Fnirsi LCR-ST1 Smart LCR SMD Tweezers
- by Harry Baggen
- Reading time: 7 min
Recently, both Zoyi and Fnirsi have released affordable smart tweezers that also measure inductance, and for just a few dozen euros. In this review, I explore what the Fnirsi LCR-ST1 can do for such a low price and evaluate its practical usefulness.
Identifying and measuring passive SMD components is often challenging. These parts are usually tiny, and you can’t always tell by their shape whether they’re a resistor, capacitor, or inductor. To make measuring these SMDs easier, some manufacturers introduced “smart tweezers” years ago—a miniature LCR meter with tweezer-shaped probes that can clamp onto an SMD component to measure it. The original devices were (and still are) quite expensive, and soon after, affordable Chinese versions with similar designs emerged. The main drawback, however, was that these cheaper versions (with few exceptions) could only measure resistance and capacitance, not inductance.
The Fnirsi LCR-ST1: a Lot of Meter for Little Money
Opening the packaging of the Fnirsi LCR-ST1, it’s hard to believe what you get for under 40 euros. In a neatly lined case, you’ll find the measuring tweezers themselves, two extra measuring tips with a curved front, a USB-C cable, and a magnetic plate for attaching the tweezers. There’s also a small manual in Chinese and English, which, though brief, covers all the essential information you need to use the instrument.
The housing of the measuring tweezers is about 6 x 2.8 x 1.9 cm and features a 1.14-inch color display. Two measuring probes, each roughly 9 cm long, extend from the narrow end of the case. Screws secure the metal tips at the ends, you can tighten or loosen them without tools, making it easy to switch to the other tips that the set includes.
The controls are minimal. Next to the display, there is an on/off button and a memory button. On the side, there’s a three-way toggle switch that moves left and right; you can also press it. I’ll explain its functions in detail later. The USB-C port on the narrow side allows for charging the LCR-ST1’s internal battery and connecting it to a PC.
The Possibilities of the Fnirsi LCR-ST1
When turned on, the LCR-ST1 starts in auto mode, automatically identifying whether the component under test is a resistor, capacitor, or inductor. The primary measurement (up to four digits) is visible prominently in the center, with the series resistance (R) and dissipation factor (D) below in smaller text. The measuring voltage (at the top) can be either 0.6 V (default) or 0.3 V by using the three-way switch. The lower voltage setting is useful for in-circuit measurements, as it avoids detecting diode transitions. The device also displays the measuring frequency. You can adjust it with the same switch to 1 kHz (default), 100 Hz, or 10 kHz. I didn’t expect such versatility from such an affordable measuring probe.
Keep Track of Measurements
You can freeze measurements with the memory button; the device’s also stores them in its memory as a CSV file. You can access these measurements later on a PC via the USB connection. The same USB connection allows for easy firmware upgrades. Pressing and holding the memory button opens a setup menu where you can adjust settings such as display brightness, buzzer volume, and auto-off timing. The display is quite bright, so I reduced the brightness slightly for regular use.
Auto and Manual Mode
Besides auto mode, you can manually select resistance, capacitance, or inductance measurement using the three-way switch. In a fourth position, the LCR-ST1 can measure diodes. Due to its low measuring voltage, it only measures standard diodes, not LEDs. A unique feature of diode measurements is that the display shows the diode’s polarity, regardless of the diode's orientation, as the probe automatically detects it using alternating voltage.
The Fnirsi LCR-ST1 in Practice
The LCR-ST1 is lightweight at just 40 grams and fits comfortably in hand. It powers on and is ready to use in about a second. The display is crisp, with clear, easy-to-read values from any angle. The controls are intuitive, and operation becomes straightforward after a few tries, even without the manual. The metal measuring tips are quite sharp, though some users might prefer them even sharper for measuring components soldered onto a PCB—an easy fix with a file.
In-Circuit Testing
I tested various components individually and some directly on a PCB; it was quicker and more efficient than using the SMD measuring tweezers on my larger LCR meter. When measuring components on a PCB, having the circuit diagram handy is helpful to understand which parts are connected. In auto mode, the meter reliably identified nearly everything. Wired components also measure well on this device. The grooves on the inside of the tips securely hold small component leads, like those of capacitors, for easy measurements without them slipping.
Built-In Calibration Feature
The measuring tweezers have a built-in calibration feature to compensate for the resistance between the tips. Calibration is done by pinching the tips together and briefly pressing the on/off button, though I didn’t notice much effect. When the tips were closed, the meter showed a value of a few milliohms, which barely changed—a remarkably low resistance of 2 to 5 milliohms for such a basic device. There appears to be an additional calibration menu accessible by pressing the three-way switch left while turning on the device, though the exact procedure remains undocumented.
Accuracy of the Fnirsi LCR-ST1
To test the accuracy, I measured various resistors, capacitors, and inductors, comparing results with my primary LCR meter (accurate to 0.5%). I was genuinely surprised by the results: most measurements were within 1% of the larger meter's values. Only with larger inductors and capacitors, like a 4700 µF electrolytic capacitor, did accuracy decrease, but stayed within Fnirsi's specs at around 5%. The series resistance and dissipation factor also displayed impressive accuracy, though a minor drawback is the tweezers showing a dissipation (D) value for inductors rather than a quality (Q) factor—likely meant as 1/Q. This is something they could improve in future firmware, but overall, I’m very pleased with the unexpectedly high accuracy.
Conclusion
The Fnirsi LCR-ST1 is an extremely convenient tool, essential for anyone working with SMDs. It quickly identifies components with impressive accuracy and allows for selection among three measuring frequencies and two voltages, making it suitable for in-circuit measurements as well. Wired components are also easy to measure. Although I have a “large” LCR meter, this device is far easier for quick measurements or checks—especially given its incredibly low price. It’s a permanent fixture in my hobby lab!