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The new Propeller Backpack module with Pal ( Not NTSC) — Parallax Forums

The new Propeller Backpack module with Pal ( Not NTSC)

JoeJoe Posts: 184
edited 2011-01-04 21:08 in Learn with BlocklyProp

I need the Propeller Backpack ( Item code 28327 ) .
I want to use it with a Basic Stamp.

My problem is that I need to use it with
a PAL ( Not NTSC) signal.

It seems that it is possible to use with PAL
and I just have to modify some resistors.

But my problem is that I don't understand how
to replace these resistors.

Please help. , Joe


  • Mike GreenMike Green Posts: 23,101
    edited 2010-02-12 18:56
    If you're using the Backpack for PAL output (not overlaying), you just have to modify the TV driver. You don't have to change any resistors. Look at the comments at the end of TV.spin (the standard low-level TV driver). This comes with the Propeller Tool. There's a description of the various configuration bits including the one for NTSC vs. PAL (tv_mode bit 0). Also look at tv_text.spin which displays text on a TV and contains the constants used to set the configuration bits used by TV.spin.

    Post Edited (Mike Green) : 2/12/2010 7:01:30 PM GMT
  • JoeJoe Posts: 184
    edited 2010-02-12 19:01

    I need to use it to overlay the data from a GPS.

    Do you know if the Backpack module could work ?

    Thanks, Joe
  • Mike GreenMike Green Posts: 23,101
    edited 2010-02-12 19:37
    The current Backpack video overlay software is written only for NTSC. I'm sure it could be modified for PAL use, but that would be non-trivial. Like I said, the existing Propeller video drivers can be used to produce PAL output with the Backpack, but not overlaying.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-02-12 20:53
    As it was with NTSC, overlaying PAL with the Backpack should, theoretically, be easier than originating PAL, since the overlay program doesn't generate any sync signals or color bursts on its own. It derives its sync from the incoming video, and passes the sync and color bursts through without modification. So the only thing that may need to change in the overlay program is how sync pulses are counted and the timing from the beginning of the scan line to the front porch, where the program clamps the black level and waits for the next sync. This will also entail recomputing the text centering and right-alignment functions, along with the maximum text width limitation. Although I'm confident that the overlay program could be modified to accommodate PAL, I have no way to test such a scheme here, since all my video stuff is NTSC.

  • JoeJoe Posts: 184
    edited 2010-02-12 21:05
    I am sure that it is possible. But very difficult.

    I found a similar module that uses the Propeller too and
    overlay PAL and NTSC :

  • Mike GreenMike Green Posts: 23,101
    edited 2010-02-12 22:06
    If you can find one of Bean's (Hitt Consulting's) HCOSD boards, it's supposed to work with PAL. I've used one with NTSC and it worked very well. Unfortunately Bean is no longer making or selling his products. The schematics and software is available on Bean's website so you could make your own board and use his software. You might be able to use his software as a guide to changing the Backpack's software.
  • JoeJoe Posts: 184
    edited 2010-02-12 22:23
    Thanks Mike:

    But ,
    it seems that you think that it is a software change and not a hardware change.
    I can read at page 23 of the Backpack manual that there are some resistors
    for PAL use:

    Could confirm please, thanks, Joe
  • Mike GreenMike Green Posts: 23,101
    edited 2010-02-13 00:07
    The resistors form a DAC (digital to analog converter) used to produce the video signal (sync pulses and white to black levels). They are the same for PAL or NTSC. No resistor changes are necessary.

    The differences between NTSC and PAL mostly have to do with timing as Phil mentioned and that's completely controlled by software.
  • JoeJoe Posts: 184
    edited 2010-02-16 13:48
    Hi, thanks a lot for your helps.

    I tried to overlay my PAL camera video with the Parallax Backpack module
    but I can't.

    I am not an expert . I think Parallax could try to develop some
    software for PAL users.

    Parallax has many European customers and perhaps Parallax Engineers
    could develop a software or code for European customers.

    It is a suggestion only, maybe it is too difficult to do it.

    Any way thanks again , Joe
  • marcwolfmarcwolf Posts: 38
    edited 2011-01-04 21:08
    I'd be very interested in an update to this.
    I've just brought a Propeller Backpack for the sole purpose of using it as a OSD, and would prefer not to go through learning a new micro language.

    Many thanks
  • LtechLtech Posts: 366
    edited 2020-05-07 10:25
    @"Phil Pilgrim (PhiPi)" , Can you explain the numbers relation to NTSC in you code please, I try to get sync out of PAL video, not NTSC
    With not modified "prop_backpack_tv_overlay2.spin" I can overlay in PAL, but the overlay flash 2-3 time/sec, not constant.
    It locks, but not steady.
    I believe if I have you relation of this numbers, I can apply it in PAL video.

    Thank you
    half_sync     long      1200
    even_odd_thld long      -3840
    line_thld     long      960
    frontporch    long      80 * 62

    In you code, you use som constants, can you give the relation of you numbers with the NTSC timings
    Dit you find them empiric, or are there som math behind?

    half sync 1200 => 4,us/2 = 2,35us ???
    even_odd_thld => even odd detection ?? is neg ?
    line_thld => line detection ?? NTSC= 560 ?
    frontporch 80*62 => 4960 => 1,5us ???

    Abbreviation National Television System Committee
    Video Bandwidth 4.2 MHz
    Sound Carrier 4.5 MHz
    Bandwidth 6 MHz
    Vertical Frequency 60 Hz
    Horizontal Frequency 15.734 kHz
    Color Subcarrier Frequency 3.579545 MHz
    Lines/Field 525/60

    Abbreviation Phase Alternation by Line
    Video Bandwidth 5.0 MHz
    Sound Carrier 5.5 MHz
    Bandwidth 7 to 8 MHz
    Vertical Frequency 50 Hz
    Horizontal Frequency 15.625 kHz
    Color Subcarrier Frequency 4.433618 MHz
    Lines/Field 625/50
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