FNIRSI-1C15 Mini Oscilloscope

Back in March, I was asked to write a review of the 1C15 mini oscilloscope. I can't say I was eager to do it, but I was curious to take it apart and explore it. There were two reasons: it's a popular model, and people had also asked me several times about a simple oscilloscope for basic work on power supplies.
Well, I finally got one and did a little testing.


I'll say right away: don't think of this as a professional device. It's just a small hobbyist oscilloscope, or perhaps more of an advanced oscilloscope probe. I've already reviewed both a very basic DIY kit and an interesting model from Taobao, and I also occasionally use the well-known DS203. But I'm getting a little sidetracked.

No complaints about the packaging. Not only was the box a decent size, everything inside was carefully wrapped in film, and the oscilloscope itself was sealed in a bag to protect it from moisture.


Everything is packed in a neat, sturdy zippered case. In my opinion, it's better than the DS203's packaging, which came with only a soft pouch and a cardboard box.


At first glance, the package seemed extensive, but in reality it's much more modest:
1. 1C15 oscilloscope
2. Probe
3. USB cable
4. Manual
5. Case


The manual is in English and Chinese, but it's generally easy to understand.
It also comes with a USB-to-microUSB cable for charging and firmware updates, and here's where there's a problem. The microUSB plug is noticeably longer than standard, which could cause trouble down the road, especially if you lose it, since I haven't seen cables with plugs this long for sale.


The manual also lists the specifications, but I'll give them separately.


The probe is a basic one, and the package is bare-bones: they didn't even include a spring for making a connection without the ground lead and its alligator clip. On the side opposite the label, there's a hole for adjustment.


The description didn't say anything about the cable for this oscilloscope model, but for its "brother" the manufacturer warned that the 100 MHz bandwidth is available with the attenuator set to x10, while in x1 mode it's only 5 MHz.


My first impression when I picked it up was that it felt a bit basic, although the bright case gives it a lively look.


After placing the order, I thought it might have been more interesting to take a look at another model, the 5012H. Its technical specifications are similar, but it seems to offer more features for about the same price. Still, I got what I got.


Here's a comparison with the DS203. I'd say the model under review loses out noticeably in terms of appearance. The DS203 looks solid, at least partly because it has a metal case and is much smaller, despite offering more features. The 1C15, on the other hand, looks more like a pretty decent project from a children's technical club. Unfortunately, that's how it is.


A closer look: you can immediately see that inexpensive plastic was used. The labels are only on the buttons, but at least the buttons are divided into two color groups for easier use.


The charging indicator and power switch are on the bottom edge. It's awkward to use the switch while the oscilloscope is in its case; you have to poke your finger in. The hole for the LED looks like it was punched out with an axe—it's very rough.
The probe socket and microUSB port are on the top edge.
The protective case has feet to keep it from sliding around.

The last photo shows what I mentioned earlier: the connector is recessed deep into the case. In effect, the oscilloscope comes with something like a proprietary cable, meaning one you can't buy "on every street corner," which could cause problems down the road.


The case is comfortable and soft, and I'd even praise it if not for the tiny opening for the power switch, which makes it awkward to use.


All the controls are on a keypad with 16 buttons plus a joystick that works like a slider. I have no complaints about the buttons, but the joystick isn't very convenient. Personally, I think they should have used four more buttons instead, like on the 5012H.
In any case, the controls here are simpler than on the DS203. It has fewer controls but more functions, which makes it harder to operate.


The controls are intuitive. In simple terms, the buttons do the following:
OK - Confirms an action when needed.
50% - Sets the zero reference for both measurement results and the trigger position or level.
Menu - Settings menu
Stop - Holds the readings, like the Hold function on a multimeter
Auto - Automatically sets the measurement parameters, sweep time, voltage, and trigger
REF - Captures a waveform snapshot, then overlays new waveforms on it
X1X10 - Selects the display mode. Set it to match the switch on the probe so the displayed voltage is correct.
S/nS - Increases/decreases the sweep time
V/mV - Increases/decreases the voltage measurement range, V/div
ACDC - AC/DC coupling; the second option is used to measure DC voltage
Meas - Displays numerical measurement results such as voltage, frequency, etc.
Single - Single trigger mode
Save - Saves a screenshot of the measurement results
Sel - Sets the trigger threshold.

The joystick moves the waveform up/down and left/right. It is also used to navigate menus and adjust settings.


When switched on, the device displays the company name, Rubyster, then the oscilloscope enters normal operating mode.
The main screen shows the working area. At the top left are the operating mode (Auto, Stop, or Wait), the horizontal position scale, and the battery charge indicator. The bottom shows numerical measurements, frequency, peak-to-peak signal amplitude, and duty cycle.
At the very bottom are the selected operating settings: vertical scale (V/div or mV/div), AC/DC coupling, signal attenuation, and sweep time.

