The new Propeller Backpack module with Pal ( Not NTSC)

Joe

Hi,

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 Green

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

Joe

Hi,

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

Do you know if the Backpack module could work ?

Thanks, Joe

Mike Green

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)

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.

-Phil

Joe

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 :


http://www.hittconsulting.com/hcosd.htm


Joe

Mike Green

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.

Joe

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:


http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropellerBackpackv1.0.pdf

Could confirm please, thanks, Joe

Mike Green

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.

Joe

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

marcwolf

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
Dave

Ltech

@"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 ???


NTSC
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


PAL
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