AliExpress Gem of the Month - February 2025

A new month brings another confession. I seek forgiveness for spending numerous valuable Patreon euros on low-quality Chinese products. However, I have found something that might be intresting for all of us.

Those who have followed my work over the past six months know that I have gained extensive knowledge about TMC drivers and stepper motor tuning. I have translated most of these insights into best practices, implementing them into my TMC drivers within THEOS. These enhancements automatically configure the optimal parameters to extract maximum performance from the stepper motors.

However, there are certain parameters that cannot be optimized without closely examining the behavior of the coils themselves. Gaining insight into these parameters requires an oscilloscope, which for most of us who engage in fast 3D printing as a hobby, represents a pretty expensive investment. A quality 2-4 channel oscilloscope can easily cost between 500-700 Euros or even more for premium features. Since most of these advanced capabilities are unnecessary for our purposes, I was searching for a more affordable alternative and found this option here:

ZOYI ZT703S 3in1 Digital Oszilloskop / Multimeter / Signal Generator - Dual Channel - 50 MHz

So let me start with the bad things:

The Signal generator it's absolutely stellar—if your idea of fun is dealing with constant frustration. Seriously, it sucks! Just axe it from the feature list and pretend it never existed. You'll be doing yourself a huge favor and saving countless nerves in the process.

With that said let's start the review ;-)

At first, I was a bit skeptical due to its small 320x240 pixel display. I thought they might have cut corners on the hardware, making the user experience somewhat sluggish. However, the opposite proved true. The device boots in less than two seconds, everything feels snappy, and if you've ever used a scope, most of the user interactions feel familiar. For those who haven't, there is a manual written in good English, earning it additional points. But to be honest, I would rather watch 2–3 YouTube videos about using an oscilloscope and, especially, about how not to destroy your oscilloscope. :-)

As is often the case on AliExpress, many claims are exaggerated. While there might be a specific use case that justifies the advertised 50MHz bandwidth, in my practical experience, I can confirm that it performs perfectly up to 10MHz.

Additionally, they have implemented some convenient features called Measuring Modes, which automatically set your measuring cursors based on the scenario you select. For example, if you want to measure the duty cycle of a square wave, the Square Measure Mode automatically adjusts the resolution and positions the cursors correctly. I did not expect such functionality on an affordable device like this—thumbs up!

What about cheaper alternatives like the FNIRSI 138 PRO for 30 Euro?

While there are many other options available that may seem attractive at first glance, it's important to keep in mind that chopper frequencies can reach up to 250 kHz. Although it's technically possible to drive your stepper motors at these frequencies, doing so would significantly reduce their torque, making it impractical for most applications.

A useful rule of thumb is that your oscilloscope should have a bandwidth at least 10 times the frequency you intend to measure. This ensures accurate readings and maintains a favorable signal-to-noise ratio, especially as you approach the oscilloscope's bandwidth limit.

Cheap oscilloscopes, such as the 138 PRO and others, are often advertised with a bandwidth of 200 kHz. However, in reality, their effective bandwidth may be even lower. This limitation makes them unsuitable for our goals, as they cannot reliably capture the higher frequencies necessary for precise measurements.

Additionally, it only has one channel, making some measurements impossible and others more complicated. This is something beginners might not be aware of, but with some practical experience, you'll realize the importance of choosing an oscilloscope with at least two channels, and possibly more. Often, observing how one component behaves can provide valuable clues about potential circuit issues. Being able to measure a second point and see the relationship between two signals is crucial for diagnostics. While having a third and fourth channel can be beneficial, in my opinion, the advantages diminish compared to the addition of a second channel.

So in conclusion you get a wonderful mobile 2-in-1 oscilloscope and multimeter (we dont speak about the signal generator) with and internal bettery that is USB rechargeable for around 75 Euros with all tools you need, two decent oscilloscope probes, two reliable multimeter probes. You can get the osziloscope from the link below:

https://s.click.aliexpress.com/e/_onnTaTf

Combine this with the SpreadCycle tuning guide from AnalogDevices and you have all the neccessary tools to understand what you TMC Drivers do and how to optimize it for your goals! You find the guide for thos here:

https://www.analog.com/en/resources/app-notes/an-001.html

In Conclusion

You receive a good mobile 2-in-1 oscilloscope and multimeter (we dont speak about the signal generator) with an internal battery that is USB rechargeable, all for around 75 Euros. The package includes two oscilloscope probes (check that you get the upgraded version) and two multimeter probes—everything you need. You can purchase the oscilloscope from the link here: https://s.click.aliexpress.com/e/_onnTaTf

When you combine this with the SpreadCycle Tuning Guide from Analog Devices, you'll have all the necessary tools to understand how your TMC drivers function and how to optimize them for your specific goals. You can find the guide here: https://www.analog.com/en/resources/app-notes/an-001.html

P.S.: I focused mainly on the oscilloscope functionality, but what I can say about the multimeter function is that it works just as intended. You can measure voltage, current, resistance, capacitance, and more. There’s nothing particularly special, but also nothing missing—a perfectly good experience. I even double-checked it with my regular multimeter, and the ZOYI measurements were spot on. So, no complaints here!