Tuesday, 2 October 2012

RaspberryPi Access Point

This is the RaspberryPi (RPi) running as an access point (AP).  Okay doesn't look like much, but this is pretty advanced stuff, yet as always relatively simple in Linux once you know what to do.  The key is the D-Link DW-140 wi-fi dongle perched on top of the RPi, which can act as an access point.  Not all wi-fi dongles can do this, but loading the 'iw' wi-fi tools package in Linux and running 'iw list' outputs diagnostics which will tell you if a connected dongle can run in AP mode.

All the details are helpfully on this guy's blog -


Now my motivation for looking into this was the desire to use one of the tablets as a front end for a vehicle diagnostics system.

Problems -

  • Cheap Android tablet computers don't have serial or Bluetooth capabilities;
  • Without Bluetooth or serial how do you communicate;
  • While these can be added, it is complex as the Android ROM has to be altered;
  • They do have wi-fi as standard, but Android doesn't like ad-hoc networks, only access points;

So the RPi acts as a proper AP, not an ad-hoc network, complete with DHCP for managing IP addresses automatically and it can run an Apache server, PHP, MySQL and anything else you fancy.

And here it is.  The IP address is, which is the address of the RPi running Apache as the server for this test.  There is no link to the Internet so this is really a point-to-point set-up between the RPi and the tablet.

The next step is to log some data over the RPi's USB-Serial connection and somehow get this served out to the tablet.  I'm thinking of an AJAX solution (although a Java Applet is also tempting if I knew Java), with the data formatted into an XML file maybe using Python so I have an excuse to learn some Python.  That might allow regular (say 1 per second) updating of the data into a live graph and I have been experiementing with simple bar charts using JavaScript this summer past.

Now I need to find out more about AJAX.

1 comment:

  1. I am faced with a similar issue.

    The problem I face is more of a kisok showing a chromium browser as more of a advertisement platform.

    Would you be able to upload a image with of your setup hostapd, apache/mysql/php all setup/installed.