The screen resolution is not very high (320x240), but since it doesn't display much information, everything remains easy to read.


The menu has six sections:
1. Default operating mode - AC/DC and x1/x10
2. Options for displaying numerical information on screen
3. Persist - phosphor emulation: off, 1-second refresh, or no refresh. Roll - I couldn't figure out what this does.
4. Default trigger mode
5. Oscilloscope calibration
6. Language selection and firmware version.


1. When Auto mode is enabled, the oscilloscope clicks its relays for a few seconds, then gradually finds a suitable operating mode and settles down.
2, 3. If you try to exceed the set limits for sweep time or voltage range, the display shows “Limited.” The voltage range is 20 mV–10 V, and the sweep time range is 5 ns–10 s.
4. Pressing the 50% button opens a menu where you can choose what to zero. By default, it offers to zero everything, but you can select just the input zero or the trigger settings.
5. Meas displays all the numerical measurement results, but it's not very convenient to use this way. It's better to customize the bottom section to suit your needs.
6. Pressing Stop “freezes” the display.
7, 8, 9. The Save button lets you save a waveform screenshot at any time. Long-pressing it opens the saved screenshots, where you can view or delete them. Numerical data isn't displayed, but worse, you can't save the screenshot, and it doesn't show either the capture date or even a number, which almost defeats the purpose of this feature.


Before running the tests, I decided to update the firmware just in case. The latest version available at the time was from March 2020.
To download it, follow the link, then save the archive.


The archive contains a single firmware file.


Updating the firmware is very simple: turn off the power, hold down the SEL button, and switch on the oscilloscope. Release the button when the splash screen appears.
The screen will then display instructions for updating.
Connect the USB cable, and a new 750 kB drive will appear in "My Computer". Copy the firmware file to it. When the copy is complete, press OK on the oscilloscope and wait for the firmware to update. Once it's done, turn the power off and back on.
The first thing I noticed was that the splash screen and version number had changed. Otherwise, nothing seemed different—not even the settings I'd configured manually; they were still in the same state.


I couldn't resist taking it apart, especially since the case is held together with just four screws—there aren't even any clips.


Inside is an unbranded battery glued to the bottom half of the case.


The circuit board looks quite neat, although the overall impression is that it's basic and somehow rather empty.


After removing four more screws, you can take out the board. It looked to me as though the screws hadn't been screwed in during assembly, but simply pressed into the plastic.


The screen looks very similar to the one used in the basic oscilloscope DSO138—at least, the appearance, dimensions, and resolution are the same.


1. Input section. You can see the electromechanical relay that switches the measurement ranges. It also looks like there's a solid-state relay for AC/DC mode above it.
2. Probe input jack
3. Of all the larger chips, only the memory chip's markings are legible; the markings on the others have been carefully removed.
4. Near the power switch are a logic IC, memory presumably used to store the firmware, and a charging chip—the basic TP4056.
5, 6. Display markings; I found a couple more components under the ribbon cable.


The input attenuator circuitry is extremely simplified. A single relay switches the ranges, splitting them into two subranges: 20–200 mV and 500 mV–10 V. The rest is probably handled by changing the gain of the input amplifier. For example, the previously shown simple oscilloscope used five relays for this.


The keypad is very basic, but feels great to use. At least, I liked how it worked.


I didn't take the joystick apart because it's very awkward to disassemble: you have to release several clips at once. But as I mentioned above, I think four regular buttons would have been more convenient.
There are quite a lot of flux residues on the board, left over from soldering the separate keypad board in place.


The device fully disassembled.


The specifications say it has a 3 Ah battery that takes 4 hours to charge, with a runtime of 10 hours.


I used the oscilloscope itself to fully discharge the battery, then connected the charger. The red LED came on, and the charging current was about 700 mA. After a couple of hours, it gradually dropped to 600–650 mA.
After about 5 hours, the battery was fully charged and the LED turned blue. The charge put back into the battery was about 2450 mAh.


Now let's measure the current draw and work out how long it can run on that capacity.
1, 2. It turns out the current draw depends on the selected input voltage range, so it's higher when the relay is energized.
3, 4. It also turns out the oscilloscope itself has no protection against operating at low voltage; everything is handled by the battery protection board. Also, at 3.1 V and below, the zero level drifts—the built-in reference voltage source probably can't operate properly anymore. The lowest voltage at which the oscilloscope still tries to work is 2.4 V. There's no image, but it still doesn't shut down.

So, with a capacity of 2.45 Ah, the oscilloscope will run for about 6.5–7.5 hours, depending on the operating mode. In other words, actual runtime is one and a half times shorter than claimed.


