A friend recently bought me a TP-Link WR703N in China for just 98RMB (that is 15$ or 12 €)!!! It is really an incredible piece of hardware including a 400MHz ARM (Atheros AR7240), Ethernet connector, 802.11 b/g/n wlan, USB port, 4MB flash and 32MB RAM. You even get a power adaptor and the device consumes just 0.5W. When it runs Linux (OpenWRT) I personally think that it is as or even more attractive than the 25$ raspberry PI. The only thing missing is access to the on board serial interface which I wanted to solve. Instead of adding a new connector to the case I simply used two of the available lines in the micro USB connector (used as the power connector for the router). This means that I can access Tx and Rx, GND and 5V thru the included USB cable. On the router there are two small copper colored test pads next to the ram (on the opposite side of the Ethernet connector). They are labeled TP_IN and TP_OUT. I connected the wires to the decoupling caps C55 and C57 next to the pads, since they were already tinned.
I have already started to build a small PCB with a microprocessor, a mini USB connector for power (using the routers power adaptor with a standard USB mini cable) and a USB typeA female that provides power and serial connection to the router. The board has a lot of available I/O, an IR receiver and debug led’s. This board can be used to connect almost anything to the web. I think I will start with a 433MHz radio interface to control the lights at home.