New oscilloscope from Fnirsi DPOS350P

[DaneLaw]

I never noticed the lines before.  They are only visible in certain lighting.  This photo was adjusted to make them more prominent.

Could look like some LCD light guiding plates, which are used on some of the cheaper LCD panels.
That elongated form factor doesn't look like it's part of the digitizer.
If you have a microscope.. You can usually zoom down and see which part of the LCD layering it is.

[Grandchuck]

Here is a comparison of a Siglent SDS2204X and the Fnirsi using its generator .  Good agreement.

Plus model ?
Try 10bit mode for higher accuracy.

Lazy typing ... my Siglent is the HD model.

[Grandchuck]

Here is a comparison of a Siglent SDS2204X and the Fnirsi using its generator .  Good agreement.

It's pretty good. I bet the DC offset of your DPOS350P generator is good too, because (I think so now) offsets are calibrated using oscilloscope ADC. It seems reference voltage of ADC is not enough accurate in common case. But in yours it is close to nominal. Can you measure DC offset of the DPOS350P generator by DMM?

With the 1V, 1kHz square wave, it measures +3.1 mV.

[BillyO]

With the 1V, 1kHz square wave, it measures +3.1 mV.

I think he means put the generator into DC mode (it's one of the waveforms), set the "Offset" to 2V, then measure with either your SDS2204 or a DMM (or both).

Wen in this mode you can set the frequency to 0 and the amplitude to 0 too.

[Grandchuck]

DC mode:

1/ Offset set to 2.5, DMM reads 2.507
2/ Offset set to 2.0, DMM reads 2.007
3/ Offset set to 1.0, DMM reads 1.007
4/ Offset set to 0.5, DMM reads 0.507
5/ Offset set to 0.0, DMM reads 6.888 mV
6/ Offset set to -0.5, DMM reads -494 mV
7/ Offset set to -1.0, DMM reads -994 mV

[BillyO]

Nice!

[Martin Brubaker]

Well. I was wrong that the signal generator offset is calibrated during autocalibration. No, it is not calibrated. Only channel offsets are calibrated. I "fixed" my oscilloscope.
Thanks to @pcprogrammer. His post #185 clarified a lot, including the ADC type (MTX2088). After checking the datasheet, I tracked down where the reference voltage for the ADC is formed. What a quest, I tell you. Due to the aggregation of essentially 8 ADCs in 3 possible configurations, the reference voltage to the ADCs comes through analog switches from two sources. But I found it anyway. I reduced it from 1.237 V to the required 1.18 V by fiddling with the voltage divider. After that, the oscilloscope began to normally show signal amplitudes without an error of -7%. The offsets floated away a lot. After autocalibration, the offsets returned to normal. This did not affect the signal generator offset in any way, apparently it is calibrated at the factory. However, the accuracy of the signal generator offset did not bother me, unlike the oscilloscope.
It is still necessary to thoroughly investigate whether my modification has damaged any functions, but at first glance everything is fine. This problem could easily be solved in the firmware by adding a manual calibration mode using a reference signal, but here you can only rely on Fnirsi.

But my joy was overshadowed by the fact that I found another bug, much worse than the predictable systematic error, there is no time for perfectionism here... When trying to measure a signal with a frequency of 85 kHz and an amplitude of 40 Vpp, I encountered the fact that the touchscreen began to glitch indecently, and sometimes the interface even completely froze (measurements continued). Then I went further and tried to measure the voltage of 160 V and a frequency of 46 kHz, and then just dancing began. Multiple false touches. And it is enough to connect only the ground clamp to start the problems. Here you have battery power, here you have galvanic isolation from the AC-line. This is a failure. I have come to the conclusion: capacitive touch control and oscilloscopes should live in different worlds.

[BillyO]

Good job!

Would you mind sharing a picture of the location of the voltage divider for those that might want to duplicate your efforts?

As for the touch screen, does it work better if you ground the unit?  The touch screens on my Siglent scopes seem to work just fine.

[Atlan]

Was that 7% deviation on all ranges?

[Martin Brubaker]

As for the touch screen, does it work better if you ground the unit?  The touch screens on my Siglent scopes seem to work just fine.

No, I haven't tried it. The point of a portable oscilloscope for me was precisely the lack of grounding and connection to the AC-line via Y-capacitors of power supply. A kind of cheap replacement for a differential probe... The task failed.

Was that 7% deviation on all ranges?

Yes.

Here is a picture of the modification.

[BillyO]

A kind of cheap replacement for a differential probe... The task failed.

Hantek make a reasonably priced differential probe.  Depending on your requirements it might do the job for you.

Just one final question.  I guess you took out one or more of the 3.3K resistors.  What values did you replace them with?  I can't see them in the photo.

Did you just replace the bottom one with a 3K?

[BillyO]

It's amazing that the designer used 1.24V instead of 1.18V when that is what is specified in the ADC datasheet.

I'm wondering if it's not the 2.46V across that divider that might be the erroneous value.

[Martin Brubaker]

Just one final question.  I guess you took out one or more of the 3.3K resistors.  What values did you replace them with?  I can't see them in the photo.
Did you just replace the bottom one with a 3K?

