Harry Potter Marauders Map Realized


After reading about cheap wireless for microcontrollers, [Leigh] left a comment about his Marauders map. Much like the Harry Potter version, whoever holds the ‘map’ is able to see the location of the ‘marauders’ within certain bounds. Unlike the magical version however, each person being tracked needs to hold a PICAXE 08M, GPS, and 433.92MHz transmitter: while the map needs a computer running his Python script and a receiver of the same frequency. It has the potential for locating people, but we feel it might be better off in a swarm robotics setup.

19 thoughts on “Harry Potter Marauders Map Realized

  1. imagine if you could tap into stuff that’s already constantly pinging gps in a network.

    gm’s onstar cars? instantly know traffic conditions without having access to dot radar stations. blackberrys? easily find concentrations of business travelers. iphones? now you know where to advertise the farmer’s market. etc.

  2. It would be illegal however to do this, im pretty sure. I think cellular radio communications are protected by the FCC, I know they are at least with scanners and voice traffic…. I don’t know about data over a cellular transmission.

  3. You can’t interfere with the signals and jam them or anything, but the air is still free and the electromagnetic waves traveling through you or your property can be freely absorbed and any information disseminated is public domain. It’s no different than if I was shouting out my window to my neighbor, just over the electromagnetic spectrum.

    Now if you broadcast on an ‘unauthorized’ bandwidth or subsequently jam any ‘legal’ signals then they get pissed and ‘fine’ you ‘a million dollarz’ or something, but I’m pretty sure that his exact frequency, although in the block allocated for digital transmission, most likely resides in one of the many white space gaps inbetween channels, being as how it’s quite a specific frequency.

    Just speculation however…

  4. Ok; I read up on the ‘laws’ (aka: whatever the FCC decides it wants to enforce) and apparently it’s also “Illegal to monitor remote radio-TV broadcast signals”… so.. your television is illegal… or maybe it’s illegal to make a television that doesn’t have an FCC stamp on it.. I’m not sure, probably whatever’s more convenient for them..

    So ok, you may be violating an FCC law, but are you ‘really’ committing a crime that’s going to be enforced? And if you aren’t broadcasting on a registered spectrum or anything then it’s pretty tough to get caught since you aren’t interfering with anybodies stuff.

  5. I looked into it more and to actually go through and monitor cellphone information (it’s encrypted) is a pain in the ass anyways – but alot of cellphones use standard gps I think, and I know you won’t have jackboots on your doorstep if you’re just trying to interface with gps satellites, so… figure it out – mabye use the cellphone’s internet connection to transmit its gps data to a server somewhere…

    way too much thought is going into this….

  6. I did this project for the 2009 Maker Faire for the National Association for Amateur Radio (“ARRL”) booth.

    Thanks for all the comments, especially the first one comparing the project to APRS.

    My idea was to show how to combine parts and techniques from the MAKE/DIY world with the ham radio world. There’s a significant overlap, both in interests and in individuals, and I felt that a project bringing something from each together would help cross the bridge in both directions.

    I didn’t see it mentioned in the write-up, but there are some Youtube videos of both the MM project and some APRS projects at the Maker Faire:

    For Part 1 (the Marauders) see
    For Part 2 (the Map) see

    If you’re interested in doing something like this, but with more range, consider getting a ham radio license and trying out APRS.

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