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Capture, transmit & display RCA video with prop & xbee — Parallax Forums

Capture, transmit & display RCA video with prop & xbee

JBWolfJBWolf Posts: 405
edited 2011-09-29 21:10 in Propeller 1
Hello,
I would like to learn how to capture video via RCA plug on one prop chip, and transmit it via xbee to another prop chip, which would be RCA out to the 7" TFT sold by parallax.
Basically a wireless security camera with dedicated video screen on the receiving prop chip.

I have RCA jacks, 2 props & 2 xbees.... but cannot find any information on how to transmit video, I can only find info on using the RCA as an output to generate custom graphics.

I do not need to record or manipulate the video, simple transmission would be great :)

Comments

  • Cluso99Cluso99 Posts: 18,069
    edited 2011-09-24 10:58
    Sorry I cannot help with much of this so perhaps someone else will chime in.

    The tv output is quite simple as you will just place the received data continuously into the hub screen buffer with a seperate wireless cog. As for transmitting, you will use a cog to repeat sending a copy of the received screen buffer. You may need to place a delay between each transmission to avoid too much flicker between screen updates.

    Hopefully there may be some sample code either in obex or in the wireless forum section for transmitting and receiving data via zigbee.

    IIRC there has been a thread on receiving tv so try a search for this.

    Oh, and I see you are new, so welcome to this fabulous forum and the prop.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-09-24 10:59
    At a maximum data rate of 250 kbps, the XBee is too slow (by several orders of magnitude) to transmit real-time video.

    -Phil
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-09-24 11:49
    JBWolf,

    Welcome to the forum and welcome to the world of limited bandwidth. As Phil said (and he's an expert about such things(and many others)) XBee's just don't come close to being able to transmit all the data in a video signal (in real time).

    The easy way around this problem is to buy a video transmitter/receiver set (I think DealExtreme has some).

    It may be possible to transmit a very low resolution image with your XBees. I've wondered about doing this myself. I used Hanno's video capture method and lowered the resolution of the image to a 12X10 8-Bit grey scale image. This limits the data per frame to 120 bytes which I think is low enough to send real time with an XBee. Of course the pictures aren't much to look at. By decreasing the frame rate you could increase the resolution per frame.

    This is definitely the hard way of doing things. I've just had these things on my mind so I thought I'd share them.

    Here's an example of a 120 byte image. There's a video camera in the top left corner. The "HI" on the whiteboard is being displayed on the LED array.
    LedHi.jpg


    This is part of a another project I'm working on.

    There are other wireless devices that have higher data rates than XBees. One of the forum members uses them to transmit audio (which is much easier than video).

    Duane
    LedHi.jpg
    489 x 480 - 119K
  • JBWolfJBWolf Posts: 405
    edited 2011-09-24 12:27
    haha thats a pretty cool led screen... I think I saw something like that at an art museum that took up a whole wall, you could make out peoples silhouettes and if close enough, facial features.

    How about 1/2 second BW captures?

    I just found this.... gonna read later when I have time:
    http://forums.parallax.com/showthread.php?86376
  • JBWolfJBWolf Posts: 405
    edited 2011-09-24 12:29
    oh I remember now.... the art thing did work like that... but it wasnt LED's, it was servo actuated 'flappers'.
    Each servo had a square peice of brown paper attached that would tilt to a certain angle to represent a shading.
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-09-24 12:35
    I had not thought much about bandwidth, more about flicker. The prop would have some reserve processing power for compression and not having to transmit unchanged pixels may help too.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-09-24 12:58
    JBWolf wrote: »
    I just found this.... gonna read later when I have time:
    http://forums.parallax.com/showthread.php?86376

    Wow, How did I never see that thread before? My only excuse is the thread is from before I started learning about microcontrollers.

    Thanks for the link. I've got some reading to do.

