Tag Archives: Streaming Radio

Building a Wifi Radio – Part 3, Hacking the Asus WL-520GU

This is the third part of an ongoing series about building a low cost, open source streaming internet radio.  If you haven’t already, check out part one and part two for some background about the project.

Hacking the Asus WL-520GU Wireless Router:

In the last part of this series, I selected the Asus WL-520GU wireless router as a suitable embedded platform for my Wifi Radio project.  I have since posted some detailed specs on this impressive low-cost router, revealing it’s powerful Broadcom BCM5354 core, 4MB flash, and 16MB SRAM.  Granted, there are many more powerful routers out there that have USB support, will run Linux in various forms, and have built-in WiFi.  However, the WL-520GU does almost everything we need to build a streaming internet radio and costs under $50 (I have seen them for as little as $26 after rebate), which is very impressive indeed.

To convert this router into a powerful embedded system, we need to make a couple modifications.  First, we need to throw out the stock firmware. It turns out that this router, like many others, runs Linux from the factory.  However, because it was designed to be a wireless router and not much else, the stock firmware doesn’t include a very wide set of features (and certainly was not intended to be accessed by the customer).  Thankfully, there are several open source Linux distributions available that support this router, including my favorite, OpenWrt.  In addition, Asus has made it fairly straightforward replace the stock firmware with our own custom Linux build which can include all the programs, drivers, and utilities we can cram into 4MB of flash.


Before we start hacking the router, there are a couple things I should mention:

  • From this point onward, your warranty is toast. Don’t even THINK about trying to send a modified router back to Asus for warranty service.  In the end it hurts people like us, because Asus will try to make it harder for people to perform the same modifications in future products.
  • You may inadvertently destroy your router. If you are not comfortable with the fact that a misstep during the reflash or a stray solder bridge could ruin your hardware, stop now.  Sorry.  If you really take a wrong turn, you could damage your PC as well, but this is extremely unlikely.  If you do somehow damage your router or PC doing these modifications, I assume no responsibility for any damages!

This tutorial assumes that you have already established the router is basically working by assembling it, plugging it in and checking for it’s wireless signal and internal webserver.  The user manual does a good job of leading you through this process, but don’t use the supplied CD – follow the advanced/manual instructions instead.

Accessing the internal serial port:

The OpenWrt install will be easier if we can find a way to access the internal serial port of the router.  The built-in serial port gives us a way to view Linux boot and status messages and get shell access as well.  The serial port will also come in handy later when we want to add a user interface to the radio.

You will need:

  • A desktop or laptop computer with an open USB and Ethernet port.
  • Your shiny new ASUS WL-520GU wireless router (R1.02)
  • A strip of breakaway 0.1″ male header
  • A FTDI-232-3V3 USB to serial adapter cable ($20 @ Adafruit) or some other means of connecting a 3.3V level serial port to your PC
  • A small scrap of perfboard and a strip of female 0.1″ header (not strictly necessary, see below)


  • A basic electronics workbench with ample light, a temperature controlled soldering iron, a solder sucker, solderbraid, wirecutters, and pliers.  Servo Magazine recently held a contest to see who could build the best electronics workbench for under $100, the results should be helpful for anyone just starting out.  If you’re uncomfortable soldering, find someone else to help you with this part at your local hackerspace.

Step 1 – Open the router

Remove the power cord and antenna (the base unscrews).  Flip the router over and look at the bottom.  You should see something like this:

Asus WL-520GU

Note there are four screws that hold the router together, two are hidden underneath the rubber feet.  The feet are stuck on really well, but persistent prying with a fingernail will get them off eventually.  Remove the four screws and set them aside.  The top cover should come off without too much trouble.

Now that the router is open, you should see something like this:

Asus WL-520GU Wireless Router

Step 2 – Add a serial port header

Remove the PCB from the plastic enclosure by gently pulling it up and towards you (ethernet ports facing away).

Just to the left of the ASUS logo in the photo below, you will see a 4-pin header that I have installed to access the internal serial port of the router, the router ships without this header.  Instead, you will see four solder filled vias in a row in the same spot.

You will need to use your soldering iron and a solder sucker to remove most of the solder so that the header can be installed.  A higher power soldering iron will help with removing solder from the first via on the left (mine is a 60W Weller WTCPT).  This via connects to a ground plane which sucks heat away from the iron and makes the job more difficult.  Be patient and persistent and you should be able to wick any remaining solder away with some soldering braid if necessary.

