltage is much higher than normal. Two-in-one LEDs also detected as two diodes.
  • Zener-Diodes can be detected, if reverse break down Voltage is below 4.5V. These are shown as two diodes, you can identify this part only by the voltages. The outer probe numbers, which surround the diode symbols, are identical in this case. You can identify the real Anode of the diode only by the one with breakdown (threshold) Voltage nearby 700mV!
  • If more than 3 diode type parts are detected, the number of founded diodes is shown additionally to the fail message. This can only happen, if Diodes are attached to all three probes and at least one is a Z-Diode. In this case, you should only connect two probes and start measurement again, one after the other.
  • Measurement of the capacity value of a single diode in reverse direction. Bipolar Transistors can also be analyzed, if you connect the Base and only one of Collector or Emitter. If an ATmega with more than 8K flash memory is used, also the reverse current of the diode is measured with a resolution of 2nA. The value is only output to the screen if it exceeds zero.
  • Only one measurement is needed to find out the connections of a bridge rectifier.
  • Capacitors with value below 25pF are usually not detected, but can be measured together with a parallel diode or a parallel capacitor with at least 25pF. In this case, you must subtract the capacity value of the parallel connected part. For processors with at least 32K flash memory the tester changeover to a special capacity meter function, if a capacitor with more than 25pF is once measured at TP1 and TP3. In this capacitor meter mode, you can measure capacitors below 25pF at TP1 and TP3 directly.
  • For resistors below 2100 Ω also the measurement of inductance will be done, if your ATmega has at least 16K flash memory. For that, an inductor icon is shown behind the resistor
    icon. The range will be from about 0.01mH to more than 20H, but the accuracy is not good. The measurement result is only shown with a single component connected.
  • Testing time is about two seconds, only capacity or inductance measurement can cause a longer period.
  • Software can be configured to enable a series of measurements before power will be shut down.
  • Build in self test function with an optional 50Hz Frequency generator to check the accuracy of clock frequency and wait calls (only for processors with at least 32K flash memory).
  • Selectable facility to calibrate the internal port resistance of port output and the zero offset of capacity measurement with the self test (only for processors with at least 16K flash memory). An external capacitor with a value between 100nF and 20μF connected to pin 1 and pin 3 is necessary to compensate for the offset voltage of the analog comparator. This can reduce measurement errors of capacitors of up to 40μF. With the same capacitor, a correction voltage to the internal reference voltage is found to adjust the gain for ADC measuring with the internal reference.
  • Display the Collector cutoff current ICE0 with currentless base (1μA units) and Collector residual current ICES with base hold to emitter level (only for processors with at least 16K flash). These values are only shown, if they are not zero (especially for Germanium transistors).
  • With the dialog function, you can use a frequency measurement at port PD4 of the ATmega. The resolution is 1Hz for input frequencies above 25kHz. For lower frequencies, the resolution can be up to 0.001mHz by measuring the mean period. You should read the subsection Frequency measurement 2.2.4 at page 13 for details of connection of a frequency signal.

Attention: Always be sure to discharge capacitors before connecting them to the Tester! The Tester may be damaged before you have switched it on. There is only a little protection at the ATmega ports. Extra caution is required if you try to test components mounted in a circuit. In either case, the equipment should be disconnected from the power source, and you should be sure, that no residual voltage remains in the equipment.

Circuit Transistor Tester M328 Led Test

Bom Circuit transistor tester, M328

Name Designator Footprint Quantity
Resistors 1/4W
680R R1,R3,R5 Blue, gray, black, black, brown 3
470k R2,R4,R6 Yellow, violet, black, orange, brown 3
33k R8 Orange, orange, black, red, brown 1
3k3 R9,R13 Orange, orange, black, brown, brown 2
100k R11 Black, black, black, orange, brown 1
10k R12,R7,R23,R26,R27,R28 Brown, black, black, red, brown 6
220R R14 Red, red, black, black, brown 1
27k R15,R10 Yellow, violet, black, red, brown 2
2k2 R17 Red, red, black, brown, brown 1
1k R24,R25 Brown, black, black, brown, brown 2
ATMEGA328P U1 Microchip AVR microcontroller 1
HT7550-1 U2 100mA Low Power LDO 5V 1
TL431 U3 Three-terminal adjustable shunt regulator 1
LED LED1 Led 3 mm red 1
BC557 Q1 PNP transistor 1
BC547 Q2,Q3 NPN transistor 2
100nF C11,C3,C6,C7,C10 Ceramic capacitor 5
10uF C8,C5 Electrolytic capacitor 2
22pF C1,C2 Ceramic capacitor 2
10nF C4 Ceramic capacitor 1
1nF C9 Ceramic capacitor 1
1206 REF1,REF2 Ceramic capacitor 1206 (Optional instead C8,C5) 2
SOCKET_TFXTOOL ZIF1 ZIF connector dip 14 1
ENCODER SW1 Rotary Encoder 1
TP1 P1 HDR-1×1/2.54 1
TP2 P2 HDR-1×1/2.54 1
TP3 P3 HDR-1×1/2.54 1
BAT+ P4 HDR-1×1/2.54 1
BAT- P5 HDR-1×1/2.54 1
F_IN P6 HDR-1×1/2.54 1
GND P7 HDR-1×1/2.54 1
8M X1 HC49S – Crystal Cristal 8 MHz 1
JLX12864G-378_SHORT LCD1 LCD display JLX12864G-378 1
Download files for Circuit transistor tester M328, PCB in Gerber, PNG, PDF, SVG




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Datasheet LCD display JLX12864G-086

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Transistor Tester with AVR microcontroller and a little more Version 1.13k


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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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