3Cell UART

RX

Cell module's data receive (4800 baud).

7

Cell boot

pin

This pin has the same control over the module

as the BOOT button (explained below).

8

GPS UART

TX

GPS module's data output (115200 baud).

9

GPS UART

RX

GPS module's data receive.

Cell and GPS UARTs

Communication with the cellular and GPS module’s occurs on two separate

serial UARTs. To leave the Arduino’s hardware UART free for debugging

and uploading sketches, both UARTs are broken out to digital pins –

intended for use with the SoftwareSerial library.

Because the SoftwareSerial library can’t reliably support high-ish baud

rates, we’ve intentionally slowed down the MG2639’s cellular UART to 4800

bps, rather than the module’s default bit rate of 115200. This slower rate

ensure data reliability, and gives the Arduino some extra time to process

large strings.

The GPS UART is hard-coded to 115200 baud, which make it harder to

use with SoftwareSerial. Instead, we recommend using the AltSoftSerial

library with this part of the module.

Either of the two UARTS (the cell or GPS) can be switched over to the

Arduino’s hardware UART. Check out the “Jumpers” section below for more

information.

LED Status Indicators

There are a trio of LEDs on the MG2639 Cellular Shield which indicate

connectivity or power status:

• POWER – This red LED is connected to the MG2639 module’s

power supply line. If this LED is on, the module is receiving power.

• RSSI – This green LED indicates the status of your cellular network.

It’ll blink at various rates to show what state it’s in:

◦ OFF – The module is powering on (assuming it has power).

◦ 1 Hz blink – Module is idle.

◦ 3 Hz blink – Searching for a network.

◦ 5 Hz blink – Module is in a traffic state (a phone call or data

transmission).

• GPS – GPS fix indicator. This yellow LED will illuminate when the

MG2639’s GPS module gets a solid fix.

Boot & Reset Buttons

Two buttons labeled “BOOT” and “RESET” are built into the shield. The

“RESET” button is simply the Arduino reset, it’ll have no direct effect on the

MG2639.

Page 4 of 22