502Gate

DLink DSL-502T Based IGate

A project by Matthew Garside, VK6MRG and Rick Kowalewski, VK6XLR


The following is extracted from http://www.quicktrip.co.nz/jaqblog/home/30-dlinkigatepart1 by Andrew Quinn, ZL1WJQ

This project came about because a group of amateur radio operators in Auckland wanted to improve the APRS receive coverage by using IGates to add receive only coverage around South Auckland.
They found that a really low cost way of doing this (both initial investment and ongoing operational costs) was to use DLink DSL-502T ADSL routers with customized firmware.

The DLink DSL-502T is very common in New Zealand. It was the router of choice for many first time ADSL users who signed up with the large ISP’s.  Over time many users want devices with more capability (wireless or more ports) so the routers are available at very low cost (or free).

For those who care about the technical details…. the official specification for a DSL-502T is:

  • ADSL modem with ADSL2/2+ support to 24Mbit/s+.
  • Single 100MBps LAN port.
  • Single USB-B port (default firmware uses this to provide USB-over-ethernet to a PC host only, it’s not clear if this can actually be used as a USB host)
  • Flash chip: 4MBytes – Samsung K8D3216UBC a 32Mbit NOR-type Flash Memory organized as 4M x 8
  • SDRAM: 16Mbytes – Nanya NT5SV8M16DS-6K
  • CPU: TNETD7300GDU Texas Instruments AR7 MIPS based

More complete hardware details are on the OpenWRT DSL-502T hardware page.

In its IGate implement the ADSL modem or the USB-B port are not used.  What the specification doesn’t say is that there is an onboard serial port (even provided with soldered pin headers) which is perfect (with level conversion from RS-232 to 3.3V TTL) for connection to a TNC.

Using a DSL-502T as an IGate is as much an exercise of configuring software as it is connecting hardware.  The standard operating software makes the device an ADSL router…. so this is replaced to become an IGate.

The custom firmware is built and configured to achieve the following functions:

  • A standard set of firmware that can be flashed into many routers.
  • Installation without needing to connect to each router to install extra packages or make configuration settings (unless absolutely necessary).
  • For the router to be able to indicate it’s operational status using the front panel LED’s (only Status, Ethernet and USB are controllable… it appears that the ADSL indicator is managed directly from the ADSL interface).
  • Central management of the APRSD configuration and have this automatically applied whenthe power is cycled on the router.

The Project:

The ADSL modem circuitry is no longer required so all components associated with the telephone line interface are removed.

The miniTNC sits neatly where the line interface was.

It’s mounted on the serial port 5 pin header and secured to the back panel.

 

 

The miniTNC is based on the ATMega8 based TNC design from Henry Carl Ott (N2RVQ).  The firmware is a slightly modified version of N2RVQ’s version 1.8.  The difference is a startup delay to prevent the miniTNC transmitting via the serial port thus preventing the DSL-502T from booting.

 

The 502Gate will operate on either 12VDC or 9VAC.

It uses the ‘Tinytraker/ArgentData’ standard DB9 pinout.

 

Configuration files are stored on a central server, in this case http://www.mwarg.org.au
The 502Gate uses its MAC address to find the correct config file, ie 00:17:9A:DD:EE:FF.conf  When the 502Gate boots, it interrogates the server and downloads a copy of its configuration which it then saves internally.
During any subsequent boot, if the 502Gate can’t find the server, it will use the saved copy.

Should the 502Gate require any updates, the files can be remotely downloaded from the server.

The entire 502Gate network  can be viewed at aprs.fi

Availability:

MWARG have available for purchase:

  • complete 502Gates, minus radio
  • pre-built miniTNC’s
  • blank PCB’s for miniTNC’s
  • programmed microcontrollers.

References:

Information and firmware provided by Andrew Quinn, ZL1WJQ
http://www.quicktrip.co.nz/jaqblog/home/30-dlinkigatepart1
OpenWRT DSL-502T hardware page.
http://wiki.openwrt.org/oldwiki/openwrtdocs/hardware/d_link/dsl_502t
ATMega8 based TNC design from Henry Carl Ott

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