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Thread: Capture, transmit & display RCA video with prop & xbee

  1. #1

    Default Capture, transmit & display RCA video with prop & xbee

    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

  2. #2
    Cluso99's Avatar
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    Default Re: Capture, transmit & display RCA video with prop & xbee

    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.
    My Prop boards: CpuBlade, TriBlade, RamBlade, www.clusos.com
    Prop Tools (Index)
    Emulators (Index) ZiCog (Z80)
    Prop OS (also see Sphinx, PropDos, PropCmd)

  3. #3

    Default Re: Capture, transmit & display RCA video with prop & xbee

    At a maximum data rate of 250 kbps, the XBee is too slow (by several orders of magnitude) to transmit real-time video.

    -Phil

  4. #4

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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.
    Click image for larger version

Name:	LedHi.jpg
Views:	66
Size:	118.7 KB
ID:	85348

    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

  5. #5

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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

  6. #6

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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.

  7. #7
    Cluso99's Avatar
    Location
    Sydney/Brisbane Australia or 'sailing on the high seas'
    Posts
    10,060

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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.
    My Prop boards: CpuBlade, TriBlade, RamBlade, www.clusos.com
    Prop Tools (Index)
    Emulators (Index) ZiCog (Z80)
    Prop OS (also see Sphinx, PropDos, PropCmd)

  8. #8

    Default Re: Capture, transmit & display RCA video with prop & xbee

    Quote Originally Posted by JBWolf View Post
    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 Déjà vu.
    Last edited by Duane Degn; 09-24-2011 at 08:16 PM.

  9. #9

    Default Re: Capture, transmit & display RCA video with prop & xbee

    I dunno much about the XBee's, do they offer an analog pass-through mode? if so whats the bandwidth?
    Good to finally be in CA!

  10. #10

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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.

  11. #11

    Default Re: Capture, transmit & display RCA video with prop & xbee

    @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..
    Good to finally be in CA!

  12. #12

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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
    Last edited by JBWolf; 09-26-2011 at 07:16 PM.

  13. #13

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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

  14. #14

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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?Inv...310A-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/tx...4/Default.aspx

    -- Gordon

  15. #15

    Default Re: Capture, transmit & display RCA video with prop & xbee

    Quote Originally Posted by RinksCustoms View Post
    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

  16. #16

    Default Re: Capture, transmit & display RCA video with prop & xbee

    ah I'm sorry.....
    I have 2 threads going, one for video and one for motors.... posted in wrong one lol

  17. #17

    Default Re: Capture, transmit & display RCA video with prop & xbee

    Quote Originally Posted by GordonMcComb View Post
    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?Inv...310A-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/tx...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

  18. #18

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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

  19. #19

    Default Re: Capture, transmit & display RCA video with prop & xbee

    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/

  20. #20

    Default Re: Capture, transmit & display RCA video with prop & xbee

    Quote Originally Posted by JBWolf View Post
    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

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