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The M181 is a small kit containing only SMD components, which allows you to measure resistors, capacitors and coils with an accuracy of ±1.0%. |
Introduction to the M181 from JYE Tech
The end result
The photo below shows the end result of this kit. A small gadget measuring 66 mm x 32 mm x 19 mm that allows you to measure four specifications of the passive components R, L and C with an accuracy of ±1.0%, which is more than sufficient for hobbyists. You power the PCB from a 5 Vdc USB power supply and connect it to the component to be measured using a simplified version of a Kelvin probe. The measurement results appear on a very bright miniature display measuring 24 mm by 12 mm. The device measures with a sine wave voltage of approximately 175 mVRMS with a frequency of 100 Hz or 1 kHz.
The M181 can be operated using three small push buttons and is otherwise fully automatic. A mini-USB to USB-A cable is included to power the circuit.
The 'housing' consists of nothing more than two transparent plastic panels, which you mount on either side of the circuit board using spacer sleeves.
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| The end result of this kit. (© JYE Tech) |
Manufacturer, suppliers and price
The kit is marketed by the well-known Chinese company JYE Tech. This company specialises in designing inexpensive kits for electronic measuring equipment for students and hobbyists. Its miniature oscilloscope kits, which cost less than € 20, such as the DSO183, are particularly well known. The M181 is another inexpensive kit. You can buy the kit for just over € 30 from all well-known Chinese mail order companies such as AliExpress and Banggood.
Look before you leap!
In the introduction to this article, we already mentioned that this kit contains only SMD components. These are not the large MELF types, the chip resistors are of the 0805 model. The capacitors supplied are not much larger! You will need to solder more than fifty of these miniature components onto the PCB, plus five ICs. This means you will need to have certain skills, such as a very good eyesight. Moreover, without the necessary tweezers, a magnifying glass and a soldering iron with a very fine soldering tip, you should not even consider assembling this circuit board.
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| The dimensions of the supplied SMD components. (© 2026 Jos Verstraten) |
Delivery of the kit
All components are packed rather carelessly in a plastic bag, which is then placed in a shipping envelope. The shipment fits through the letterbox, so you do not need to stay at home for delivery.
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The delivery of the components. (© 2026 Jos Verstraten) |
The components supplied
In the photo below, we have neatly laid out all the components supplied. Next to the PCB, you can see the display with the necessary control electronics. Underneath the display is the packaging for the various SMD components. Fortunately, extra resistors and capacitors are supplied. At the bottom right are the two measuring probes with two shielded cables, the connectors and four pieces of heat-shrink tubing. With these parts, you can manufacture the primitive Kelvin probes.
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| Overview of the components supplied. (© 2026 Jos Verstraten) |
The manual
This is not included, but comprehensive assembly instructions, the complete diagram and the user manual can be found on the manufacturer's website. We have summarised these documents into a single PDF file, which you can download from our Google Drive account:
The circuit board
This is shown in the figure below. As you can see, some components have already been mounted, including the microcontroller, which is so small that it cannot be soldered by hand. You will need to solder components on both sides of the circuit board. The resistors, capacitors and ICs go on the side shown on the left. The display, the three push buttons and the two connectors for connecting the Kelvin probes go on the side shown on the right.
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| The two sides of the PCB. (© 2026 Jos Verstraten) |
The electronics of the M181
What is measured?
The M181 applies an AC signal of approximately 0.6 V across the component at a frequency of 100 Hz or 1 kHz. The electronics extract sufficient data from the measurement results to not only calculate the value of the component, but also to display three secondary parameters:
- The value of the equivalent series resistance (ESR).
- The quality factor Q.
- The dissipation factor D.
Q and D are not that important in hobby projects. However, the ESR of electrolytic capacitors in power supplies is a specification that begs to be measured regularly!
Technical specifications of the M181
According to the manufacturer JYE Tech, the M181 has the following specifications:
- Primary measurement quantities: R, C, L
- Secondary measurement quantities: Q, D, ESR
- Equivalent circuit: serial or parallel
- Measurement signal: 0.6 Vpeak-to-peak sine wave
- Measurement frequency: 100 Hz or 1 kHz
- Measurement resolution: four digits
- Measurement accuracy: ±1 % typical
- Resistance measurement range: 0.1 Ω to 10 MΩ
- Capacitance measurement range: 1 pF to 10 mF
- Inductance measurement range: 1 μH to 20 H
- Q and D measurement range: 0 to 10,000
- Range switching: automatic
- Calibration: with open and closed measuring probes
- Measuring probes: Kelvin-type four-wire
- Supply voltage: 5 Vdc
- Supply current: 100 mA max.
