[Gta04-owner] GTA04 hardware suggestion and discussions
glenn.mh.dk at gmail.com
Sat Jan 22 23:34:50 CET 2011
Here are some hardware suggestion for discussion:
1) Possibility of IR RC5 receiver/transmitter
2) Possibility of IRDA transceiver
3) Possibility of a "video-link"? Use
touch-screen as a color matrix (2D) barcode video
transmitter - and the camera as a receiver (half
or full duplex). Let the link automatically adapt
to to half duplex, if you need to turn your
smartphone to establish the other half duplex
connection. The link should also adapt frame rate
and if the camera and/or screen is dirty - or the
link is through a dirty window. I have no idea
how fast the link can be as a function of
distance. The link should automatically adapt if
the video color matrix (2D) barcode is mirrored
in any way - or "played" backwards.
4) Antenna diversity of (preferably pattern,
space - or polarisation diversity):
* GSM/UMTS? (receive diversity incl. external antenna).
* 802.11(a)bg(n) (diversity) (W2CBW009Di: "For
Dual Antenna application") Almost every laptop
* FM-receiver (receive diversity requires
2*Si4721 - uC selects the best signal (listen to
one - let the other turn on and scan when the
listen-signal has to low S/N ratio) - or you can
listen to one and record another).
* GPS? (receive diversity including external antenna).
For FM-diversity you can use a 180 degree hybrid
(two loaded LC-circuits?) to separate common-mode
and differential-mode - for diversity - if three
space divided poles are available. I know that
there is a capacitance between ear-wires and
their ground, so I do not know, how well it will
work. Note that some impedance matching might be
For VHF/FM the head-phone cable might be used.
The diversity might be implemented isolating
ground by a adequate inductor (100MHz parallel
LC-circuit) - and two high-pass filter from left
and right earphone non-ground wires - and the
GTA04 itself as a kind of "ground"/third-wire.
Matrix (2D) barcodes:
An antenna that can be sized for 100MHz reception
around the perimeter of the PCB? Use two loops so
ground is not needed:
Also for 100MHz:
(T2FD -- The Forgotten Antenna:
1/3/2003 Antenna Diversity Strengthens Wireless LANs:
Quote: "...While detailed implementations of
dynamic diversity can vary widely, it's possible
to summarize the simulated performance of a
conceptually simple scheme relative to that of a
single-antenna mode, as well as full diversity
and selection diversity (Figure 6)..."
Spatial diversity employs multiple antennas,
usually with the same characteristics, that are
physically separated from one another. Depending
upon the expected incidence of the incoming
signal, sometimes a space on the order of a
wavelength is sufficient.
Pattern diversity consists of two or more
co-located antennas with different radiation
A polarisation difference of 90° will result in
an attenuation factor of up to 34dB in signal
strength. By pairing two complementary
polarizations, this scheme can immunize a system
from polarization mismatches that would otherwise
cause signal fade. Additionally, such diversity
has proven valuable at radio and mobile
communication base stations since it is less
susceptible to the near random orientations of
Diversity is only of value for the relatively
rapid fading caused by multipath. This kind of
fading is encountered extensively at HF and for
tropospheric and iono- spheric scatter
propagation at higher frequencies. Similarly,
mobile vehicles passing through a static
multipath field at VHF and UHF encounter such
fading as a result of their motion.
180 degree hybrid:
"Sum" uses sum of ear-wires - and third-wire.
"Difference" to some extent uses only ear-wires.
90 degree hybrid:
"X" uses ear-wires in one direction.
"Y" uses ear-wires in the other one direction.
180 degree hybrid and 90 degree hybrid might be
combined. One 90 and two 180 degrees? Then you
have 4 receive pattern diversity output ports.
Simultaneous Equalization and Rx Diversity on all
bands (Advance Receiver Type 3i), except for
Primary, diversity and GPS antenna contact pads
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