Looking for a back cover for a Logitech R400 wireless presenter I stumbled upon the crazy world of R400 presenters. They can be found for around €4 on Ebay or Aliexpress and many other sites. They look very similar to the classic Logitech R400. Since they look so similar I decided to buy a few to test them out... Maybe the back cover would fit the original one too...

Looks

Front:

Pretty similar. No logos on the fake one of course. The fake one lights a tacky blue LED if you press a button. The buttons feel spungy and disconnected. The Logitech device has a nice frosted plastic light guide whereas the fake one uses a clear one. Frosted plastic is the winner here.

Backside:

Left is the fake device. The only major difference is the warning label which is properly silkscreened on the real presenter as opposed to the fake R400 which is a sticker.

Internals

So similar, yet so different. Left is the fake one. The molding is bit neater on the real one, less routing traces.

The chipset used in the Logitech one is the CYRF6910-340LFXC. It is a 40-pin QFN chip. The PCB also has a proper powersupply based on two IC's. One is housed in a SOT23-6 package, the other seems to be an SC70-5. It is a boostconverter outputting 3.3V. You can clearly see that this PCB is made for testability and debugging judging the amount of testpins found. Since the radio IC used is a generic 8051+RF chipset it also requires a programming port.

The fake device is built around a SOIC16 device with only the marking L1651bT or L16516T on it. There is no powersupply to be found which means that the laser brightness is depending on the amount of power still left in the batteries.

Workings

The fake R400 seems to work just like the real R400. The major difference is that the real R400 is paired with its receiver meaning that you can use two presenters at the same time. When you operate two of the fake presenters at once the receiver will react to both.

Other than the above mentioned difference they install as an ordinary HID device and will operate as a standard USB mouse with the generic Linux or Windows drivers.

The real deal will announce itself as a Logitech USB Receiver, the other will announce itself as a HAS HS304. Looking for that as an IC number I only found some Bluetooth headsets with a similar named chip, but no datasheets to be found. The chip inside the receiver stick has no markings either... Bastards!

Range? Range is ok, about 20 meters. The real R400 seems to be better in that regard though as I have seen those devices bridge 50 meters occasionally...

Other than that the back cover does not fit the original one. Bummer...