TC66 (C), a USB tester with a USB Type-C connection and a built-in trigger for various protocols

Back in winter, news came out that RuiDeng was planning to release a new USB tester. I was particularly interested in this model, and now I have one in hand to test.
This review covers the tests, as well as why this particular model caught my interest.


First, let me explain why this model is interesting.
RD has released many different tester models. I think you’ve seen reviews of them, since there was a whole series of different models, but they all had a couple of things in common that I didn’t like.
1. No dedicated ADC, which means lower measurement accuracy. In practice, it wasn’t much better in this respect than its less expensive siblings.
2. It showed information about the charger’s control protocol, but offered no way to control it.

Both of these issues have been fixed here. The tester now has Type-C connectors only, so in some ways it’s less versatile. On the other hand, with more and more devices using this connector, this model is more of a “future-proof” choice.


Specifications claimed by the manufacturer.


It comes in a plastic case, which is packed inside a foam box. When I picked up the parcel at the post office, it felt empty because the tester is so light.


First impression: small—I’d even say very small.


The dimensions, in more familiar units.


And compared with a standard matchbox and the testers I use for work.


1, 2. A small display on top; labels for the controls and connectors on the bottom.
3. Two control buttons and two switches on the top edge.
4. A microUSB connector on the bottom edge.
5, 6. USB Type-C input and output connectors on the short sides, respectively.


A - Button for changing a parameter value or opening a submenu
B - Menu navigation button; press and hold to activate the selected item.
C - Switch for power from the USB Type-C connector. When switched off, the tester can be powered via microUSB to improve measurement accuracy and extend the voltage measurement range (almost down to zero).
D - Power Delivery (PD) control mode switch. In one position, the tester controls power delivery; in the other, the load does. So without a load, it will work in only one of the modes.
E - External power connector.


Power it on, and the first distinctive feature of this model becomes apparent: it can measure current in both directions, not just from input to output. Other tester models could measure only voltage in reverse mode. The arrow indicates the direction of current.

The screen is small, but bright and high-contrast. It has a protective film, which doesn’t get in the way.


Bidirectional measurement is useful and is promoted as a feature of this model. If I’m not mistaken, the ZY1276 can do it too, but both testers have the same problem: when measuring in reverse (from output to input), they add their own current consumption—around 20 mA, depending on display brightness—to the reading. In my opinion, the programmers could have added a correction, but they didn’t. So for accurate current readings, connect it the right way round (input to output), or power the tester from an additional power supply.


Example of the display with no load in both modes.


While I’m at it, I’ll check its current consumption. It’s almost independent of the operating mode: 17 mA with the backlight off and 26 mA with the backlight at full brightness. It doesn’t depend on the input voltage at all.


Operating modes.
1. Measures voltage, current and temperature; calculates capacity, resistance and load power. Resistance and power are calculated mathematically from the voltage across the load and the current in the circuit.
2. Logger mode: saves measured parameters to memory.
3. Measures voltage, current and temperature, as well as the voltage on the USB data lines, and identifies the charger’s control protocol.
4. Control protocol analyzer. In this mode, the device can check which protocols the charger supports.
5, 6. Manual control mode. Here you can select the required protocol and, if the charger supports it, activate it manually.


Control menu.
1. The menu is long. Press the right button to move between items, hold it to select an item, use the left button to change a setting, and hold the right button to exit.
2. Delay before the display automatically dims. I had it set to 9; even after a long time, the tester only tried to dim the display once, then brightened it again.
3, 4. Manual brightness adjustment, 10 levels.
5. Temperature in degrees Celsius or Fahrenheit.
6, 7. Enable USB and Bluetooth communication (for the model with the C suffix).
8, 9. Rotate the image, 180 degrees only.
10. Force the CC pin pull-up when operating in Power Delivery mode. This is needed in some situations when charging devices through the USB tester.
11. Language: English/Chinese
12. Reset all settings.


More display modes.
There is also a simplified display mode showing only voltage/current/power.
The last item shows the firmware version and total operating time, the so-called “hour meter.”


Screen switching sequence.


The internals, of course.
As usual, the case is very simple: a board with the display and electronics, plus a couple of decorative covers. Unfortunately, manufacturers rarely make proper enclosures for their instruments, which is a shame.


They did at least add protection around the display, though the components themselves are still “unprotected.”


The layout is very dense, which was to be expected: fitting all the components into such a small space is no easy task.
Overall, the assembly is neat. The Bluetooth module is visible at the bottom left. As far as I can tell, it simply isn’t soldered in the cheaper version, so you could solder it in yourself if you wanted. I’m not sure, though, since the firmware may also have this feature locked out.


A little more detail on the components.
1. The microcontroller that runs the whole thing.
2. A 256 Kbit (32 KB) EEPROM, presumably for storing accumulated measurement data. The firmware is unlikely to take up that much space, and storing it in external memory probably wouldn’t be convenient anyway.
3. Dialog Bluetooth module
4. A 15 mΩ current-sense shunt installed in the power rail.
5. The shunt signal is measured by a dedicated ADC, the INA226, which is designed for this kind of measurement and has a maximum error of 0.1%, as well as a Uoffset of just 10 µV. This chip also measures voltage. One notable feature is that the current-sense shunt can be installed in either the ground rail or the power rail. The ZY1276 tester uses the same chip.
6. The chip marked PBAC, as in the ZY1276, presumably handles the Power Delivery function.

