Sunday, December 28, 2014

Wireless TV transmitter / receiver - teardown and repair

I've recently bought a broken wireless video RX/TX pair off of eBay. The audio was being received properly but there was no video.

Since the system works at 5GHz there is no way to easily figure out if it's transmitter or receiver at fault.




In the end I managed to get it working and took some pictures in the process.

EZCast M2 teardown

The microUSB plug on my newly acquired EZCast / Miracast dongle came loose so, obviously, I had to take it appart.

The system is based around a single chip: AM8251 - a single-core ARM9 system-on-chip built specifically for this purpose.
There's an XDA thread on units similar to this:
http://forum.xda-developers.com/showthread.php?t=2632288
and on one of the manufacturers' forums:
http://forum.iezvu.com/bbs-en/viewtopic.php?f=2&t=802

The big chip on the other side is a Samsung NAND flash chip, probably this one (K9F1G08U0E).
I don't know what the smaller IC is, but I assume it's the WiFi stack chip.

Small review:

It does the job fine especially at 720p. Ironically (or not) AirPlay mirroring has less lag and dropouts than Android mirroring. Tested with iPad Air, Galaxy S5 and Motorola Razr.

Other users are complaining about a lot of dropouts but I'm not experiencing that. I'm sharing the WiFi through a FritzBox 7390, so perhaps the quality of the router also matters.

Unfortunately it cannot fully replace the existing ChromeCast dongle I have so I'm forced to use both: ChromeCast for YouTube videos and EZCast for everything else.

Desktop mirroring is decent, I can stream Amazon Prime ('Instant Video') movies and they are watchable at 720p. At 1080p the framerate is too low. Tested with a Core i7 laptop running Win8.1 through a 300Mbps wireless connection on 5 GHz.





Central ventilation augmentation

My apartment building has a central ventilation system built-in. While it does a pretty good job at getting the kitchen smells out it also makes a lot of noise and wastes heat when closed.

Out of the many possible solutions I decided on building a cover that goes on top and is activated by the red LED that lights up when the original ventilation system is turned on. This means no messing around with mains - galvanic isolation.

After the break, the story of going from this:


to this:

Along the way there will be some interesting tidbits - original design, capacitive light sensing, low-power techniques and code.