I did not remove the 3.3 kOhm resistors, it is much more convenient to solder a high-value resistor in parallel on top. I installed 33 kOhm on the bottom one (connected to ground). This is not shown in the picture. This is a photo of an unmodified oscilloscope, moreover, it is not even mine.

[BillyO]

Okay, I replaced the bottom one on Ch1 with a 3K and the situation is now much improved.  I'll proceed with Ch2.

See, this is what toys are for.   

[BillyO]

For Ch2 I tried Martin's suggestion of the 33K piggy back on the low side resistor.  It was a little quicker.  So Ch1 reads 2V and Ch2 reads 2.02V, so not too bad.  If you are handy with small SMD parts, have what you consider an appreciable error and are OCD, then you might want to do this little mod but keep in mind the risks.

[Martin Brubaker]

...and are OCD...

I'll add it. Be very careful with the power and fan connectors. They are SMD and are not attached to the board in any way except soldering. Be sure to hold the connector housing on the board when undocking.

[Grandchuck]

Sine wave at 1V, 1kHz sampled by a Focusrite Scarlet Solo and analyzed with REW.

The Fnirsi ARB generator is decent.

[JCS]

Hi All,
need help with the DPOS350P.

I've tried to connect the device via USB C to my laptop but my laptop does not detect the device. Any suggestion on what to do? Want to upgrade firmware but does not detect device.... Also, had the USB C cable connected whilst the device was ON and in the System/USB connect window. Nothing happens...

Also, the only way I found to charge this device via a USB C was by buying a USB C cable to 2.1mm DC jack and connect the 2.1mm DC jack to a 12V DC transformer. This works well and charged the device quickly.

Thanks,
JCS

[Grandchuck]

Try another USB cable.

Did your DPOS350P come without a charger and cable?

[JCS]

RESOLVED

I've tried a different USB cable and was able to do the firmware update.

SOLUTION:

For Powering the device - 12VDC normal outlet charger (@1.5 Amps output) with 2.1mm DC jack to DC Jack adapter (male to male) to DC Jack to USB C. This works well for charging.
For firmware update - Belkin USB A to USB C cable - detects equipment. I was able to update the firmware.

[csuhi17]

RESOLVED

I've tried a different USB cable and was able to do the firmware update.

SOLUTION:

For Powering the device - 12VDC normal outlet charger (@1.5 Amps output) with 2.1mm DC jack to DC Jack adapter (male to male) to DC Jack to USB C. This works well for charging.

I just received my DPOS350P, and discovered that it cannot be powered/charged by a regular USB-C Power Delivery adapter.

The oscilloscope is supplied with a ≈20W USB-A adapter that supports Quick Charge at 5/9/12V and a USB-A to USB-C cable.

It is beyond me how FNIRSI could decide to use a USB-C port for power, but fail to support the USB-C Power Delivery standard and requiring an adapter that supports Quick Charge at 12V.

They supply a suitable power adapter.  Also, it will run directly off 12V (tested) if you wish.  If you really wanted to use a PD supply, you can always utilize a PD decoy.  Sorry, but this is a "Meh!" moment for me as I'm not sure what the concern really is.

The REAL solution is to use the charger and cable that came with it.

And try reversing the cable, I remember from somewhere that they don't always solder both sides of the USB-C.

[svetlov]

[ptluis]

You're right, save your money. what you see is a lie, you can't trust measurements, fra, spectrum, etc its just a decoration gadget.
I bought one from amazon for 118€ and return it instantly after a few tests and the following video confirms my observations.

https://youtu.be/WtcAMw8iR7s?si=RJsOct8_PIymBPXC

[svetlov]

You're right, save your money. what you see is a lie, you can't trust measurements, fra, spectrum, etc its just a decoration gadget.
I bought one from amazon for 118€ and return it instantly after a few tests and the following video confirms my observations.

https://youtu.be/WtcAMw8iR7s?si=RJsOct8_PIymBPXC

let's give them another chance - after all, they chose the right vector of development of portable oscilloscopes in this model - after all, it combines almost everything that you wanted to see in such a device - the program code of the spectrum analyzer and frequency response analyzer needs to be corrected - but so far, none of the other manufacturers have offered anything similar in this budget - others, like Siglent, offer you to buy an additional generator for removing the frequency response, which costs more than this device - this industry needs a shake-up because many manufacturers have played too much, such as Owon, for example - after all, upstart companies like Fnirsi can shake up this industry - despite the fact that they play in a different price segment

[BillyO]

You're right, save your money. what you see is a lie, you can't trust measurements, fra, spectrum, etc its just a decoration gadget.
I bought one from amazon for 118€ and return it instantly after a few tests and the following video confirms my observations.

https://youtu.be/WtcAMw8iR7s?si=RJsOct8_PIymBPXC

That joker did everything he could to make it look bad.  I don't trust him any more than I do this scope.  Far better results have been published right here in this thread and in many other videos.  I mean who the f'k looks at a 10MHz signal with a 10ms/div sweep rate?  Give me a break!   

I'd like to see just one other device for $250 @ 350MHz that can do near as good, or do as much as this can.  Please show me. 

I know I can embarrass it with my Siglent SDS2354X+ any day of the week and twice on Saturdays, but that cost 12 times as much.