- Dimensions: 66 mm x 32 mm x 19 mm
- Weight: 23 g
The operating principle
The figure below illustrates how the M181 works. This LCR tester operates according to the Thomson bridge principle, also known as the Kelvin bridge. With this bridge, powered by AC voltage, you can take measurements without the parasitic properties of the measuring cables and probe interfering with the measurement. This is because the measuring voltage and the signal to be measured are supplied and taken at exactly the same place, as close as possible to the component.
A very small sinusoidal voltage is generated in the measuring device. This is applied to the passive component to be measured via one of the four connections. This voltage is measured as close as possible to the component via a second connection. The other two connections are connected to the other terminal of the component. This point is virtually at ground, and the current flowing through the component also flows through the resistance Rref of the measuring device. M1 and M2 are not ordinary voltmeters, but circuits that measure not only the magnitude but also the phase of the applied voltage. The processor in the meter can derive a lot of properties of the measured component from these two measurements, such as value, impedance X, ESR, phase shift φ and quality factor Q.
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| The operating principle of the M181. (© 2026 Jos Verstraten) |
The Kelvin measuring probes
If you look at the first photo in this article, it appears as if the M181 comes with two single measuring probes. However, this is not the case. The probes are connected to the M181 by means of two shielded cables containing two wires. These two wires are only soldered together at the tips of the measuring probes. On the PCB, they are connected to the electronics by means of three-pin connectors. A very inexpensive and simple design for Kelvin probes!
The complete diagram of the M181
The figure below shows the complete diagram of this LCR meter provided by the manufacturer. Click on the figure with the left mouse button to enlarge this diagram on your screen.
The two measuring probes are connected to connectors J1 and J2. The signals are sent to a 74HC4053, a triple two-channel analogue multiplexer/demultiplexer. This is followed by a differential amplifier around U2A, U2C and U2D. From the output of this amplifier, the measurement signals are sent to the microcontroller.
The sine wave is digitally generated via a 300 Ω / 150 Ω ladder network from outputs DA0 to DA7. U4C and U4D form a low-pass filter, which converts the staircase sine wave approximation of the ladder network into a smooth sine wave. This goes via R22 to connector J1 and from there to the component to be measured. The bottom of the diagram derives the necessary additional supply voltages of -4.5 Vdc and +3.3 Vdc from the available +5 Vdc power supply.
The CH340N, at the bottom left of the diagram, is a USB-to-serial (UART) converter. This provides communication between a PC and the circuit, for example for upgrading the software.
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| The complete circuit diagram of the M181. (© JYE Tech) |
Assembling the M181 LCR-meter
Mounting the ICs, resistors and capacitors
The drawing below shows the component layout on the PCB. The reference designators are not shown on the PCB, so this image is the only guide to the correct location of all SMD components that you need to solder onto the PCB. The components in yellow are already soldered onto the PCB. Why some resistors and capacitors are already present on the PCB and you have to solder the others yourself is a mystery. The many test points on which you can measure certain voltages are shown in red. This is described in the manual. Finally, the various jumpers are shown in green, with JP3 being particularly important. Read on for more information.
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| The component layout on the PCB. (© JYETech) |
The manual recommends first placing the ICs, then the resistors and finally the capacitors on the circuit board. The table below provides a complete overview of all SMDs that you need to solder.
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| All the SMDs that you need to solder. (© JYE Tech, edit 2026 Jos Verstraten) |
Once you have arranged all those components neatly on the circuit board, the really difficult work is done. You can see what we have put together in the photo below. As you can see, our soldering work is not exactly a thing of beauty, but we can claim extenuating circumstances due to our age (78), our poor eyesight and artritis in our finger joints. If we can do it, then you certainly can too!
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| The SMD side of the circuit board. (© 2026 Jos Verstraten) |
Assembling the other side of the circuit board
Here you only need to solder six components:
- The three push buttons
- The two input connectors
- The display via a four-pin header
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| The other side of the PCB. (© 2026 Jos Verstraten) |
The construction of the Kelvin measuring leads
This is described in detail and well documented in the manual. The only problem we encountered was that the heat-shrink tubing included in our kit did not fit through the connectors' handles. We therefore had to drill the holes in those handles slightly larger. When soldering the cables to the plugs, take care to ensure that the two wires of the cable do not short-circuit each other in the plug or come into contact with the shielding!
