With a long term goal of being able to add the ability to send/receive SMS text messages, over cellular telecommunications, to/from an Arduino-type remote device, I read the blog of New Zealander Brody Radford with interest. His blog explains the simple modification to a $25 cellular data USB modem that permits easy operation on any operating system. The $25 cellular data USB modem is sold by the reliable Chinese company DealExtreme under the name “USB Tri-band GPRS Modem / Cell Phone Radio (GSM 900/1800/1900Mhz)“. As delivered, the modem will only work on Windows and only with their driver supplied on an included CD. However, using Brody Radford’s directions, unsolder and lift up one IC pin and the modem will work perfectly on any operating system. With Windows you’ll need to load the Prolific drivers, but Linux is just Plug-and-Play as a USB serial device – no drivers needed. Brody also explains how to further prepare the modem for connection to a microcontroller by unsoldering two more pins (TX and RX) for direct connection, by new wires, to a microcontroller/Arduino.
I particularly like the first step of Brody’s instructions “1. Toss out the supplied user guide and CD.”
I have tested the modem to send/receive SMS messages to/from my Verizon cellular telephone. I equipped the DealExtreme GPRS modem with a T-Mobile pre-paid SIM card, which works perfectly. Each SMS message costs ten cents, with no other costs.
Here is some sample serial output:
Aug 8 09:01:29 pennyroyal kernel: [1012914.220113] usb 5-2: new full speed USB device using ohci_hcd and address 3
Aug 8 09:01:29 pennyroyal kernel: [1012914.405387] usb 5-2: configuration #1 chosen from 1 choice
Aug 8 09:01:29 pennyroyal kernel: [1012914.407228] pl2303 5-2:1.0: pl2303 converter detected
Aug 8 09:01:29 pennyroyal kernel: [1012914.429273] usb 5-2: pl2303 converter now attached to ttyUSB0
SW ver: 1.80
HW ver: 1.00
FS ver: 1.00
Build Date: 2004/6/25
Build Time: 18:40:37