Would you like a wireless web server that consumes almost no power and can be easily interfaced to other circuitry? The Webserver in a Box (WIB) project published in SILICON CHIP from November 2009 to January 2010 has been very popular but it lacks a WiFi interface. It’s also rather limited in regards to other capabilities; for example, the WIB has no support for DHCP (Dynamic Host Control Protocol) which allows for automatic IP address allocation.
Fig.1: this screen grab shows the menu item (circled at bottom left) that must be selected in the WR703N’s web interface to upload the OpenWRT firmware. It’s then just a matter of clicking the button to the right of the text input box to bring up the file “chooser” dialog.
If you hack a TP-LINK TL-WR703N router, you can overcome all these problems. It’s sold as a tiny “G Travel Router” but you can easily re-flash it to run a version of Linux. It’s then a relatively simple matter to set up a web server, an email server and so on. This is dramatically smaller and cheaper than a typical PC and it does all this while drawing about 1W of power!
Consider what this means; not only can you run a low-traffic website off this device, you can monitor temperatures, switch devices on and off and so on, without even needing a wired network connection. All you need is a source of low-voltage DC power and wireless internet access, plus the re-flashed WR703N.
The TL-WR703N is actually a fully functional miniature computer, shipped with software to make it operate as a 3G/WiFi router. This device is available from Hong Kong on eBay for only $25 delivered to Australia, making it a good choice for the home experimenter. Just go to the eBay website and type “WR703N” into the search box.
Making some mods
Fig.2: the next step is to select the OpenWRT firmware file that you downloaded in Step 3 and click the OK button. You then click the OK button again in the next dialog box to confirm the file selection and start the new firmware installation process.
What’s the catch? Because TP-LINK made this device for their domestic market, its default user interface is in Chinese. We’ll show how you can remove its built-in firmware by installing Linux over the top, without having to learn a new language. All you need are some basic computer skills and a general understanding of computer networking concepts.
Inside the WR703N’s tiny 57mm square plastic case is an Atheros chipset containing a MIPS-based CPU, 802.11b/g/n 150Mb wireless (WiFi), 4MB of flash storage and 32MB of RAM. As well as its USB2.0 and 100-base-T Ethernet ports, the only other port is a Type B micro-USB socket by which the device is powered (a suitable USB cable is supplied with the device).
Note, by the way, that the WR702N model is not suitable. It’s similar to the WR703N but only has 2MB of flash memory and 16MB RAM.
Nominally running off 5V, the WR703N’s average power consumption (with no USB device attached) is only 0.5W but it can draw more than double that when the CPU & Wifi are being used. Enthusiasts on the internet say it will work with an input voltage as low as 3.7V, meaning it can be run straight off a single Lithium-Ion cell. In fact, TP-LINK did this with the similar but more expensive TL-MR11U model, which comes with a built-in 2000mAh cell.