Measuring instruments are an important part when working with electronics. They’re essential for gaining insight into how a circuit works (or why it doesn’t). The most important tool is usually the multimeter: it allows you to measure voltage, current, resistance, and capacitance. Sooner or later, however, you’ll encounter signals that change so quickly that a simple multimeter isn’t enough. In those cases, an oscilloscope is needed.
Good oscilloscopes are expensive – even basic entry-level models start at around $400. However, in many cases, a simple device is enough. The Zoyi ZT-703S shown here is an affordable, portable oscilloscope that’s perfect for beginners or as a mobile tool for a quick look at a circuit.
You can find the German version of this review on my website: SammysHP Blog › Zoyi ZT-703S
The device was provided by the manufacturer for this review. Thank you very much!
Overview
The oscilloscope comes in a large box with all the necessary accessories, so you can get started right away:
- Oscilloscope probe 60 MHz 10x/1x with accessories
- Test leads
- USB-C charging cable
- Manual
- Pouch
The manual, enriched with many pictures and explanations, provides a good overview of the functions, though you can figure out a lot by experimenting on your own. The pouch is basic but serves its purpose. With all the accessories, however, it does get a bit tight inside.
The ZT-703S is a handheld device, similar to what you’d find with digital multimeters. The case is made of two components: a rigid black plastic (ABS) that’s overmolded with a softer red plastic (TPE). Overall, the build quality feels very solid. The only downside is that the display is fairly easy to scratch.
Measuring 177 × 89 × 40 mm, the ZT-703S is surprisingly compact for its features and is roughly comparable in size to larger multimeters. It weighs 391 g, making it ideal for portable use.
There is a folding stand on the back of the device that allows it to be tilted at an angle of approximately 45°. The 320 × 240-pixel display, measuring roughly 3.2″ (81 mm) diagonally, is easy to read from any direction.
Hidden behind a cover on the right side is a USB-C port. This is used not only to charge the built-in battery but also to perform firmware updates and to download screenshots.
Speaking of the battery: the device uses a standard 18650 Li-ion battery with a capacity of 3400 mAh in a regular battery holder. This makes it easy to replace (once the case is opened).
There are only a few dedicated buttons for operation. Most functions are controlled via softkeys on the display (F1 to F4) and through menus using the navigation buttons. The power button has a red backlight, but it’s used solely to indicate the charging progress.
Oscilloscope
The main feature of the ZT-703S is its oscilloscope function with a bandwidth of 50 MHz. However, expectations should be kept realistic: this isn’t a professional-grade instrument, but rather an entry-level model with basic functionality, available for around $65. That said, especially for mobile use, it often performs very well for quickly getting a first look at a circuit. For beginners, it might even be sufficient as their only oscilloscope.
The ZT-703S has two channels. The BNC connectors are located at the top of the device, slightly hidden to protect it from mechanical damage. This design has a small flaw: the recessed placement makes it somewhat awkward to lock BNC connectors in place – and some plugs won’t fit fully due to the limited depth. If you have access to a 3D printer, you can print an alternative case insert that solves this problem.
The user interface is simple to understand, especially for those who have used an oscilloscope before. The status bar at the top of the screen displays the operating mode, acquisition window, time base, trigger settings, and battery level. At the bottom, you’ll find indicators for the selected sensitivity and function generator, along with the menu’s on-screen softkeys.
There are two main menus, which you can switch between with the Menu button. The first menu assigns functions to the cursor keys, with the on-screen softkeys color-coded to match the selected channel. The second menu provides access to the device’s settings. You can scroll through the individual pages using the left and right navigation buttons.
When “VOL/TIME” is selected, the cursor keys are used to adjust the horizontal (time) and vertical (voltage) scaling. The time base can be set in fixed steps ranging from 10 ns/div to 20 s/div. At 200 ms/div and slower, the oscilloscope automatically switches to rolling mode. An XY display mode is also available. The voltage sensitivity can be set between 20 mV/div and 10 V/div. Neither the time base nor the sensitivity supports variable (fine-tuned) values – only fixed increments are available.
The “MOVE” function allows the plot of each channel to be shifted both horizontally and vertically. Holding down the F2 button centers the waveform vertically, while pressing the MENU button centers it horizontally.
