Teardown: Wireless keyboard and remote senses motion

-November 03, 2016

Last time, I disassembled the Mohu Channels, a Kickstarter-funded and now-discontinued network streaming device with an added twist: built-in ATSC reception support. In that prior writeup, I showcased (among other things) the primary unit's built-in proprietary 2.4 GHz RF transceiver (Beken Electronics' BK2433) and accompanying antenna, which I mentioned enabled it to pair to and communicate with the accompanying wireless remote control/keyboard (which I showed in the overview photo that opened the article, and I'm repeating below).

I also mentioned that the remote control/keyboard would be the focus of my follow-on (i.e. this) teardown. Before I dive in, however, I'll briefly mention something that I forgot to discuss last time. You may have noticed that I neglected to do a complete dissection of the Channels; I didn't, for example, take the heat sink off the Amlogic AML8726-MX application processor. That's because I have high (albeit potentially delusional) aspirations for Channels' ongoing use.

Last July, I mentioned that SiliconDust was in the process of developing a subscription-plus-OTA television reception-and-playback server-plus-client system called HDHomeRun DVR. The company's Kickstarter outreach exceeded expectations and, although the development pace has been slower than initial expectations, the product now supports non-protected content via Kodi, with full content support anticipated for later this year. Planned playback clients will include Android-based devices, such as the Nexus Players (along with USB-to-Ethernet adapters, as I've heard the units' integrated Wi-Fi is woefully inadequate) and NVIDIA Shield that I've stocked up in anticipation of trying the product out for myself (my server options include a spare Windows 7-based headless PC and a WD My Cloud NAS that I acquired especially for this project).

Well, the Mohu Channels is also Android-based, and better yet, it includes built-in wired Ethernet. Is its final Android version (never to be further upgraded, at least by the company) supported by the HDHomeRun DVR client application? Does it support Android's optional (and hardware-dependent) content protection scheme, necessary for television service providers like Comcast? And does it implement hardware-accelerated graphics and video support, necessary to make HDHomeRun DVR playback an acceptable experience? All are TBDs at this point, but I didn't want to prematurely sacrifice a potential viewing platform.

Enough of the Channels base unit discussion: on to the keyboard. To begin, here are a few closeups (it's 2 ½ × 5 ½"):

Slip off the dual-AAA battery cover, and the "Learn" and "Pair" buttons (with an LED in-between them) come into view. Their functions are described here:

The top and bottom halves of the enclosure are held together by glue-augmented plastic tabs. The adroit application of a svelte screwdriver enables prying them apart. Here's the back-side of the top half:

And here are front and back views of the rubberized keyboard below it:

Keyboard button depresses activate switches located underneath each of them:

In the upper left corner, you'll find the LED used for keyboard-illumination purposes:

And in the upper right corner you'll find the photodiode that assesses the ambient-light need for this supplemental (and battery sapping) LED enhancement:

Pull the PCB out of the enclosure, flip it over, and here's what you'll see:

Click to enlarge.

Your first thought might be one of confusion. Didn't I earlier say that communication between the keyboard and base unit was RF-based? I did. Then why is there a large IR transmission LED at the top-and-center of the PCB? That's because the Channels' keyboard can also optionally remote-control your TV. Also, here's a close-up of the earlier-mentioned two-switch-and-LED cluster for "Learn" and "Pair" purposes:

Click to enlarge.

Most of the action, however, takes place in the upper right corner of the PCB. Here's a partial zoom-in on it:

Click to enlarge.

In the upper left corner is the aforementioned IR LED. To its right, in the upper edge, you can see the thick trace representing the embedded 2.4 GHz antenna. And below it is another BK2433 2.4 GHz transceiver from Beken Electronics; this one a larger-packaged, higher-pincount sibling of the one found in the base unit.

Remember, too, that the Channels' remote control supplements keyboard-based functions with motion-activated on-screen cursor facilities, acting as a sort of wireless (and pad-less) mouse in the process. As the FAQ notes:

The device translates the speed at which you move the remote into cursor movement, not distance traveled. If you move the remote faster the cursor will move a greater distance.

Clearly, there's a three-axis gyro somewhere. Zoom in further, along with rotating the PCB 180 degrees, and it'll come into clearer view. It's the ITG-3205 from InvenSense:

Click to enlarge.

This concludes, at least for now, my coverage of the Mohu Channels system. If and when I get it working with SiliconDust's HDHomeRun DVR setup, I'll let you know via a follow-on post. Until then, I welcome your comments, as always.

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