    Duane

    Edit: I skipped to the end. I think I had seen it before. The end of the thread gave me a strong feeling of D
  • RinksCustomsRinksCustoms Posts: 531
    edited 2011-09-24 14:47
    I dunno much about the XBee's, do they offer an analog pass-through mode? if so whats the bandwidth?
  • Mike GreenMike Green Posts: 23,101
    edited 2011-09-24 15:28
    RinksCustoms,
    Even if the xBees used analog modulation, a modulator would have to be designed specifically for video use to be effective over that frequency range. You really have to use a transmitter and receiver designed for video use.
  • RinksCustomsRinksCustoms Posts: 531
    edited 2011-09-25 11:19
    @Mike - yeah, that's what I was getting at. I know transmitting video requires high bandwidth amplifiers w/low THD % (ie- transmitting ch 2 @ 55.25MHz, you need a transmitter amp with ~165-200MHz bandwidth) for a clean broadcast. I suppose that the prop at the camera wouldn't be easily able to use a sync separator to modulate the ntsc video signal from the camera, but then the prop at the recieving end would have to demod the signal for the tv monitor at the other end.. perhaps mouser has some cheapy video transmitter/receiver boards.

    @jbwolf, welcome to the forums - regarding on how to transmit video, there's a few settings you need to change in the "tv_params" that you coppied from the tv driver down in the DAT section of your program that will tell the tv driver to transmit broadcast instead of just RCA baseband. If you open the tv.spin driver and look down at the bottom it shows you an explanation of the parameters and which bits to set for what video format you want, on which pin group you want, even which nibble (high/low nibble of a pin group of 8), NTSC/PAL, interlace, broadcast/baseband/S-Video..
  • JBWolfJBWolf Posts: 405
    edited 2011-09-26 11:20
    How do I send information to 2 cogs at the same time?
    I can draw straight lines with the previous code... but I cannot get it to move in a diagonal

    Thanks for all the help :)
    Not really sure what to do about video yet... I'm going to search for a dedicated ntsc transciever as I do not think the propcam can provide enough resolution for a security camera
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-09-26 11:44
    JBWolf,

    The information in most serial objects ends up in hub RAM where any cog can access it.

    What is "the previous code". (You're not giving us very much information.)

    Duane
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2011-09-26 12:21
    Unless you're looking at this as an exercise in discovery, since you're not manipulating the video there's no point in doing it this way. You want one of these:

    http://www.geeks.com/details.asp?InvtId=RC310A-CM260CWAS

    That way you can skip the cost of the two Propeller's, two XBees, the video digititizer on the transmitting end (remember, you're starting with analog video and then want to broadcast it digitally), and the decoder on the receiving end.

    The VIDEO OUT of the wireless receiver will connect to the 7" monitor.

    If you're looking to add a text overlay to the received video you want one of these:

    http://www.parallax.com/tabid/768/txtSearch/28327/List/0/SortField/4/Default.aspx

    -- Gordon
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2011-09-26 12:23
    RinksCustoms wrote: »
    I dunno much about the XBee's, do they offer an analog pass-through mode? if so whats the bandwidth?

    You might be able to modulate one of the analog pins and then read its corresponding pin on the receiver but that would be very counter productive. Not sure you'd get a bandwidth even high enough for decent audio.

    -- Gordon
  • JBWolfJBWolf Posts: 405
    edited 2011-09-26 13:10
    ah I'm sorry.....
    I have 2 threads going, one for video and one for motors.... posted in wrong one lol
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-09-26 13:13
    GordonMcComb wrote: »
    Unless you're looking at this as an exercise in discovery, since you're not manipulating the video there's no point in doing it this way. You want one of these:

    http://www.geeks.com/details.asp?InvtId=RC310A-CM260CWAS

    That way you can skip the cost of the two Propeller's, two XBees, the video digititizer on the transmitting end (remember, you're starting with analog video and then want to broadcast it digitally), and the decoder on the receiving end.

    The VIDEO OUT of the wireless receiver will connect to the 7" monitor.

    If you're looking to add a text overlay to the received video you want one of these:

    http://www.parallax.com/tabid/768/txtSearch/28327/List/0/SortField/4/Default.aspx

    -- Gordon

    Gordon,

    In the example I was sharing about the LED array, it is pretty much an "exercise of discovery".