Break a 4-pin chunk of male header off the strip.  Pop the header into the board and carefully solder it into place.  If it doesn’t fit, chances are there is still some solder left in the vias.  You should end up with something like this:

WL-520GU serial port

The pin functions are, from left to right in the photo:

GND   TX   RX   3.3V

Step 3 – Connect your PC

The FTDI-232-3V3 USB to serial adapter cable provides a handy way to add a 3.3V TTL level serial port to a PC or laptop.  The cable has a flat connector on the serial end that can plug directly onto 0.1″ male headers like the one we are using on the router.  Unfortunately, the pinout of the FTDI cable (given in the datasheet) does not match that of the router.  To resolve this, you have two options:

  • Use a tiny screwdriver to pull out the pins from the housing at the cable and rearrange them.  Do not connect anything to the 3.3V pin on the router, and swap the TX/RX so that the TX on the router feeds RX on the cable, and vice-versa.  Don’t forget to connect the grounds!  The downside of this is that now you can’t use the FTDI cable for things like the Boarduino without swapping the pins back.


  • Fabricate an adapter board using a small piece of perfboard and some headers, shown below (click for a larger version):

Asus wireless router serial port adapter Asus wireless router serial port adapter

Here is a schematic of the adapter board:

Shown here are the cable and adapter installed on the router.  Make sure the ground side of the cable is connected to the pin on the header that is opposite from the fat angled trace (the 3.3V line).  Ground is the black wire, on my adapter I marked this with a black dot so I won’t forget and plug it in backwards.

WL-520GU with serial cable installed

Step 4 – Test the connection

Plug the cable into your PC (you may need some drivers) and open your favorite terminal program.  (I like Zterm for the Mac or Hyperterminal on the PC.)   Using the terminal program, open the serial port corresponding to the FTDI cable (something like usbserial-FTDQ23LB on the Mac or COM3 on the PC, but your setup may be different.)   Set the port options to 115200 baud, 8N1.

Connect the antenna and power supply to the router and plug it in.  You should see something like this appear in your terminal program:

CFE version 1.0.37 for BCM947XX (32bit,SP,LE)
Build Date: Thu Mar  6 10:05:04 CST 2008 (root@localhost.localdomain)
Copyright (C) 2000,2001,2002,2003 Broadcom Corporation.
Initializing Arena
Initializing Devices.
Boot partition size = 131072(0x20000)
et0: Broadcom BCM47xx 10/100 Mbps Ethernet Controller
Total memory: 16384 KBytes
CPU type 0x29029: 240MHz

If you do, congratulations, your serial port is working!

The lines that scroll by are boot messages from the Linux kernel of the stock firmware on the router.  These messages give you a lot of information about the hardware in addition to information about the operating system and software drivers.  Here is a complete transcript of the boot log from my router.  If you wait a couple minutes for the router to finish booting and hit enter, you should see a command prompt.  From here you can explore and play around with the stock firmware, there is really not much to do here until we reflash the router with OpenWrt.

That’s it for part three.  In part four, I’ll talk about installing OpenWrt and connecting the router to your wireless network.

Update: Part four is now available.

Update 2: There is a new Wifi Radio Discussion Forum, hop over there to ask questions about the project or see what other people are working on!  (4/12/09)

Inside the SYBA SD-CM-UAUD USB Stereo Audio Adapter

SYBA SD-CM-UAUD USB Stereo Audio Adapter

I am using this tiny USB-audio adapter as part of my Wifi Radio project.  It’s a ridiculously cheap $8 at Newegg.com and contains a C-Media CM119 chip targeted at VoIP applications.  I have no idea why they chose to use a VoIP chip for this application because it contains a lot of bells and whistles that are not being used in this device, such as support for a matrix keypad!

SYBA SD-CM-UAUD USB Stereo Audio Adapter

Unfortunately, I have not been able to locate a datasheet for the CM119 so for now I will be using it only for it’s intended application – adding an audio output to a wireless router with USB.  Come to think of it, that is probably not it’s intended application, but it’s close enough.  Hooray for embedded Linux!

SYBA SD-CM-UAUD USB Stereo Audio Adapter

Building a Wifi Radio – Part 2, Choosing an Embedded Platform

This is the second part of an ongoing series about building a low cost, open source streaming internet radio.  if you haven’t already, check out part one for some background about the project.


