Alongside a soldering station, a multimeter and a power supply, an oscilloscope is probably the next device in the electronics workshop that should be considered. Old analog oscilloscopes are often available used for 50 euros. For that, you usually get 2-channel devices with a CRT and 20 MHz bandwidth. There is basically nothing wrong with these used oscilloscopes, mostly from Hameg or Philips. The models Hameg HM 203 or HM 605 are recommendable here. The older models HM 305 or HM 312 are also sufficient for the hobby workshop. For Philips, I would suggest the models PM 3240 or Philips PM 3055. With the latter, however, you must ensure that the LCD displays are still in order and do not have black spots.
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However, as a layperson, you usually can’t judge whether the used oscilloscope is really functional in all areas. Often the brightness has already decreased, the calibration no longer fits or errors in the triggering, etc. spoil the fun of the bargain oscilloscope. In addition, analog oscilloscopes are large, heavy and take up a lot of space on the table. Except for the last models from the analog era (the Hameg HM 1004 or the HM 507 and HM404 come to mind), they also don’t offer convenient displays of voltage, frequency, etc., which can be regarded as standard today and is very practical. Without these displays, you have to count the vertical boxes and multiply by the selected division to estimate the voltage. For the frequency, you won’t manage without a calculator, as the reciprocal of the time base must be calculated here.
New digital oscilloscopes are available from 200 euros, which offer all these convenience functions and much more, and upwards there are almost no limits with manufacturers like Keysight, Rohde & Schwarz or Teledyne Lecroy. However, you don’t need an oscilloscope with 500 MHz bandwidth, many channels or elaborate analysis functions for the hobby workshop. For tinkering with microcontrollers like Arduinos, ESPs or Raspberry Pis, troubleshooting electronic circuits or repairing consumer electronics, 50 MHz bandwidth and 2 channels are completely sufficient.
The Fnirsi-1013D oscilloscope features and data
An interesting representative of this category and very affordable on top of that is the Fnirsi-1013D touchscreen oscilloscope. You can currently get it for about 145 euros, e.g. on Amazon . Two switchable probes are included. The Fnirsi is operated with built-in 6000 mAh batteries and thus achieves about 3-4 hours of operation. It is charged via a micro USB port, which also serves to connect to a computer to read out saved screenshots.
With its 600 grams and 182 x 124 x 50 mm dimensions, it is compact, portable but still large enough to be operated properly. With the fold-out bracket on the back, it stands at a good angle on the table.
Operation is exclusively via the 7-inch touchscreen with 800 x 480 pixel resolution, which works extremely satisfactorily. This operation is not only practical, but should also be more intuitive for oscilloscope beginners. As is usual with digital oscilloscopes, in addition to the display of the signal, values such as voltage (peak value, RMS, minimum, maximum, etc.), frequency, effective values and duty cycle are also displayed numerically. Which values are to be displayed can be selected in a menu.
Two cursors allow the measurement to be limited to a specific area of the signal. Time base and voltage range are set at the right and top edge of the screen. Likewise the settings for AC/DC coupling and the voltage divider on the probe. An auto-set function automatically sets the oscilloscope to sensible values according to the current input signal. Even a simple FFT display of the signal can be shown.
Fnirsi specifies the bandwidth as 100 MHz, which would be quite decent. The truth is more like 40 - 50 MHz. The sensitivity is 50 mV/Div. which is very little and could possibly be too little for audio applications if you are dealing with input stages of preamplifiers, etc.
As a maximum input voltage, the Fnirsi tolerates up to 400 volts (40 volts with 1x probe setting, 400 volts with 10x setting), which is sufficient for the hobby sector. Only with measurements in switching power supplies could you reach limits here, which is not recommended for amateurs anyway. Speaking of power supply: Due to the battery operation, the oscilloscope (as long as it is not connected to the PC’s USB port) is floating and you can thus measure in switching power supplies, etc. without an isolation transformer. This alone makes the Fnirsi worthwhile for just this application and saves expensive differential probes, which even in an affordable version cost as much as the Fnirsi.
Triggering can be on the rising or falling edge and the Fnirsi also has an automatic triggering that works quite reliably.
In practice
Regarding the specified bandwidth of 100 MHz, it’s a bit of a stretch. To be able to measure a signal with 50 MHz as the highest frequency component, you need an oscilloscope with 100 MHz bandwidth. If it is to be really meaningful and well resolved, one usually assumes the 1:5 rule: An oscilloscope with 100 MHz bandwidth can meaningfully and accurately display a signal with 20 MHz as the highest frequency component.
For measurements on Arduinos, etc., however, this bandwidth is completely sufficient. I applied 25 MHz in various signal forms with a Siglent function generator and the measurement result is quite satisfactory in this frequency range and can be compared with those of my RIGOL DS1054Z .
All measurements can be saved as a screenshot and/or waveform and called up via a gallery view. If you save a waveform, it can still be analyzed after the measurement as if the measurement signal were still present. 1 GB of internal memory is available for waveforms and screenshots, which can be read out via the computer. The Fnirsi is simply recognized as a removable storage device during USB operation and requires no drivers, etc.
If you enjoy Lissajous displays or want to adjust the tape head of a tape deck or a tape machine (azimuth), you can activate the X/Y display for both channels in the menu:
You have to do without extended evaluations such as mathematical functions, bus decoding, etc., which is understandable at the price asked.
Conclusion
The Fnirsi-1013D is an affordable, mobile digital oscilloscope with 2 channels and sufficient features and performance. It is very well suited for the hobby workshop, Arduino tinkerers or common repair tasks. Thanks to the built-in battery, it can work floating and can therefore be worthwhile on its own, because a differential probe costs the same.
The measured values are within the specified tolerances and the evaluation options are good. Only the low input sensitivity slightly tarnishes the picture.
Buying the Fnirsi-1013D
The Fnirsi is offered on many channels. It is cheaper directly from China, but you must of course expect import VAT and customs duties. I recommend buying via Amazon , as you don’t have to fear any nasty surprises with the total costs here, can use buyer protection and can return the device without any problems if there are issues or you don’t like it.
There are now two versions, which only differ visually. The new “white” version with the white front frame and the imprint “TABLET Oscilloscope” has the BNC sockets and the power switch recessed in the housing. This is not the case with the black version.
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