The Buffalo AirStation Wireless-G (WHR-G54S) router is one of those off the shelf products that is absolutely a hacker's delight. Officially, the device is intended for use as a home router to sit between your cable modem and your various computers around the house, wireless and wired. Unofficially, however, the device is an embedded Linux platform that you can program to do anything you want.

At the time of this writing, you can buy a WHR-G54S for a mere $25 (after rebates) from Circuit City. Even without rebates, the device is still a steal at $40 to $50 elsewhere.

Specifications

• 200MHz Broadcom 5352 Network Processor (32-bit MIPS instruction set).
• 4MB FLASH, 16MB RAM
• Small 3.3V 2A floor brick power supply
• 802.11g wireless (supports access point and client modes)
• 4 port 10/100Mbps Ethernet switch, plus 1 additional Ethernet port.
• Custom Linux firmware can be FLASH programmed via TFTP on power up. Probably very little chance of irreversibly bricking the unit.
• Internally has solder holes for connecting one serial port (RX/TX pins only)

Serial Port

Internally, the circuit board has unpopulated solder holes for connecting a 3.3V TTL serial port (no hardware handshaking signals though, just RX/TX). This opens the possibility of using this device with your microcontroller projects, providing wireless network access and remote control. Most wireless serial device servers cost upwards of several hundred dollars and provide far less functionality.

If you want to interface to RS-232 voltage levels (such as those used on a PC serial port), you'll need to use a MAX3232 chip. I've put together a quick little schematic diagram showing how to do it.

Firmware

Pre-built custom firmware packages:

DD-WRT - Very feature rich router firmware. Great if you just want to use the device as a router without writing any custom firmware yourself.
OpenWrt - Less features, more geared towards customizing the device yourself. Good SDK package.
Tomato - Yet another router firmware package.

Personally, I would like to see someone integrate the RFC2217 protocol into the device so that we can use the serial port over the network. There is already an open source implementation of this protocol available for Linux, but so far I haven't seen it integrated into the above wireless router firmware packages yet:

sredird - RFC 2217 compliant serial port redirector (runs under inetd service)