The internals are very similar to the ZY1276, which is a big step forward compared with the UM24C series and similar devices, where the microcontroller handled all the measurements.


Since this device is, to some extent, a measuring instrument, how could I skip checking its accuracy? After all, that’s one of the key differences between this model and its predecessors.

The device starts up at around 3.15 V, although the display barely lights up. The ZY1276 starts at an even lower voltage, though not by much. And although the voltage is clearly below the regulation threshold, the measurements are excellent. In general, voltages below 3.5–4 V should be measured with power supplied by an external power supply, which is one reason the microUSB port is there.


Tests from 3.18 to 27.5 V: in short, the results are very good. Some readings are a little better, some a little worse, but overall they’re solid.


Current measurements also show a small error, but in my opinion it’s not a big deal.
In the last two photos, the ZY1276 reads slightly high because I had to switch the auxiliary power over to it, so it also started measuring the current drawn by the second tester.


When automatically detecting charger protocols, the only one it failed to identify was QC at 20 V—or, to be more precise, above 12 V. In this case, though, that’s a “quirk” of the charger, not the tester.
The Huawei protocol detection also occasionally failed. What’s more, when I tried to detect Huawei SCP mode, the tester usually rebooted, so I had to run the tests with auxiliary power.
The ZY1276 behaved more consistently and reported a similar list of supported modes. Unfortunately, in QC2.0 and QC3.0 modes, manual selection is also limited to 12 V.


The standard modes are straightforward: select a protocol, open the controls, and choose a mode. Power Delivery is a little more complicated.
You need to enter trigger mode, then move to the PD line. After you select it, the tester will ask you to reconnect it. Once reconnected, you can manually control the Power Delivery modes. By the way, you can easily select 20 V from the same charger here.


I'll wrap up the tests with a look at the software for computers and smartphones.
To download the relevant software, either follow the link or scan the QR code on the packaging.

The computer software installs without any problems, but after launching it, it couldn't see the tester until I selected driver installation mode.


Once the driver was installed, the software found the connected tester on its own and started displaying the voltage shown on it, even though I hadn't pressed the Connect button yet.
The software has a Firmware update tab. When I opened it, I found that a new version was available, but when I tried to update, it gave me a hard time.
In short, to enter firmware update mode, disconnect all cables from the tester, hold down the left button, then connect the interface cable. The screen will indicate that firmware update mode is active; only then should you open the update menu.


After you click Update now, the software takes care of everything. Once the update is complete (about a minute), the tester returns to normal operation.


Click Connect and the software switches to normal operation.
The software is very simple. There are a couple of buttons on the right: one mode shows what's happening now, and the other lets you view what's stored in the tester's memory.
The large area in the center displays current and voltage graphs.
There are three buttons at the bottom. The first and third change the tester's display modes, essentially doing the same thing as a single press of the left and right buttons. The middle button rotates the image on the tester by 180 degrees.
And that's about it.


A few words about the data logger mode.
When cycling through the display modes, you'll find a screen marked REC. Press and hold the right button to open the settings and start recording. Available settings:
Start/stop recording
Measurement interval: 1–60 seconds.
CE — clear memory.

The screen also shows the recording time and the percentage of memory used. At one sample per second, one percent corresponds to 14 seconds, so it takes 1,400 seconds, or 23 minutes, to fill the memory. If you select a 60-second interval, the memory will last for 23 hours.


Click Offline data to access the recorded data, which you can view as a graph or save to a file.


The smartphone/tablet software is even simpler. There's no access to recorded data or firmware updates, but otherwise it's the same.
You have to connect to the tester from within the software; a regular search/connection attempt won't work.


So, what do I think of this tester, especially compared with the ZY1276?
The big step forward is the use of proper circuitry: the manufacturer has finally decided to use an external ADC.
It can now do more than just monitor charger control protocols; it can also control the modes, and the manufacturer has even added Power Delivery support.
In essence, this is a simplified version of the ZY1276, but the simplification is in the software, not the hardware. The TC66 has the advantage of easier firmware updates: the ZY1276 requires a programmer, as well as software that has its own quirks.

The only thing I find inconvenient is that it has only USB Type-C connectors. The ZY1276 is more versatile in this respect, since it also has the more familiar USB-A ports. However, connecting Type-C requires a Type-C male-to-male cable. Since I don't have one, I couldn't test Power Delivery control with the ZY1276.

Otherwise, my impressions were positive: good accuracy, a reasonable set of features, a standalone data logger, trigger mode, compact size, current measurement in both directions (with a caveat), a reasonable price, and a Bluetooth version available.

That's all from me. I hope you found the review useful. I probably forgot to mention something, so if you have any questions, ask away and I'll do my best to answer.