The Vodafone K3770 Dongle allows you to connect your mbed to the internet from (almost) any location in the world.

The K3770 dongle can be purchased directly from Vodafone, or is available in most Tesco Stores that have an "In-store Phone Shop".

Hardware¶

You can use a female USB A connector to interface the dongle. Wire up the dongle's power and ground lines to a good +5V source and to the mbed's ground, respectively. Connect the mbed's D+/D- pins to the USB plug.

Here is how to connect the dongle to the mbed's USB host interface.

Power¶

The dongle should have a reliable +5V power source. While establishing connection, and low coverage areas, the dongle can draw as much as a few hundred mAs. To avoid any problems with supply, it's recommended to use an external power supply as opposed to a single USB port shared with the mbed. Additionally putting a couple capacitors between the dongle's power line and the ground (0.1µF, 100µF, 10µF) can help smooth the spikes and compensate for current surges.

Data¶

To use the mbed in USB host mode you need to add two 15K pull-down resistors on the D+ and D- lines, as shown in the schematic.

Additional Hardware Used¶

The below components were also used to build this prototype.

• USB A Socket
• Breadboard Power Supply
• Breadboard
• Jumper Wires

Software¶

Library¶

You need to import the VodafoneK3770Lib library, include the relevant header file and instantiate the VodafoneK3770 object.

On your first call to any of the library's function, the dongle is initialized.

• The USB interface is configured and the dongle is detected
• The dongle is switched to modem mode if needed
• The dongle registers to the network (can take up to a minute)
• If needed, the dongle is configured for the network it has reached

Examples¶

Mobile Internet¶

You can connect to the internet by establishing a PPP connection. You can then use BSD Sockets or any high-level component (HTTP Client, NTP Client).

To connect, one single function is used:

int ret = threeg.connect("pp.vodafone.co.uk");

pp.vodafone.co.uk is the APN value for a Vodafone Pay as you Go SIM. Change it to the relevant value if your SIM is different:

For details please check Vodafone's dedicated page.

The variable, "ret", allows you to check whether the connection was successful or not (0 on success, a negative value on error).

Please note that this command can take up to a few minutes to complete in worst case scenarios - it actually initializes the dongle and waits for network registration, which can take quite a long time.

Once connected, you can use any high-level component:

• HTTP Client
• NTP Client
• Websockets

You can also use the BSD Sockets API directly.

Here is a full example program for fetching a web page using HTTP.

Sending and receiving SMS¶

The library offers simple functions to send and receive text messages. Please note that you cannot use these functions while connected to the internet.

Network Time Protocol¶

Use the dongle to set-up your mbed's Real Time Clock:

Websockets¶

WebSockets are also supported:

Balance Check¶

This example uses USSD (Unstructured Supplementary Service Data), and will return your remaining balance (if you are using Pay as you Go).