Servo - July 2010

provides the TCP/IP stack. In addition to these two devices, you will need to run some web code on a local machine. I happened to use another NetBurner device, but any web server (including your PC) can work for this.

Using a Web Server

It is possible to use the MOD5270 built-in web server. However, I did not go this route as it requires an expensive static IP address for your mobile connection. A static IP address has a few downfalls, as well. If your device does not currently have a mobile connection, then the web page would not exist, and the end user would get a 404 “website not found” error. With a local web server, the application can always state the last known position of your robot.

The web server interface uses the Google API to provide a familiar Google Maps’ style interface. Google has provided a great API for creating simple GPS applications. With the Google API, the application’s webpage is able to plot the robot’s location anywhere in the world with both satellite imagery and easy to read maps. If your bot is near

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a photographed street location, then it also provides a panoramic eye-level view of the area.

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Setting Up the Hardware

Hardware configuration is not too difficult. The biggest challenge is finding the 3.8V required by the Telit chip. In my setup, I had 5V and 3.3V power available. The schematic illustrates how I obtained 3.8V from the 5V source. The MOD5270 requires 3.3V. With 3.3V power already available, no voltage level translation is required.

The two devices require four lines for serial communication. Two of the lines will be reading the GPS values while the other line will be controlling the GPRS mobile connection.

Finally, you will need a way to toggle the Telit chip on and off. The on/off switch on the Telit device works exactly like a power button on a cell phone. It is a simple toggle that must be held for at least one second. Once held, the power will toggle either on or off. In the case of the Telit chip, you must pull the on/off switch down for at least one second to toggle the power.