The oscilloscope offers the standard trigger modes: Auto, Normal, and Single. Triggering can be set to either the rising or falling edge of the signal. The “TRIG” function allows you to adjust the trigger level. A handy feature: if you hold down the button, the trigger level is automatically set to half the signal’s amplitude.
The last function in the first menu allows you to move the cursors. You can display either two horizontal cursors, two vertical cursors, or both pairs at the same time. However, only the difference between the two cursor positions is shown – the absolute values of each individual cursor are not displayed.
There are eight basic measurement functions available; up to four can be enabled at the same time: Vpp, Vmax, Vmin, RMS, FCNT, Duty, Period, and Freq.
At the cost of higher power consumption, the “High Speed Mode” increases the sampling rate from 200 MSa/s (“up to 30 MHz”) to 280 MSa/s.
The ZT-703S also features two function generators: the simpler one generates either a 1 kHz square wave or square, sine, and triangle waves with a frequency adjustable in seven steps from 10 Hz to 5 kHz. However, if anything other than the 1 kHz square wave is selected, the time base is limited to 100 µs/div.
The second function generator can only be used exclusively, as it takes up the full processing power of the microcontroller. While it offers some additional settings, its overall functionality remains fairly limited.
In both versions, the signal is available through the port on the right side. Overall, the function generator is more of a small gimmick. It’s probably most useful for compensating the probe.
The FFT function is hardly worth mentioning. While it does display a spectrum, it lacks any labels or adjustable settings, making it practically useless in real-world use.
In some situations, various problems occur related to the trigger point and data acquisition. Several issues have already been fixed in the current firmware version 1.5.7, but not completely. Visual artifacts still appear when scrolling the view at certain scales, and capturing signals below 250 ns/div remains problematic. Hopefully, Zoyi will address these issues in a future update.
A big advantage of battery-powered oscilloscopes is that they aren’t grounded. This means the ground can be connected to a different potential (but be careful: other parts of the scope like the other BNC connector will also be on the same potential!). This feature helps to avoid ground loops. And of course, the portability is a huge plus, especially when working on large machines.
Unfortunately, the basic operations like Add and Invert, which would allow combining the two signals, are missing. Also, displaying the actual cursor positions, rather than just their difference, would be very helpful in my opinion. The FFT function, in its current state, isn’t practically usable. It either needs a complete overhaul or should be removed altogether to make room for more useful features.
Multimeter
In addition to its oscilloscope function, the ZT-703S is also a full-featured multimeter. A quick press of the Mode button switches to DMM mode. The selected setting is remembered after a restart. It can measure voltage, current, resistance, capacitance and frequency – with up to 25,000 counts! There’s also a fast-responding (latched) audible continuity tester and a diode test function.
Below the large display of the real-time measurement, the minimum, maximum, average and – if applicable – frequency of an AC signal are shown. The top third of the screen is taken up by a simulated analog meter. It updates three times per second, together with the digital readout, which feels a bit too sluggish in my opinion.
Relative measurements and a display hold function are also available. The measurement range is set to auto by default but can be manually adjusted if needed.
Below the buttons are the four 4 mm ports for the test leads. They have the standard 19 mm spacing, making them compatible with accessories from other manufacturers.
A sticker on the device at delivery warns you about the correct use of the ports. Additionally, when switching to current measurement mode, a corresponding warning appears on the display. While this doesn’t replace active monitoring of probe connections, it’s still better than having no warning at all.
The supplied test leads are basic but functional. The 90 cm long cables, with an outer diameter of 3.5 mm, feel a bit stiff.
The probes are 22 mm long and taper from a 2 mm diameter at the rear to 1.2 mm at the fine tip. They can be protected during transport using the included caps.
Conclusion
It’s hard for me to give a final judgement. The Zoyi ZT-703S offers many basic features one expects from an oscilloscope. With two channels and a 50 MHz bandwidth, it should be suitable for a lot of applications. Additionally, it doubles as a multimeter with 25,000 counts. The battery operation and compact design make it an ideal companion for mobile use.
However, the quality of some functions leaves something to be desired. Various bugs complicate usage or sometimes make meaningful measurements impossible, as it’s unclear whether the issue lies with the meter or the device under test. The function generator and FFT function are barely practical in real-world use.
That said, the device is by no means unusable. For many applications it will be perfectly sufficient, and the low price makes it especially attractive for beginners. Still, I believe much more could have been made with the given hardware.