When it comes to standard equipment for the electronics hobby, everybody and their neighbors list an oscilloscope as a necessary tool to have. I’ve been on the fence about getting one, however. I can absolutely see it’d be useful for some tasks; however, I’ve never run into a situation where I particularly needed one yet. I’m sure that day will come but that nevertheless has held me back from actually buying one. That, and, of course, the hefty price tag for oscilloscopes: most oscilloscopes that are considered “beginner” or “hobbyist” still cost around 300 euro. Recently, I ran across the DSO138mini by JYE Tech that seemed like a perfect midway solution.
The DSO138mini has many people divided on the topic of its quality. If you search online for just that tag, you’ll find an equal number of people writing vehemtly on how it’s an absolutely waste of money as you’ll find people saying it’s a perfectly serviceable little toy for 30 euro. I figured to buy it as exactly that – thirty bucks worth of soldering practice that ends up with me having a handy little oscilloscope that does very basic things. That way, I figure I can also get experience using an oscilloscope for some tasks as well as learning what situations I could use an oscilloscope for. I figure that by the time I run across more situations where I’d need a real one, then that’ll be the time I invest in a solid beginner’s scope.
When I started assembling it, I figured I’d document the journey. Very quickly, though, I realized I’d gotten into the flow and had so much fun soldering that I’d forgotten to take pictures in the meantime! So, well, here’s a very incomplete set of photos of the construction:
The components with the manual 
The loose clutter of components to be soldered 
The main board 
The LCD board 
As a first test, you have to power just the LCD. Success! 
Soldering the components did take quite some fiddling 
These resistors had slightly different color coding than I was used to 
These are just the resistors! 
It was quite a neat solder 
Basically, after the resistors, I’d forgotten to snap pictures, so here’s the oscilloscope at the testing stage.
When the build was complete, I ran into an issue testing it. As you can see in the last picture in the gallery, the result seems to be maxed out. What should be visible is the top of the signal about three squares away from the center (each square should represent 0.5V, and the signal is supposed to be around 2.5V). The other issue I ran into is that I’m supposed to be able to adjust trimmer capacitors to make the wave nice and square. Right now, you can see that the vertical lines go down in a slope, rather than straight down. However, no matter how I’ve been trying, I haven’t been able to adjust the trimmers easily. When I try to move them, my screwdriver slips and it seems as though I’m ruining the screw in the trimmer.
As I retested the resistors, I see it might be resistors R2 and R4: R2 should be 1.8M Ohm but it’s 1.5M Ohm; similarly, R4 should be 2M Ohm but it’s 1.8M Ohm. I’m totally guessing, but that might be the reason why the waveform is too high. As for the trimmer capacitors, I have no idea why they’re so hard to adjust. I’m probably going to post on Reddit as well to see if somebody has some advice.