In part one, I discussed the merits of streaming internet radio and the motivations for my Wifi Radio project.  Now it’s time to start looking at what hardware can make this project a reality.  Before we get started, let’s review the requirements list from last time.


  • Wireless connectivity through existing Wifi network
  • Audio output (preferably 44kHz, 16 bit stereo)
  • An integrated amplifier and speaker(s)
  • Shoutcast/MP3 streaming audio decode
  • Several builtin station presets
  • A display to indicate the station and currently playing song
  • Simple user interface, using standard radio controls (volume, tune, etc)
  • 110VAC operation

There are two additional requirements that I implied in the first post but forgot to include explicitly:

  • Cheap, priced below a commercial streaming radio – target < $100.
  • Small size so it can be portable (no desktop PC’s allowed!)

Selecting the hardware:

How do these requirements translate into hardware?  Let’s take a stab at what features we’d like in an embedded platform.

  • A wireless interface
  • Audio output
  • Sufficient system resources (CPU, memory, etc.) to decode MP3s
  • Some extra IO for a control panel and display
  • Low cost
  • Small size
  • Ease of development

The size and cost aspects pushed me towards an embedded system instead of a small form factor PC like any of Shuttle’s XPC offerings or a nano-ITX board.  To me, “Ease of development” equals Linux, so I wanted something well supported by Linux and an active open source development community.

There are quite a few embedded Linux platforms out there, with a wide variety of prices and features.  I looked at a few of them, including:

  • The Tin Can Tools Hammer – very impressive ARM9-based board with USB, lots of RAM and flash, lots of IO, and best of all the footprint of a 40-pin DIP package (breadboard compatible!).  No wireless and relatively steep pricetag ($160).

  • TI‘s Beagle Board – Incredible featureset including DVI output and a 600MHz ARM Cortex core.  No wireless and price is stunning for what you get, but overkill for this project ($150).  (Must keep in mind for future projects!)

    ASUS WL-520gU Wireless Router

  • Consumer wireless routers like the Asus WL-500gP v2 and WL-520GU – builtin wireless (yay!), USB, 240MHz Broadcom 5354 core, decent RAM and flash, cheap. Newegg has the WL-520GU for an incredible $26 after rebate (normally $50). The higher end WL-500g has more memory and flash and an integrated USB 2.0 hub (2 external ports).  Newegg has the WL-500g Premium V2 for $50 after rebate (normally $80). Both versions are a steal for what you get.

Tiny, under $50 and with built-in wireless, the Asus WL-520GU is the clear winner for this project.  The downside?  Since this router was never intended to do anything other than, well, route, we’re going to have to crack it open, modify it, and void the warranty.  In addition, there is no tech support and we’re going to have to spend some extra time hacking around to get it to do what we want.

Here it is in all it’s glory:

Asus WL-520GU Wireless Router Asus WL-520GU Wireless Router

Here’s a sneak peak of the inside:

Asus WL-520GU Wireless RouterAsus WL-520GU Wireless Router

This router is supported by OpenWRT, an open source Linux distribution for small embedded devices.  Ignore the work-in-progress designation, it works, trust me!

Although the router lacks builtin audio, that is easily solved with an $8 SYBA SD-CM-UAUD USB Stereo Audio Adapter. There have been reports that the WL-520GU only supports USB 1.1 reliably, but USB audio doesn’t require USB 2.0 so it’s not an issue for us.  For full USB 2.0 support, look at the WL-500gP v2 instead.

So far we have $58 into the project ($38 if you are lucky enough to get the rebate) and we have an embedded Linux computer, a wireless interface, and an audio output.  Not bad!

That’s it for part two!  In part three I’ll install a serial port on the router and get ready to reflash the stock firmware with OpenWrt.  At that point we’ll be able to start listening to some tunes!

Update: I posted detailed specs for the WL-520GU and a couple more photos here.

Update 2: I posted some images of the $8 USB-Audio Adapter I am using as well.

Update 3: Part three is now available.

Update 4: There is a new Wifi Radio Discussion Forum, hop over there to ask questions about the project or see what other people are working on!  (4/12/09)

Building a Wifi Radio – Part 1, Introduction

This article is the first of a series that will document the development of a low cost, open source wireless streaming internet radio receiver.  All construction details, including schematics, source code, and even the design process itself will be documented on this blog.

