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Prop to Prop wireless comms using TV Broadcast mode - Is it possible ??? — Parallax Forums

Prop to Prop wireless comms using TV Broadcast mode - Is it possible ???

Cluso99Cluso99 Posts: 18,069
edited 2011-12-09 07:39 in Propeller 1
I was thinking (dangerous at any time!) about comms from my Quadcopter to ground to look at the data being received from the gyro (and later the accelerometer). It would be nice to display this on a small TV monitor (a car camera display which I bought for $26). So I began to think of ways to send this data.

Then I thought about the work Phil (PhiPi) has done with decoding radio signals simply with the prop. For now, I only need one way comms, and short distance <10m.

So...

Prop 1:
Uses the Broadcast mode to transmit a TV signal. Now, the video data can be simplified to monochrome and each line could be an 8 bit value. Easily done with 3 or less resistors.

Prop 2:
Acts as a receiver, demodulates and extracts the 8 bit values, and displays them on a composite TV.
I am not sure, but I think the work Phil has done would permit the decoding to be done in software quite simply with just a few parts (R, C & L).

@PhiPi: Do you think this is possible???

Comments

  • PerryPerry Posts: 253
    edited 2011-12-06 13:39
    You might consider modulating the audio channel with the APRS software but it is only 1200 baud.

    Personally I prefer visualizations over data dumps, you might get some ideas from my old "On Screen Drone project" http://forums.parallax.com/showthread.php?95870-Propeller-OSD-Drone&highlight=screen+drone for some display ideas re: instrumentation.

    Perry
  • VIRANDVIRAND Posts: 656
    edited 2011-12-07 15:34
    In this case it seems simplest to forget about the second propeller and just transmit directly to the TV.
    If there is a need to receive data from the video channel then you might start by transmitting binary using
    white squares at the top of the screen as the ones and spaces for the zeroes. The only simple receiver
    I can think at the moment is to use a VCR as a tuner or use whatever else has an antenna input and video output.

    Video channels have extremely high bandwidth and cannot fit in other frequencies.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-12-07 19:23
    You could use closed-captioning to send and display text:

    -Phil
  • PerryPerry Posts: 253
    edited 2011-12-08 11:57
    Phil Pilgrim (PhiPi) wrote: »
    You could use closed-captioning to send and display text:

    -Phil

    I was about to offer that idea too, but instead of close caption data, one could send other data on the unused lines below line 20 and have a Prop with a sync separator decode your own protocol, you could possibly get 16 words sent at 60fps?


    Perry
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-12-09 00:57
    Phil: I was thinking that the prop could perhaps demodulate the signal along the lines of what you have done to receive radio. I am not familiar enough with the TV counters to know if that could be used to modulate a signal that could be demodulated by another prop, just yielding a low rate set of data.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2011-12-09 01:18
    I suppose that you should stay off of TV broadcast channels and find another frequency band for Propeller RF transmission and reception. Of course, the world is going to digital TV and it just may be that the analog TV bands will be let open for hobby fun. But we are not quite there yet. Demodulations shouldn't be too hard - in many cases it just requires a diode and a few components. Of course, you may need an op amp at the front end to boost the signal to being adequate for further processing.
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-12-09 05:55
    Without a proper aerial and rf amp its not likely to interfere w tv reception. In Oz analog tv is being switched off around the country now. Ours goes in 3 mths.
  • Jorge PJorge P Posts: 385
    edited 2011-12-09 07:18
    You might want to keep an eye on the following FCC test site for TV Frequency White Spaces, http://whitespaces.spectrumbridge.com/Trial.aspx the trial just ended but it will eventually allow communications on unlicensed frequencies. There are links to other things you might want to use, eg. to select an open TV frequency no longer used in your area.

    that is within the United States. Other countries may have something similar.
  • SarielSariel Posts: 182
    edited 2011-12-09 07:24
    I was talking with a friend about the digital conversion, and he said something along the lines of the reason why they are going to digital TV is because the FCC wants to free up that bandwidth for other things because the spectrum is getting too crowded in those frequencies.

    He is the kind of guy that studies signals and packet information for fun... WAAAYY out of my comfort zone, so I could be wrong, mis-quoting, or getting bad information to begin with. I just wanted to say, it might be a good idea to look into it a little bit before you make a mistake that will have (insert your country's federal agency here) knocking on your door. But, I do know, for short range stuff, you are probably safe as long as you don't crash any aircraft or disturb a hospital with your project.
  • Jorge PJorge P Posts: 385
    edited 2011-12-09 07:39
    @ Sariel

    The homepage of the site I linked to above has that notice. The bands are being slowly freed up on an area by area basis, although some are not for portable devices, only fixed. Do a "Whitespace Spectrum Search"

    EDIT, sorry its not their homepage it is the overview page http://spectrumbridge.com/WhiteSpacesSolutions/Overview.aspx
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