The “BOOT” button connects to the MG2639’s PWRKEY input, which turns
the module on or off. This button works exactly as you might expect any cell
phone power button to work. If the module is off,
hold the button down for
2-5 seconds
then release to turn it on. If the module is on and you hold the
button down and release, it’ll turn off.
Control of this button is shared between the physical button itself and
Arduino pin 7. The Arduino pulling pin 7 LOW has the same effect as
pushing the button down. This gives the Arduino machine control over the
module’s ON/OFF status.
Bottom-Side Jumpers
To keep the Shield as multi-purpose as possible, there are a number of
jumpers on the backside that can be used to switch the interface pins or
power supply.
To open any of these jumpers, use a hobby knife, and remove the small
trace between any two connected pads. To connect a jumper, solder a
small solder joint between two pads.
Here’s a quick rundown of each jumper:
•
VDDIO
– This jumper selects the voltage for logic running into the
high side of the shield’s TXB0104 level shifter. It defaults to 5V but
can be switched to 3.3V if your application requires.
•
Cellular UART RX and TX
– These jumpers allow you to switch the
cellular module’s RX and TX between either pins 2 and 3 or 0 and 1.
That means selecting between a software (2/3) or hardware (0/1)
UART.
•
GPS_TX and GPS_RX
– Like the other UART jumpers, these allow
you to set the GPS module’s UART to either software (8/9) or
hardware (1/0).
•
VGPS Disable (SJ4)
– This jumper controls power delivery to the
shield’s GPS module. If you don’t want to use the MG2639’s GPS
module, and want to avoid the power loss it incurs, cut this jumper.
•
VBAT Enable/Disable (SJ2 and SJ3)
– If you want to power the
Cellular Shield from a single-cell lithium polymer battery, you’ll need
to attack both of these jumpers. Shorting SJ3 will connect the JST-
footprint connector directly to the module’s power supply. Opening
SJ2 will disconnect the voltage regulator output from the rest of the
circuit.
•
FTDI Power Enable (SJ8)
– If you want to use an FTDI Basic to
troubleshoot the MG2639’s UART, this jumper will allow you to power
the VDDIO line with the FTDI’s VCC pin.
•
BOOT Control
– This jumper allows you to remove Arduino pin 7
(mislabeled “6” near the jumper) from the MG2639’s boot button.
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