Comments and (constructive) criticism are welcome. Click here to post a comment.

Table of Contents:

  1. Building a Wifi Radio – Part 1, Introduction (you are here)
  2. Building a Wifi Radio – Part 2, Choosing an Embedded Platform
  3. Building a Wifi Radio – Part 3, Hacking the Asus WL-520GU
  4. Building a Wifi Radio – Part 4, Installing OpenWrt
  5. Building a Wifi Radio – Part 5, Let’s Make Some Noise!
  6. Building a Wifi Radio – Part 6, A Conversation with Mpd
  7. Building a Wifi Radio – Part 7, Building an LCD Display
  8. Building a Wifi Radio – Part 8, Adding a Tuning Control
  9. Building a Wifi Radio – Part 9, A Few Odds and Ends
  10. Building a Wifi Radio – Part 10, Building the Box

Some background:

According to Wikipedia, in 1993 the first internet radio program began distribution.  At that time, radio programs were manually downloaded to be played later on the user’s home computer; the user experience was far from that of listening to a traditional broadcast radio receiver.  It was not until several years later that streaming radio became common, giving birth to internet radio stations that could be listened to much like traditional radio, but with several advantages.  Most notably, internet radio stations were (and still are for the most part) largely devoid of on-air advertising, and stations anywhere on the globe could be received by anyone with access to the internet.  Over time, improvements in audio compression (such as MP3) and larger end user bandwidth improved the fidelity and reliability of internet radio.  The birth of common standards like Shoutcast made it possible to listen to many stations with a single player program, like Winamp.

Today, most music playback software supports streaming radio in some way.  iTunes features thousands of streaming radio stations and even supports Shoutcast streams so that users can easily add additional stations of their own.

The beautiful thing about streaming radio is the huge diversity in programming that is available.  Many college radio stations have a streaming server, like KDVSDigitally Imported hosts many electronic and dance music streams that give the listener the choice to listen to specific genres like ambient or gabber hardcore (whoa).  Broadcast radio usually lumps all electronic dance music into one category, much to the dismay of their listeners (who probably tuned out during the commercial break, anyway).  Gems like Slay Radio specialize in music you would never hear on broadcast FM, like Commodore 64 remixes.

In the past couple years, products have started to appear that mimic the form and function of a traditional radio, but play internet radio instead.  Good examples of these are the Roku SoundbridgeRadio and the ASUS Internet Air.  Remote speaker devices, such as the Apple Airport Express, require a PC to receive and relay streaming radio but achieve a similar end result (but don’t really look much like a radio).

The Wifi Radio project:

I have been wanting to build a streaming radio for some time.  I frequently work in my garage, where I occasionally use my Macbook to play music through a small amplifier and bookshelf speakers.  The problem is that my laptop is not always set up in the garage, and greasy fingers are not a good thing to have around a white laptop, period.  I could simply buy an internet radio, but I couldn’t stomach the $150-$300 price tag on most players for such a luxury.

So I decided to build one instead.

I started the design process by drafting an outline of desired features, and then breaking them down into wants and needs, while trying to keep the project scope under control.


  • Wireless connectivity through existing Wifi network
  • Audio output (preferably 44kHz, 16 bit stereo)
  • An integrated amplifier and speaker(s)
  • Shoutcast/MP3 streaming audio decode
  • Several builtin station presets
  • A display to indicate the station and currently playing song
  • Simple user interface, using standard radio controls (volume, tune, etc)
  • 110VAC operation

Optional features:

  • Line output (to connect to a receiver/amplifier)
  • Web server for configuration/management
  • Ability to play files off a USB stick or iTunes server

Definitely won’t be a feature:

  • Any kind of over-the-air radio tuner
  • Commercials
  • Pledge season
  • Morning DJ’s
  • “Blah, blah, blah.”

Now that we’ve defined the project…  it’s time for a commercial break.  That’s it for part 1 of this series.  Stay tuned for part 2, where I’ll talk about choosing an embedded platform for the design and why Linux is so awesome!

Update: Part two is now available, click here to see it!

Update 2: There is a new Wifi Radio Discussion Forum, hop over there to ask questions about the project or see what other people are working on!  (4/12/09)

Update 3 (6/1/09): I finally added a table of contents to the top of this post to help everyone (including me) navigate the series!