[solved] Smartphone as oscilloscope

[Daniel Perez LW1ECP]

Hello! Many electricians cannot justify the purchase of an oscilloscope. However, from time to time it is interesting to be able to check for distortion in a current. There are several articles that suggest using the MIC input on a smartphone, and an oscilloscope app. Success largely depends on the phone model, e.g. its low-frequency response, ALC characteristics, etc.
On my Samsung A01 (SM-A015M), after 50s of using the sound recorder or filming, an ambient noise reduction kicks in, as if it had been analyzing the spectrum during that time and then calculates the filters. This also happens during scope usage, obviously a no-no. The manual and web results don't say how to turn it off. Does anyone know how? Thank you!

[ebclr]

https://www.instructables.com/Raspberry-Pi-Pico-200Khz-Digital-Oscilloscope/

[Doctorandus_P]

The trouble with most of the hobby projects is that almost every time it's just a bit of software without even attempting to build some decent frontend for the scope.

I bought myself a jye-tech DSO Shell (clone?) for about EUR30, and it is somewhat usable (Get the version wit the rotary encoder) but the LCD has a quite low resolution, it has low bandwidth and the "triggering" is quite bad too. I mostly think of this as an STM32 development platform with LCD instead of an oscilloscope.

Then there is the "DSO Nano" Which I consider far to expensive for what it does. It's just too close to the price of a "real" scope to consider buying and it does not have a decent user interface.

Even though I already got a (quite old) Rigol DS1052E myself, every now and then I think about buying an Hantek 6022BE (or 6022BL (with logic analyzer)) It's cheap enough to buy just for fun (for me) and I've read and seen some reviews about it and it seems to be about the minimum hardware that has enough performance to be actually usable. It also has two channels, which I also consider the minimum. You need tow channels for a lot ofmeasurements, such as comparing input and output signals of a circuit or measuring phase shifts. It is a PC based USB scope, but if you really want to keep the price low, not having to pay for additional LCD and buttons is probably a good thing. Apparently OpenHantek works better with it then the original software, and there are also some other programs written for it, including something for android. You can have a look at the internals on: https://sigrok.org/wiki/Supported_hardware

[tepalia02]

Hi, did you give this a try?
https://how2electronics.com/diy-smartphone-oscilloscope-using-raspberry-pi-pico/

[Daniel Perez LW1ECP]

Thank all of you suggesting the raspberry pi pico. I am an electronics engineer, I already own a 100MHz CRT scope, a DSO Quad, and use a Tektronix TDS3032 at work. Eventually I used the PC sound card to view waves.
The target of my post is non-electronics people, who think "I've never needed an oscilloscope to do a correct job" and so aren't interested in spending on something they feel they don't need. And of course DIYing it is not of their profession.
But I've recently shown a (professional, very capable) electrician how harmonics and cos(phi) look on a screen, and he opened up his eyes. "All my life I had seen these things only on textbooks!". He had been working with power factor correctors, harmonics filters, and doing that well, but blindfold.
That's why I bet with just a handful of resistors and some Android tweak, these people will be more confident in why they are doing what they are doing.

[Haenk]

Is that a good idea, blasting your expensive phone with unknown signals?
If you are building something to protect your input, and maybe even a level selection, that will cost money. End-user-ready it will certainly be at the same price range as those cheap chinese mini-scopes. Plus the mini-scope might be blown up - but your expensive phone remains unharmed.

[themadhippy]

Many electricians cannot justify the purchase of an oscilloscope

Really? whats a scope cost? Compare it to the cost an average MFT, money aint really the object,the object  is  your average sparky has no need for a scope.

[Daniel Perez LW1ECP]

Many thanks for all the replies. I made up my mind, a more realistic approach is to show electricians what can be done with a scope or a scope adaptor, and let them decide if it is worth buying.
Anyway, please let me go off topic to explain my backgroud, trying not to touch politics. As I have already mentioned, here typical salaries are half those in US or EU. And any imported instrument ends up costing twice after accounting for import taxes and importer profits. On top of that, we individuals have no easy access to dollars, we are forced to buy them in the black market where they cost twice as stated by the government. The result: purchasing any import "hurts" our pockets  eight-fold as if in the Northern hemisphere.
Finally: I have other reasons to deactivate the noise reduction: it is just annoying in my videos, I prefer background noise without being suddenly replaced by weird acoustic artifacts at some point. Perhaps a more suitable place is an Android forum.
Best regards!