DIY Electronics Tester Kit M168

I saw an interesting kit at and decided to try it: DIY Meter Tester Kit For Capacitance ESR Inductance Resistor NPN PNP Mosfet M168 . The reasons for interests are good specifications, based on open source hardware design and price is reasonable ($12.22 / 9.37 Euro).

DIY Meter Tester Kit For Capacitance ESR Inductance Resistor NPN PNP Mosfet M168 is an electronics component measurement device. It can detect component types and measure them. The meter has automatic detection PNP and NPN type bipolar transistors , N, P -channel MOSFET, JFET FET , diodes , two diodes, thyristors , resistors , capacitors , inductors. You can connect the measurement wires to components as you want, the automatic detection pin definitions will tell which wire is which pin.

The meter features single key measurement operation: Just press key and meter does measurement automatically (determine component type and measure it’s values). Each test time is about two seconds , only large capacitance and inductance measurements will take a long time. The device has auto power off with delay.

The device can be powered with 6FF22 9V Battery, or DC 5.5V ~ 12V via DC socket. The kit has 25 mA operating current and 20 nA current in shutdown, so suitable for battery operation (without separate power switch).


Measurement Ranges:

Resistor: 0.5Ω ~ 50MΩ (resolution is 0.1Ohm)
Capacitor: 30pF ~ 100mF (resolution up to 1PF)
Inductance: 0.01MH ~ 10H

Potentiometer: Support two measuring resistors connect at the same time -> can measure potentiometer

ESR measurement: Can detect more than 2UF capacitor equivalent series resistance (ESR), with a resolution of 0.01Ohm.

Bipolar transistor: amplification factor (B) and conduction voltage emitter junction (Uf).

MOSFET: threshold voltage and gate capacitance measurement

Thyristor and TRIAC: meter shows only the component pin-out

Diode: diode direction, voltage drop and capacitance

Zener-diode: If reverse break down Voltage is below 4.5V, these are shown as two diodes with different voltage drops

This device is sold as DIY kit that you must solder yourself. The kit comes in a small plastic bag that included all the components and circuit board.


The parts and board are excellent quality, no missing or wrong parts.


Beginners beware – there are no instructions or documentation with this “kit”, it is a PC board and a bag of parts. That’s it. But, that’s okay because when you install the parts per the component outline/value printed on the top of the PC board.


When you put all components in right places add the solder – you’ll end up with a working instrument.


Only problem I had building: There was no clear indication the way the button should installed to circuit board. I first accidentally installed in wring way, and the circuit worked a little bit strangely (but almost worked). When I turned around it (needed de-soldering and re-soldering), everything stated works well as designed.


Here is my circuit (with my own measurement leads added to kit) measuring BS170 FET:




This kit is an accurate implementation of the open source project described in all detail at and a newer version of it at Since the PC board in this kit implements the open source project schematic with 100% accuracy, the board also uses the open source AVR code. This allows you to extend the design, change its behavior or just use it as is, the choice is yours.

This version uses the ATMEGA328P-PU  (same 28 pin DIP package that the Arduino UNO uses). The unit does provide the same 2.1/5.5 MM power jack as used on Arduino’s if you want to power it with a 9vdc wallwart.

There are few negative things on the design:

1) The press to test switch is lacking a large surface to press.You might want to add a small cap to it or replace the original button with your own more user friendly button.

2) The choice of LCD (white on blue) requires the use of the LED backlight always. This backlight uses considerable battery power. The display is standard 1602 device so it should be possible to change if you want to experiment (cost few dollars).

3) The placement of the 3 point terminal strip in front of the SMD pad areas is not good:  Having the terminal in front of the pads makes it almost impossible to easily test surface mount parts by pressing them on the board. If you always use measurement wires this is not a problem.

4) The ATMEGA328P processor: while it was in a good static shielding bag, there was no lead protection, it was just tossed in with the other parts which resulting in some bent pins.

5) ESR measurement and the results of inductance measurement are not very accurate.

There are some negative things, but overall I was very satisfied with DIY Meter Tester Kit For Capacitance ESR Inductance Resistor NPN PNP Mosfet M168 kit. This useful instrument will sit on my electronics lab for a long time.


  1. Niclas Ek says:
    Did you make any reference measurements on ESR and inductance? It would be interesting to know the accuracy of this meter.
  2. Tomi Engdahl says:
    The claim that “ESR measurement and the results of inductance measurement are not very accurate” is based on fact that the measurement results vary quite much (up to several percent at some cases) between different measurements made by just pressing the button (not changed anything). This variation applied to certain inductance and ESR measurements. On some other components with different values those seemed to have better accuracy (less changes in values).

    Also the original design documentation said “ESR measurement and the results of inductance measurement are not very accurate”

    I might do some more measurements against some other instruments…

    • Tomi Engdahl says:
      I did some testing comparing my RCL meter (Lutron LCR-9063) to M168 kit. The results with several half watt resistor size coils were quite accurate (few percent or less error typically). When I measured transformer coils or large chokes with ferrite or powder core, the results varied often 10-30 percent (few cases even more). Those same coils can give slightly different results in every measurement with m168 and stable reading on other meter.
  3. Tomi Engdahl says:
    Inductance measurement method use in M168 according to pages 51-52

    The measurement of inductance values will be done as separate part with all found resistors with
    less than 2100 . The methode of measurement is based on the growing of current by formula
    after switching on the current. The time constant is proportional
    to the inductance L, but reverse proportional to the resistor R. The current can only measured
    indirectly with the potential drop of a resistor.

    The measurements are always done in both current directions. The
    program will select the higher result of measurement in the same current direction, but the lower
    result of the diFFerent current direction as the displayed result.

    The Inductors above 1H are relays or primary sides of power transformers, for which measurements
    are difficult because the iron core has residual remanence.

  4. Tomi Engdahl says:
    ESR measurement techniques used according to pages 40-43:

    If the measured capacitor has a capacity of more than about 2F, the tester will try to measure the
    series resistance too.

    Strictly speaking the ESR of a capacitor depends on the operating frequency and temperature.
    Usually the value measured with sine wave-form signal of 100 kHz is denoted in the data sheets. This
    measurement can not be done with the ATmega without external equipment.

    the voltage of both connections will be measured during
    oading in one direction with the ADC internal reference voltage (1.1 V). After the measurement
    the load current will be switched off and the voltage of the capacitor is measured again without the

    The difference of capacitor voltages with and without current is proportional to the internal
    resistance of the capacitor. The expected voltage of this difference is so low, that one measurement
    can not result to a feasible result.

    Anyway the results seems to be practical

  5. Tomi Engdahl says:
    I did some testing on the ESR measurements against my homebuilt ESR meter circuit I built some years ago. It seems that the ESR measurement on M168 give useable results for identifying if electrolytic capacitor is good or that. On some capacitors the results were pretty similar on both instruments, and on some other there was some variation. But in each tested case I got results that were useful for determining if capacitor was OK or not. The ESR measurements are never so that you are interested in accurate milli-ohms reading, you just need reading from which you can determine if the tested capacitor is OK (ESR resistance in good and expected range) or it is bad (ESR considerably higher than you would expect from good one).

    Here is link to my earlier posting on ESR meters:

  6. Tomi Engdahl says:
    This looks like a ready made boxed version of M168 kit:

    MK-168 Transistor Tester Diode Triode Capacitance ESR resistance Meter

  7. Sylvain Lazare says:
    Hi Tomi Thanks fort your nice presentation. I a wondering if eventually the program is lost or damaged somehow, how tout reload it into the AT328. Is it available somewhere? Sylvain

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