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television signals

RGuyserRGuyser Posts: 90
edited 2006-06-09 18:04 in Propeller 1
I havent purchased a propeller yet, but something mentioned in one of the documents i read about it made me very interested...

the line was something like:

" the stamp can even transmit wireless signals to televisions(sorry fcc)"


i am interested in what this statement means. not for nefarious reasons, for an art project idea ive got..

anyone know what i am talking about?

Thanks alot!

Robert

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2006-06-07 04:43
    Look at the "tv.spin" object that's part of "GraphicsDemo". The comments at the end very briefly indicate how you can produce modulated video with or without sound (using another cog). The output has to be on the lower VHF channels and you specify the frequency in MHz during initialization.
  • RGuyserRGuyser Posts: 90
    edited 2006-06-07 05:10
    so, this transmits through the air? the chip somehow "self modulates" the signal?

    crazy!

    and, because of the 8 cogs, i presumeone can send multiple streams?(though i suppose interfernece may be an issue...)

    thx.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-06-07 15:06
    You could transmit on different channels, at issue is the graphics.spin consumes a huge amount of memory and you could only fit one unique screen into the memory. However if you modified it so that the text-only version TV_text.spin were used, you could easily transmit on multiple channels.

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  • RGuyserRGuyser Posts: 90
    edited 2006-06-07 22:03
    any info on how this works? is this something i could recreate in a tiny 8-pin PIC micro? 12C series....

    i imagine this works by taking a signal and 'modulating' it at an appropriate frequency?
  • Mike GreenMike Green Posts: 23,101
    edited 2006-06-08 04:10
    I don't think that a PIC micro can do the I/O fast enough. The Propellor version makes use of both timer/counters that are part of each COG and they run off the system clock. For a PIC, you'd probably need an external carrier oscillator which could be a simple, cheap CMOS quad buffer and a crystal.
  • RGuyserRGuyser Posts: 90
    edited 2006-06-08 23:05
    thanks for all the responses...

    is there a website somewhere that talks about these techniques? i look forward to playing with a propeller eventually(like, when i can afford the development system), however, i am also very interested in a tiny device tha can display words on a tv screen with no battery...

    i was imagining a tiny PIC on a tiny PCB, and an antenna or whatever...

    is there a 'name' for this technique of signal transmission?
  • Tom WalkerTom Walker Posts: 509
    edited 2006-06-09 13:34
    RGuyser,
    "No battery"? I'm not sure what you think is going on, but there is indeed power being fed to the system...there is no "magic" going on....this is simply (but genius on a chip) an NTSC signal being synthesized and broadcast in more or less the same way TV stations do it...

    Or perhaps I'm missing your point...

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  • RGuyserRGuyser Posts: 90
    edited 2006-06-09 17:32
    tom,

    this 'with no battery' thing, it must be a typo. i think i meant to say '...with no special transmitting hardware', i know about batteries and how they make wind.. i mean power...

    the reason i am asking about this is i had an idea for a 'bottle', and when you open it, tv signals come out... or a fortune cookie, and when you crack it open, it gives you your fortune on a tv.

    the propeller chip is too expensive for what i would want to do sell these 'inexpensively' at my art shows. i think it is very intriguing that a small device could store and transmitt tv signals.. i immeddiately thought 'i wonder if any of the higher-end 8pin PIC\atmel MCUs could do this.'

    i was hoping there is a name for this technique so i can do my own research - google words to search on..... "ntsc synthesis" isnt going to do it. i figured this might have a special name, sort of like 'bit banging'. it makes me think of bit banging...

    YES. before someone tells me that bit banging is somethign else entirely, and unrelated, i understand that... it was an example of a way MCUs can generate specific signals which may normally require additional circuitry through default hardware tricks.


    (i am getting used to posting here... dont try and explain what you mean.. explain what you dont mean - so noone else explains it for you).
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-06-09 18:04
    This may help you understand the theory behind broadcast TV transmission: http://www.pembers.freeserve.co.uk/World-TV-Standards/index.html#Transmission

    The animated picture may help you visualize whats going on. Basically the base frequency of the channel chosen is modulated by the NTSC video signal, IOW the amplitude of the channel frequency is determined by the level of the NTSC signal.·The frequencies for the channels is easily searchable under "broadcast television channel frequencies".

    You may be able to find a processor capable of doing it if it has a specilized high speed counter whose amplitude can be·dictated in a high speed fashion. However, in my experience not many microcontrollers provide counters that are versatile enough to do this.

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    Post Edited (Paul Baker) : 6/9/2006 6:09:47 PM GMT
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