APRS Position & Messaging for OLPC

Bob Bruninga, WB4APR, US Naval Academy Satellite Lab, Annapolis, MD

APRSXO written by Jack Zielke, KG4GJY, is now available.

APRS Universal Messaging Initiative: Putting a minimum APRS capability onto the OLPC XO laptop is just one part of the Universal Ham Radio Messaging Iinitiative. . We want all wireless devices to be able to be used for text-messaging between ham radio operators by callsign-alone. The XO is an excellent wireless PC for such an application whenever it is in range of a WI-FI network. .

Here are Jack's instructions on how to download and install APRSXO on your OLPC. Probably better now that he has his own web page to go there for details.

  • 1. start the Browse activity on your XO;
  • 2. go to the APRSXO web page;
  • 3. click on the latest APRSXO-N.xo bundle next to the word Download:
  • 4. when it's finished, click OK on your XO.
  • 5. press the Home key (fifth from the upper left) to see the taskbar on your XO.
  • 6. scroll the XO taskbar to the right (by clicking on the arrow ) until you see the icon for the activity; click on it to start.

    When the downloads finishes you should have a new icon on the tray bar. It will be at or near the end. Run the activity and check into APRS from anywhere (WI-FI)

    APRSXO Project: . This web page was drafted early in 2008 to lay out the design objectives of such a minimum APRS messaging client on such a device. The project consists of these major elements:

  • A web based APRS map page dedicated to the location of all XO's. Click here for the FINDU version
  • An APRSXO application that sends a position report into APRS once every 10 minutes while the XO is active. (Jacks APRSXO does this).
  • The APRSXO application will also receive incoming APRS messages addressed to this laptop. (Jacks APRSXO does this).
  • The APRSXO application will allow sending an APRS text message. (Jacks APRSXO does this).

    The map below could be representative of such a web page. (it is a fake).

    But the FINDU APRSXO web page is real, because APRS has defined a special symbol for the XO so that FINDU can select them. . In APRS, we suggest the XO laptop use an "X" overlayed on the Alphabetic Box, which is specified in APRS as the "XA" symbol.

    USER INTERFACE: . The image below was a concept dialog-box for how the user would set up his XO client parameters. Jack did a great job on implementing this in APRSXO.

    APRS WIRELESS DEVICE IMPLEMENTATION: . The following items detail the approach needed to design and implement something like APRSXO on any WIFI, Cell phone, Palm device or wireless laptop system. First all amateur radio XO's should the XO symbol so that they can be displayed on APRS such as on the FINDU System . Second we need the application to send a formatted line in the APRS format and inject it into the APRS Internet System (APRS-IS). The above set-up parameters will be formatted as follows:

  • MYCALL>APOLPC:=DDMM.mmNXDDDMM.mmWA Name's Home XO. Text goes here...

  • MYCALL: . Where MYCALL is your amateur radio callsign.

  • DDMM.mmN DDDMM.mmW: This is the Latitude and Longitude in degrees and decimal minutes. . If zip code lookup is used, then the "mm" in Latitude and Longitude are replaced with two space characters to signal a one-mile ambiguity in the position.

  • MAP SYMBOL: The special symbol for OLPC consists of two bytes. First the "X" between the lat/long and the "A" after the longitude. . We want all XO's to be forced to use the symbol for the XO. . If this application is run on any other PC, then the user is allowed to enter any of the other hundreds of APRS symbols as appropriate.

  • Name: . The name from the dialog set-up box is used with an apostrophy "'s " added. and combined with the word representing the kind of station from the dialog box followed by a period. This is just the default text if the user enters no other text.

    Text: . The user can enter any other free text if he likes to either replace the "Name's home XO." or to add onto the end of the free field.

    CONCLUSION: . Using these kinds of simple APRSXO applications will be a great way for OLPC users and any other wireless device users to find each other and for them to find local MESH's to join. . In fact, it is a great Application for EVERY ham radio operator with an wireless device!.

    WB4APR, Bob