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USER MANUAL FOR HARDWARE REV 3.11
07-APR-2018
PAGE 9
3.6
GPS OPTION
An expansion header is provided so you may add an off-the shelf GPS
board (
SparkFun.com #GPS-11058
). The use of this GPS unit also
requires the purchase of
qty 2, PN ED5908-ND from Digikey
, and the
GPS antenna of your choice with SMA interface. We have tested
Sparkfun #GPS-00464
, but any passive GPS antenna should work fine.
Installation of the GPS antenna requires the connectors be soldered
on the
BOTTOM
of the GPS board as indicated by the silk screen.
We suggest installing the pins first into the repeater board sockets,
mounting the GPS board to the pins and then soldering to ensure
proper alignment as the female sockets float a bit in the holes and
may also be slightly angled.
NOTE: using the GPS board is very close to the LCD flex cable socket,
and may interfere with the ability to use a touch screen depending on the cable used. We have
successfully folded back a ribbon cable while having the GPS unit installed, but the clearances are tight
and the tight bend radius may damage your flex cable, have a spare flex cable and proceed with
caution.
NOTE: “UART/GPS” switch must be in the correct position as shown for the
GPS to communicate with the Raspberry Pi platform.
3.7
I2C EXPANSION
A 4 pin header has been included to allow you to expand the I2C bus to include
your own devices, but you must ensure that the signals are 3.3V. Voltages
above 3.3V will damage both the Raspberry Pi and the repeater board. Zener
Diodes are included in the data signals, but should not be counted upon to
protect the boards from overvoltage.
It is recommended to utilize MCP23017 gpio expander device if additional gpio functionality is desired.
The MCP23017 device is recommended due to wide usage and support provided by current raspbian
distributions.
Note:
Use of this chipset requires a user developed Device Tree Overlay to prevent
interference with the PTT and existing GPIO expander functionality. The provided overlays only
support the chipset already on-board, which is part of the repeater board’s core functionality.