The built-in memory is large enough to let you examine the waveform over a fairly wide range while the oscilloscope is paused.
For example, I stopped acquisition at a 5 µs timebase, then comfortably changed it to 50 ns. In this mode, the full range was 5 ns–50 µs; at 100 µs, the waveform occupied only half the screen.


Additional features.
1, 2, 3. Waveform overlay mode: press REF to capture a waveform snapshot. You can then view two traces at once: the static snapshot and the live waveform. You can compare them overlaid, offset them, or even change the timebase settings.
4, 5. Phosphor emulation mode. The first option keeps only the last second in memory; the second does not erase the trace, effectively acting as an accumulation mode. I wouldn’t call this a particularly important feature, but it could certainly come in handy.
6. Slow timebase mode. The oscilloscope supports a timebase of 10 s/div, so you can fit 120 seconds of measurements across the screen. The resolution won’t be great, of course, but it works quite well as a basic analyzer for slowly changing signals.


For my first test, I ran the oscilloscope in DC mode—that is, with the input open—to check its voltage measurement accuracy.
1. I immediately ran into a quirk: setting the zero level is easy enough, but you can’t smoothly shift it by several divisions or set a specific offset. The adjustment is very coarse. I got as close as I could, offsetting the trace down by 3 divisions, and set the scale to 1 V/div.
2–9. Voltage measurements at 1, 4, 6, 10, 20, 40, 50, and 60 V. In almost every case, the reading was slightly below the actual value—not a critical error, but still. You can view the measured voltage either from the waveform or as a numeric value in the Mean field.

I wasn’t expecting miracles in terms of measurement accuracy; an oscilloscope is a very crude measuring instrument. But in this case, what stood out was the awkward vertical adjustment.


For the next tests, I really needed a signal generator, preferably a high-frequency one. Unfortunately, due to an unfortunate turn of events, the one I was planning to borrow had been fried, so I had to improvise.
I used the DS203 oscilloscope as a signal generator. It can output square waves up to 8 MHz and more complex signals up to 20 kHz.
My Rigol DS1054 served as the reference.

First, 20 kHz sine and triangle waves, then square waves at 2, 4, 6, and 8 MHz.


Now the same tests with the unit under review.


And now the DS203. I can already say that it clearly falls short of the unit under review.


For higher-frequency tests, I dug up a few crystal oscillators at home. They’re not exactly ideal reference sources, of course, but comparing them with my main oscilloscope is perfectly feasible.


Frequencies of 16, 24, 30, and 34 MHz. I was surprised to see a fairly good square wave from the 34 MHz oscillator.


At these frequencies, the unit under review is already noticeably behind. I didn’t test the DS203 at all; these frequencies are far too high for it.


But it turned out things might not be as bad as they first seemed. The cheap cable included in the box has a pretty big effect. The original Rigol cable is on the left, and the cable supplied with the 1C15 is on the right. Frequencies: 16 and 34 MHz.
I considered using two channels for the comparison, but that setup has a noticeable effect—the generator simply can’t drive the load. Also, because of its design, the Rigol cable can’t be connected to the unit under review.


But I think a test under conditions closer to real use is more interesting. In this case, that means testing a power supply. I used an electronic load and a 24 V power supply.


I measured the ripple amplitude with no load, at currents of 2 and 6 A, and, as an additional test, at 6 A with a different timebase setting.


I wouldn’t say the unit under review performs much worse. I did have to set the probe attenuation to x1, though, because at x10 the minimum scale is 200 mV/div, while this test requires at least 50 mV.


The DS203 was also set to x1 for the reason mentioned above. I’d say the result is perfectly acceptable too.


So, what can I say in conclusion? The oscilloscope pleasantly surprised me. In terms of features, it’s clearly outclassed by the DS203, which has four channels (2 analog + 2 digital), a built-in signal generator, screenshot capture, and so on. But in terms of electrical performance, the 1C15 is noticeably better. That’s down to its much higher sampling rate: 500 MSa/s claimed, compared with 72 MSa/s for the DS203. And the DS203’s 72 MSa/s is shared between two channels, so that’s 36 + 36.
Of course, all these megasamples are a bit like “spherical horses,” but even so, 36 versus 500 is no contest.

Perhaps the biggest thing I didn't like about the 1C15 was the lack of a way to save screenshots—or, more precisely, transfer them to another device. The built-in viewer is useful too, of course, but it's really just a workaround.

All in all, I think it's a pretty good device, well suited for testing power supplies and the like. You could certainly replace it with something more substantial, but this one has full galvanic isolation on its side, as well as—strange as it may sound—a metal case. The DS203 is convenient too, but less safe, and it's also outdated, though considering how old it is...

That's all for today. I hope you found this useful, and as always, I'll be glad to hear your questions and comments.