DS0138 (or DSO138)

[RAR2k]

I have just started testing a pre-soldered kit from Aliexpress bought with its clear enclosure for around 18€ including shipping.
At first I was utterly disappointed from
1) no instructions on how to assemble the enclosure. I could have guessed, but come on... then I found something online.
2) there was an offset (even in GND switched mode) of about 0.86V that I could not figure out how to clear. Online I did not easily find anything related to this issue on this model.
3) Probe calibration on the 1V setting was not possible as the edges of the square wave were still too rounded.

EASY SOLUTIONS
1) See image
2) click SEL several times until the left cursor that indicates your zero is selected, then old down OK! Voilà!
3) Replace C5 (1pF) with a higher value. 2pF was good for me. I added a 1pF in parallel on the bottom side of the PCB - now I can adjust C6 for the correct shape.
I will continue to test this gadget and see to what extend it can be used - I don't expect too much, but it might be helpful for minor projects.

 

[Tony Stewart]

If you expect us to know where you measured 0.86V on what device, then we expect you to figure it out on your own.

 

[Tony Stewart]

For 40 bucks you can get one with instructions assembled that works. https://www.ebay.ca/itm/12596534957...6822&msclkid=0e9b803b75661b72b893e4bc4e6b4b7f

a few had good luck with it https://www.amazon.ca/product-revie...r&reviewerType=all_reviews#reviews-filter-bar 200kHz BW ... its a creative design with too many cost reductions, not bad for 18€ including shipping.

 

[RAR2k]

If you expect us to know where you measured 0.86V on what device, then we expect you to figure it out on your own.

If I expected anything I would have stated it - this is the kind of reply that makes forums such a waste of time.
If you have a contribution that spans beyond your ego it would be appreciated, anything else you can keep for yourself. thank you.

 

[rjenkinsgb]

If you expect us to know where you measured 0.86V on what device,

The OP was explaining the initial problems with the kit (zero offset & frequency response) - and explained how to correct them.

It was a review / solution shared for others, not a question!

 

[Tony Stewart]

If I expected anything I would have stated it - this is the kind of reply that makes forums such a waste of time.
If you have a contribution that spans beyond your ego it would be appreciated, anything else you can keep for yourself. thank you.

I can't contribute wih your attitude. WTG on your fixes. Such an "utter disappointment".

FWIW, if you search for electronics by images, Google Bing et al are pretty useless.
Yandex.com works best.

Yandex

Finds everything

yandex.com

This led to the same offering for €3.06 but nothing useful on setup.

For those that are in EU.

Predaj Ds0138 ds0138 2.4 "tft-digitálne prenosné dimethyl acrylate púzdro" / Meranie a analýzy nástrojov > Bosch-kosice.sk

DS0138 DS0138 2.4

bosch-kosice.sk

 

[danadak]

Thats a lot of offset with probe input grounded needless to say.

Same thing can be said for rounded squarewave in its freq range, especially audio,
like 1 Khz.

Could the twos issues be inter-related ? You might, with input grounded, use a dmm
and look at input stage to the OpAmp follower, then at the PGA output. One stage at a time
to isolate whos hosing the signal path.

I built one several years ago, worked out OK. Useful really for simple stuff. There are folks who have done
dingle chip designs :

Configuring a PSoC as a DIY oscilliscope/logic analyzer - Part 1 - Embedded.com

Commercially available lab equipment like oscilloscopes, logic analyzers, and function generators are bulky and expensive, making them difficult to use

www.embedded.com

PSoC5LP: Oscilloscope, Logic Analyser, Signal Generator

Hi everyone, I found these articles http://www.embedded.com/design/prototyping-and-development/4421857/Configuring-a-PSoC-for-a-DIY-oscilliscope-logic-analyzer---Part-1...

community.infineon.com

http://web.mit.edu/pmagic/www/document/manual_v1_1.pdf

Regards, Dana.

 

[RAR2k]

I managed to correct the offset problem-
AV- is correctly regulated by the 7095 at -5.09V and R10 being exactly 3.00KOhm, so the offset must be caused on U2C V+ input. In any case, adding a 1K multiturn trimmer in series to R10 allows for quite a span of Offset correction. A lower valued for the trimmer would be enough, but that's what I had handy.

 

[RAR2k]

The assembly of the unit in the plastic case can be easier and more steady with spacer bolts and washers like this.
Adding a couple of washers underneath the board, It keeps everything tight together with the buttons and sliders sticking out just enough.
To me, without spacers the whole assembly is unstable and the controls are too lose.