Do you trust in cheap handheld oscilloscope

So, i am finding a cheap oscilloscope, for hobby, not for professional using
Searching from many website gives me some model, the most popular is the DSO138, which is ridiculous cheap(less than 20$)
I’ve already order 1 DSO150(which has same spec)
So
The question is
How trustable are they, especially in modding light(maybe for measure pwm frequency, duty cycle)
And if my DSO turn out bad, should i get another handheld oscilloscope, but with high spec(fpga intergrated), or get the”real” big one

sure for flashlight applications
extreme accuracy or high frequency not required
most of the time flashlight stuff is all DC anyway
usually the pwm stuff isn;t done very often
a good DVM is more important than a good scope

alternately you could get a USB type scope, use with a PC

wle

I built a DSO138 last year (or was it 2015?) and played around with it some. It does work good but obviously is lacking a lot of features that the nicer units have.

For flashlight use it is ok though, it is enough to spot major issues but smaller things can slip though.

If you are trying to detect ringing for example it is iffy weather it will see it or not.

I love handheld oscilloscope, i can make a circuit and show my measure to friends anywhere(i am college student btw), a normal wont fit my backpack

Any idea about signal that’s lower than 100khz

How good are they for flashlight modding? Pretty OK.
For simple audio stuff? Still pretty OK!

Should you trust it for anything real? Nope, no way.

Trust seems like the wrong word for a scope, while in its oldest form its a very raw simple instrument, but in practice its easy to use it incorrectly and/or make bad assumptions about what you see. In the modern form, a digital scope, its fly by software regardless of how simple the circuits might be, so there is no way of knowing if some “feature” is showing something or hiding something of value.

My experience is that the chance of problems being user error vs issues with the scope are about 10 to 1, and not enhanced much by the quality of the scope.

Know how the scope works, what its limits are, how to use it, and what to look for in the signal and just about anything should be ok. Some like Fluke put a lot of smarts in the tool so they are simple to use, but that nice Fluke is like a grand or more, and very popular among those that use them in their work.

I use the word” trust” because manufacture can make the false claim(especially the cheap one)
2 mhz with only 1 MCU, no, i dont believe

The analog bandwidth do not have anything to do with the MCU.

I think it does, mcu if it is a low speed one, i dont think it can collect ADC fast enough to save in memory and display to lcd

Very true, not to mention the clock rate isn’t the same as the instruction rate, or the data rate, nor is the true operation real time.

Please refer to what I said before, not knowing how a scope works may lead to errors regardless of the quality of the scope.

Why would it need to?
Here you have a 25GHz scope with 1Ms/s: 30GHz sampling oscilloscope with TDR, CDR and optical option.
That is a analog bandwidth 25000 times larger than the sample rate (That type of scope need a very precise trigger to work).

maybe i misunderstand something here, but IMHO, i dont think only 1 MCU is enough for high frequency

You are misunderstanding, bandwidth on the input do not have anything to do with the MCU or sample rate. A scope may not sample as fast as the input frequency, instead it can sample in multiple scans and combine the samples to a curve (That requires the precise trigger I wrote about).