$25 Web Server-Start

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A $25 WEB SERVER

by Steve Freyder, David Helland, Bruce Lightner

Start • Network Adapter • Firmware Description • Software Development • Firmware Development Environment • The Next Generation And Beyond • Sources

A $25 WEB SERVER

The recipe is easy. Take an Atmel single-chip microprocessor, hook it up to an off-the-shelf PC network card, add a little code, and presto—you’ve got the web server shown in Photo 1. This circuit is so simple that you can build it in an evening and add worldwide web access to your favorite embedded application.

The PicoWeb server provides web access to digital I/O and serial I/O signals without the need for assistance from external PCs or Unix computers. It’s a stand-alone device with a real-time networking kernel, a TCP/IP stack, and an HTTP web server. Plug the device into an Ethernet cable connected to the Internet, and you can control your sprinklers from any place on the planet.

(click here for Photo 1)

Photo 1—Here’s the PicoWeb server breadboard with a $9 ISA-bus net-work card and an Atmel AT90S8515
8-bit microcontroller. Connectors at the bottom provide a serial port and an in-circuit programming port using a PC parallel port cable. Power (150 mW typical) is supplied by a +5-VDC wall wart.

This project started partly as an excuse to use a new microprocessor and partly to settle a long-standing argument about the possibility of delivering web pages with a commodity microcontroller. The Atmel AT90S8515 microprocessor looked exciting with its low-power RISC processor, 8 KB of flash program memory, 512 bytes of EEPROM, 512 bytes of RAM, 32 I/O lines, and a built-in UART. The realization that we could attach the Atmel part to an inexpensive PC ISA-bus network card with zero glue logic gave us a test vehicle to finally settle our argument (see Figure 1).

(Click here for Figure 1)

Figure 1—The PicoWeb server breadboard makes a simple "glueless" connection of an Atmel AT90S8515 microcontroller to a PC ISA-bus connector. Also included is a 24C128 16-KB serial EEPROM, diagnostic LED, manual reset switch, connectors for power, serial port, and the in-circuit programming cable. The inset shows the wiring diagram for a PC parallel-port programming cable.

With an execution rate of one instruction per clock and a clock rate of 8 MHz, the AT90S8515 can transfer data over the ISA bus at full speed (about 2 MBps). All the hardware we needed to make a web server was quickly put into place. For debugging purposes, we hooked up the micro’s serial port to a cable with an RS-232–level converter embedded in the DE-9 connector’s hood. We also added a single LED for feedback.

After all that, we still had a little bit of money left in our $25 budget, so we threw in a $2 16-KB serial EEPROM chip to hold things like GIF and JPEG images (web pages need pictures, don’t they?). With all the hardware together, it was just a matter of programming!

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