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Friday Teardown: Logitech Unifying USB Dongle

The hope was that I would be able to compare a Unifying dongle to a Pre-Unifying dongle.

So here a new type of post I'll be trying to do here on the regular: Friday Teardowns! Every week I'll find some interesting device or gadget in my possession and take it apart, figuring out what makes it tick.

Without further ado, here is this week's first teardown: Logitech wireless mouse USB dongles.

What Is Unifying?

For the uninformed, Unifying is a system that allows multiple Logitech devices to painlessly and seamlessly connect to a single USB dongle. Each dongle is capable of communicating with up to six devices at the same time, reducing the number of dongles that need to be connected a computer. When you have a small amount of USB ports, like with a laptop, less dongles mean more USB ports available.

They also mean that you have one less device that you need take with you. Logitech unifying receivers are small enough that you can plug and forget, leaving the unifying receiver in the computer for the life of the Logitech devices connected to them. No more forgetting a dongle somewhere and having its accompanying device become a paperweight.

Show Me Your Secrets

Going into this teardown, I thought I was actually taking apart a Logitech mouse dongle that predates Logitech's Unifying dongle system. The hope was that I would be able to compare a Unifying dongle to a Pre-Unifying dongle.

Using pliers to snap off the black casing on both the "pre-unifying" and the known Unifying dongle, we get our first look at both devices:

Left: "Pre-Unifying" dongle. Right: Known Unifying dongle
Left: "Pre-Unifying" dongle has no Unifying symbol. Right: Has Unifying symbol.

Looking at both devices, we see that they are both similar in layout. Both have an off center QFN package that are surrounded by passives (capacitors, resistors), with the one right having around 10 more than the left. At the top of the dongles, a zigzagging PCB trace acts as the antenna for the 2.4ghz signal to the wireless devices.

On the opposite side we find both have a Quartz Crystal (Silver Rectangle) with some more passives. I was unable to find any information on the frequency of the Quartz Crystal, but it is likely 16mhz given the identification code on the package and the fact that many common microcontrollers run at 16mhz.

So all in all, both devices are extremely similar. I was not expecting them to be so close in design, since both were supposed to be using different protocols, and were around 5 years apart in age. At this point I realized something was off and began to do some more sleuthing.

To The Internet!

My first thought was to begin by looking up both dongles in the FCC database. The FCC database contains information on every electronic device sold in the United States. It includes application information, photos and more.

According to the internet the FCC should be located on the outside of the device in the format xxx-xxxxxxx. However, on our device we see nothing that seems to resemble the required format. Attempts to search with these IDs fail.

Instead, I start a new search, this time with "Logitech FCC ID". Scrolling down the list of results I notice a result "FCC ID JNZCU0014 2.4GHz USB Transceiver by Logitech"

This takes me to a page filled with FCC information on some random Logitech USB Receiver. But what caught my eye with this result was the ID, JNZCU0014. On our own device, we see a similar string of letters, CU0007. So now I search for "Logitech FCC ID CU0007". Bingo

https://fccid.io/JNZCU0007

So now we're on a website with the FCC information we're looking for. It was submitted for FCC approval on January 08, 2010. Looking through the submitted documents we find some external photos:

Wait a minute, is this the right device? There's a Unifying logo on this dongle. But on our device, there is clearly no Unifying logo. Maybe it got rubbed off? At this point I was confused. The submitted user manual on that page is for a Logitech M705 marathon mouse, which clearly has support for Unifying, and which I have never owned, so maybe I got the wrong FCC ID.

Time to try something else.

Datasheets Are Your Friend

At this point I decide maybe I can figure this out by looking up the datasheets for the microcontrollers on each of the dongles.

The "not Unifying" dongle has NRF-LU1PA stamped on it, which is a Nordic Semiconductor nRF24LU1+ OTP.

The known Unifying dongle is a Texas Instruments CC2544.

These two chips are 8-bit microcontrollers based on the Intel 8051 microcontroller first released in 1980. Derivatives of this original microcontroller remain in popular use due to their availability, cost and low power efficiency. Both have a 2.4ghz transceiver and USB controller built into them, making them a good choice for applications that require as little supporting components as possible.

With this information, we can determine that both devices are extremely similar, using microcontrollers with similar feature sets, architecture and board layout.

Did I get it wrong and this is actually a Unifying receiver?

The small QFN microcontroller package on both Logitech dongles require little supporting components, allowing them to fit within the space of a USB connector. Dime for scale.

To Wikipedia!

While searching up information for the known Unifying receiver, I landed on the Wikipedia page for Logitech Unifying Receiver. The first line caught my eye:

"The Logitech Unifying receiver is an extremely small dedicated USB wireless receiver, based on the nRF24L-family of RF devices"

So according to Wikipedia then, this dongle should be a Unifying dongle, more-so than the actual Unifying dongle that uses a Texas Instruments chip.

On that same page there are lists of devices, including device names and their accompanying USB ID. So let's plug in our mystery dongle and get to the bottom of this:

VID_046D&PID_C52F is the information we're looking for. This is our USB ID.

According to device manager, our USB ID is 046D:C52F….which is not on the list. So this isn't a Unifying receiver? Or is it? At this point I'm stumped by all the conflicting information I've gathered.

More Sleuthing

Next I decide to google the USB ID. The first result is the Logitech M320, which is a currently sold Logitech product…and has Unifying. The page confirms the USB ID…so I don't even anymore.

Amazon

Nearing the end of our story, I now turn to Amazon in the hopes that I bought this mouse there, as I had forgotten the exact model of mouse I bought. I had thrown away the mouse after it broke several years ago, but kept the receiver.

According to Amazon, I purchased a Logitech M310 on July 6, 2010. I had purchased this mouse to go with my then newly purchased Toshiba Laptop.

Next we head to the questions page and type "Unifying". And we get our answer

It is not a Unifying dongle. Instead it is a USB dongle that only connects to the mouse it comes with. This explains the lack of Unifying logo on the casing of the dongle. So why does a lot of information such as the FCC data and USB ID point to this being a Unifying device?

Speculation

The M310's dongle, being nearly identical hardware-wise to the known Unifying dongle, likely is a Unifying dongle. It's just missing the required firmware that gives it the Unifying capability.

At the time I bought the M310, Logitech's Unifying receiver system was less than a year old, having from the best of my knowledge, been first shown to the public in August of 2009. By selling their cheaper devices without Unifying, Logitech could push consumers to more expensive devices that included Unifying, allowing them to pay for the R&D costs of Unifying. Reusing the Unifying hardware on their cheaper devices meant they didn't need to design a specific dongle for them, keeping prices low. They just flashed different firmware with Unifying disabled for the cheap devices and called it a day.

Today, the vast majority of Logitech's mice lineup come with Unifying dongles, including many of their budget options.

Conclusion

As a final data point, if we insert the dongles into a computer, Windows will tell us the names of the devices:

So in the end, we have two dongles, both are Unifying devices hardware-wise, but each is running different firmware.

As an aside, I do find it interesting how little the dongle design changed over the course of a few years. Logitech changed supplier for their microcontroller, but the architecture and board layout pretty much stayed the same. I did quick check with a flashlight down the USB plug of a third even newer Unifying receiver that came with an MX Master. It showed that over the course of 6+ years, the design has not changed much. (I did not tear down the third one).

Outward appearance changed over time, but internals remained the same.

Optional Side Quest: drink every time I typed "Unifying" in this blog post. I am not responsible for any cases of Alcohol Poisoning.

Thanks for coming along with me on this ride.

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