Naked hardware #12: USB Audio Transmitter

USB Audio Transmitter teardown

This time I decided to teardown a little bit different hardware as usually - radio transmitter.

unbranded USB Audio Transmitter

USB Audio Transmitter

Key components:

Holtek HT82A821R
Quintic QN8027

General info

It is cheap noname USB audio transmitter, that is supported beginning from the Linux Kernel 3.4. Kernel driver name is radio-keene, done by Norwegian V4L superman Hans Verkuil.

Device has a USB ID 046d:0a0e assigned. That ID seems to belong Logitech, but likely company has nothing to do with device itself. Maybe the ID is just chosen because Logitech uses it on some USB speakers?

Device starts transmitting just after it is plugged on 95.160 MHz. Use of device is very easy as it implements itself as USB speaker - just plug it to the USB port and select proper audio output from volume control. There is some extra controls available via V4L2 interface, like a frequency setting and TX power. Check and tune using v4l2-ctl tool, "v4l2-ctl -d /dev/radio0 --all" lists all settings.

Hardware internals

PCB top side

All components are assembled to that side of the PCB. Bigger chip is HT82A821R and smaller is QN8027.

HT82A821R is USB speaker chip that supports standard USB audio profile.  The other chip, QN8027, is of course FM transmitter. Two similar looking metal tubes are clock sources. Unfortunately I forget to check clock frequencies, but according to datasheets HT82A821R supports 6 & 12 MHz and QN8027 supports 12 & 24 MHz.

Black wire is antenna, which is physically connected to the metal side frame giving physically a little bit more length.

PCB bottom side is almost empty

PCB bottom side

No components on that side, but still something. There seems to be about half of the antenna wired directly to the PCB.

BL-UAT82 V 1.0 ?

USB interface

IDLE current drain without a driver: 38mA



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