Working with the M181 LCR-meter
Checking your work
Connect the circuit board to a 5 Vdc power supply using the supplied USB cable. Then measure all voltages as indicated in the manual. If these are OK, bridge the two parts of jumper JP3 with a small amount of solder. We had overlooked that one sentence in the manual, with the result that we searched in vain for a soldering error that wasn't there. The display should now become active. After two introductory screens, the display will remain idle with the information shown below. The top line shows the selection of Ser/Par and 100 Hz/1 kHz.
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| The screen when you don't measure anything. (© JYE Tech) |
Adjusting the device
Connect both probes to the circuit board and ensure that the pins do not touch each other. Now press and hold the 'HOLD' button for more than two seconds. The text 'Open zeroing' will appear on the top line of the display and the microcontroller will now perform a number of tests to compensate for the parasitic properties of your probes.
Briefly connect the two pins of the probes and press the 'S/P' button for longer than two seconds. Please note that this step is incorrectly described in the manual. The text 'Closed zeroing' will appear on the top line of the display. The resistance of your Kelvin probes will now be measured and compensated.
Your M181 is now ready for use.
The function of the push buttons
- Push button 'HOLD':
After briefly pressing this button, the reading is frozen and you can read all the data from the display at your ease. - Push button 'P/S':
Selects between a parallel or serial equivalent diagram. - Push button 'RCL':
Selects the type of component you want to measure: resistor, capacitor or coil. If you press and hold for more than two seconds, you can switch between 100 Hz and 1 kHz.
Testing the M181 LCR meter
Test conditions
We test at a frequency of 100 Hz and with a serial equivalent circuit. We power the device from a 5 Vdc power pack.
The measurement voltage
We checked the measurement voltage with our oscilloscope. As shown in the oscillogram below, this signal looks perfect. It is symmetrical around zero; there is no option to superimpose the sine wave on a small DC voltage when measuring electrolytic capacitors.
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| The measurement voltage of the M181. (© 2026 Jos Verstraten) |
Measuring resistances
For this test, we have a set of reference resistors with a tolerance of ±0.01%. In addition, we measure a few less accurate resistors in the very low and very high ranges. We use our old, trusted Fluke 8842A as a reference meter. The results are summarised in a clear table and can be described as excellent.
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| The accuracy when measuring resistors. (© 2026 Jos Verstraten) |
Measuring non-electrolytic capacitors
Thanks to a set of accurate capacitors with a tolerance of ±1% and a pair of reference capacitors with a tolerance of ±0.05%, we can accurately map the performance of the M181 when measuring such components. We use the ET4401 from EastTester as a reference meter, with an accuracy of ±0.2 % for non-electrolytic capacitors. These results are also impressive. What is striking is that the M181 also measures small capacitors accurately. The 100 pF capacitor is measured completely within its tolerance of ±1%!
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| Measuring non-electrolytic capacitors. (© 2026 Jos Verstraten) |
Measuring electrolytic capacitors
We have summarised the measurement data for five electrolytic capacitors from our stock. What is striking is the large difference between the measurement results of the M181 and the ET4401 when measuring the 10 mF electrolytic capacitor. Which one is correct?
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| Measuring electrolytic capacitors. (© 2026 Jos Verstraten) |
Measuring the ESR
The ESR (Equivalent Serial Resistance) is a virtual resistance that is in series with the capacitance C of the electrolytic capacitor. This ESR is mainly important for electrolytic capacitors in the smoothing of power supply circuits. Two large currents flow alternately through such an electrolytic capacitor: the charging current from the rectifier to the electrolytic capacitor, and the discharging current from the electrolytic capacitor to the connected electronic circuit. It is clear that the ESR, which causes voltage drop and heating, must be as low as possible.
The table below shows that both meters display quite different measurement results. Once again, we are faced with the for us unanswerable question: 'who is right?'.
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| Measuring the ESR of electrolytic capacitors. (© 2026 Jos Verstraten) |
Measuring coils
Unfortunately, we do not have any accurate reference coils in-house. We are therefore unable to perform an accuracy test, but can only provide a comparison between the measurements taken with the M181 and our ET4401 from EastTester. These results are summarised in the table below. When measuring an induction of 1 μH, the M181 does not give reliable results; the numbers jump from high to low and vice versa. For the larger values, both meters are fairly consistent with each other.
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| Measuring coils. (© 2026 Jos Verstraten) |
M181 LCR-meter kit