    One of my long term projects is to use a RC heli to take aerial photographs (I've done this a lot (and semi-professionally) with fixed wing aircraft in the past). Several years ago I purchased one these video links. My understanding is 900MHz provides better distance than 2.4GHz. I also have a Propeller Backpack. My plan is to overlay telemetry information onto the video signal before it's feed into the transmitter. I also have a pair of 900MHz XBees. I'm not sure if the XBees signal will interfere with the video signal or not.

    If the XBees work well enough I could use the Backpack on the ground to overlay the received telemetry on the ground-station screen (so I don't need a separate displays for both video and telemetry).

    My day job and many side projects have kept me from testing the various equipment together. (I'm probably delaying flying all my expensive equipment at once out of fear of a crash as well.)

    Duane
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2011-09-26 13:46
    I have a project where I've taken a vehicle backup camera, spliced a Backpack between the camera and transmitter, and receive that on a monitor. It's a 2.4 GHz video transmitter AND I've sending remote control via 2.4 GHz XBee. Interference is marginal, but the video transmitter has four channels, and at least two of the channels are far enough away from the center frequency of the XBee that the signal is not degraded.

    The biggest issue is non-conformance of the video output of the backup camera. It's not 1v p-p, but I've tweaked the interface circuit a bit to improve performance. A better camera and transmitter would result in a much better picture.

    For my project the data is environmental info collected from a bunch of Parallax sensors. The Backpack makes overlaying the data extremely easy. (After I realized the Backpack didn't come overlay-ready. The required download to change the firmware is on the Backpack page.)

    -- Gordon
  • JBWolfJBWolf Posts: 405
    edited 2011-09-28 13:35
    Sorry to jump off topic for a sec, thought Duane might like to see this:
    The camera is the small black spot just above the center.
    http://www.wimp.com/woodenmirror/
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-09-28 15:21
    JBWolf wrote: »
    thought Duane might like to see this:

    You're right. That's very cool.

    That makes soldering 120 LEDs onto a board seem very quick and easy by comparison.

    Thanks for the link.

    Duane
  • JBWolfJBWolf Posts: 405
    edited 2011-09-29 15:48
    I am absolutely more interested in discovery and education.
    One analogy comes to mind: You can't build a house on a weak foundation.

    I have come to the conclusion that realtime color video through the propelIer is not possible, so I think you presented the solution for my needs Gordon, thank you!
    I will still have to use 2 xbees as I am making a PTZ camera for surveillance rather than a network static cameras.
    Only thing I cant figure out... how do you splice the backpack ontop a video stream to get a single output? just a simple RCA splitter?
    I would like to timestamp the recorded video.

    Duane, I'd be a little wary about 900mhz nowadays. I have had so many interference problems... most commonly, cordless phones corrupting data on DSL lines typically making the modem disconnect and causing false signals (wicked sounds) on the phones at the same time. I bet if you put a 900mhz phone between the transmitter and receiver, 60% chance your heli would drop out of the sky.... or worse
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-09-29 16:37
    In overlay mode, the Propeller Backpack has a video input and a video output. The camera feeds the input, the Backpack overlays character data, and sends the overlain video to the output. Both input and output happen at the 1/8" stereo phone jack. If you use RCA connectors, you will need to get one of these:

    or one of these:

    -Phil
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-09-29 16:42
    JBWolf wrote: »
    Only thing I cant figure out... how do you splice the backpack ontop a video stream to get a single output? just a simple RCA splitter?
    The BackPack has video in and video out. You put your video signal into the backpack and what comes out is the same signal plus the overlay. You can't just splice two video signals.
    JBWolf wrote: »
    60% chance your heli would drop out of the sky.... or worse
    The 900MHz XBees would be used for telemetry not for control. I'd use my normal helicopter transmitter to control the helicopter.

    Duane

    Edit: Phil beat me to it about the BackPack.
  • JBWolfJBWolf Posts: 405
    edited 2011-09-29 21:10
    Wow the backpack is quite straightforward! I foresee several of these in my hands in the near future

    lol sorry duane, did not think about that. I see the 60mw xbee pro has a listed outdoor range of 1 mile though!
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