Unstable Video

Philldapill

A while back, I made a little video adapter that consisted of the 3 resistors, and a male AV plug. I use it to plug into my propeller breadboard sometimes, and it has worked fine. I recently fried that propeller, so now I have to resort to using a protoboard until my new chips arrive.

My problem is on every pin(multiple of 4, eg 0, 4, 8, 12, etc.). When I try to output video, it puts out the top left corner of the screen; the image is larger than normal, grey, grainy, and unstable(image skews back and forth).

Any ideas what could cause this? It happens with my adapater, AND· resistors soldered to the board. I know I have a good ground, so that isn't it. Very frustrating...

Mike Green

Sounds like something changed in terms of your software. Make sure the _CLKMODE and _XINFREQ are correct. The Protoboard uses a 5MHz crystal. I use a Protoboard with the standard 4 resistors on pins 12-15 for video and it works fine.

Philldapill

4 resistors you say Mike? My understanding is that the simply make a DAC for the video output. My values are 220, 429, and 875. I know they are odd values, but are approx. multiples of 2. Should I add a forth?

By the way, I'm using standard stal1 + pll16x, and xinfreq of 5mhz. I tried reversing the crystal, but it didn't do anything, just like I thought it wouldn't.

Philldapill

Well, it would be good to know what WAS wrong, but I just touched a Vin wire to the 3.3V. That Propeller is crispy now.

Mike Green

Crispy as in toast? Condolences!

The 4th resistor was in case I wanted to use broadcast audio. It's not needed for baseband video.

The resistors I used are 1K, 560 Ohm, 270 Ohm, and 560 Ohm, almost the same as on the Demo Board.

Leon

Is it an NTSC or PAL TV? That could be the cause of the problem.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Philldapill

This TV is NTSC. I've tried the board on two seperate TV's with the same output. I haven't changed any code from my previous board which worked fine. It was something strictly hardware about this board.

Leon

Have you checked that the outputs are working OK?

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Philldapill

I hooked the outputs up to a scope and they check out just fine. This problem with the screen is on every pin combo. I've tried it on pins 0-2, 4-6, 8-10, etc.

Is there a video generating circuit in every cog, or just one for the chip? I've modified my code a little so that the TV object gets loaded into different cogs each time, but it still didn't work. The chip is fried now(crossed Vin to 3.3V, Oops!), so it's not a big issue anymore, but I still appreciate the input.

Leon

There's one in every cog and the TV object uses the first one available. If your chip was still working you could modify the software to use a different one.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Post Edited (Leon) : 6/19/2008 5:44:43 PM GMT

Philldapill

Yes, Leon, I did that too... I had 3 objects running, 2 ADC's and the TV Object. I tried initializing the TV first, then ADC's, then an ADC - TV - ADC, then ADC - ADC - TV... nothing changed the output. This is all just very strange as my regular DIP propeller worked fine on the same TV, same program, same adapater. The only difference I can think of, is the DIP prop was runing off a 12V battery, and the bad prop was running off a walwart(~13V).

Phil Pilgrim (PhiPi)

Are you sure you connected the resistors in the right order? Highest value goes to the lowest port number. Also make sure the connector shell has a good ground connection.

-Phil

Bob Lawrence (VE1RLL)

I used a Protoboard and wired it for video out using the schematic for the developer board. At first I only used the 3 resistors on pins 12 (1.1K), 13 (560) and 14(270). It worked great! When I tried a broadcast experiment I added the 4th resistor on pin 15(560). Everything worked each time. I posted a basic hello world that will work with the 3 resistors to start with. Also note that it is for setup for NTSC. As Mike and others have indicated the 560K (on pin 15) is only used for aural subcarrier in the broadcast mode. It's also noted on the schematic.

Developer board schematic
www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropDemoDschem.pdf

CON

_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000


OBJ

text : "tv_text"      




PUB start | i

  'start term
   text.start(12)
              
 

   text.str(string(13,$C,7,"            Hello World",$C,4))

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Aka: CosmicBob

Philldapill

Phil,
Yes, I connected them in the right order. I was originally using the same(working) adapter from my DIP breadboard. When I moved it to the protoboard, it gave me the problems. I thought, maybe, the adapter got damaged or something. I then soldered on the same valued resistors in the right order, and it gave me the same output. I can't retry the adapter on a DIP chip yet since I'm waiting on new ones to arrive. All I know, is that a working adapter wouldn't work on THIS protoboard...

Bob,
My code almost looks verbatim. I simplified it and took any other code away, thinking that maybe a PWM signal "next door" on another pin could maybe screw with the NTSC signal. Negative.

Bob Lawrence (VE1RLL)

Philldapill,

If your sure that it's not the hardware wiring I would try a fresh copies of the TV and TV_Text object's ( TV Driver v1.1 ) from the object exchange. Just temporarily rename the old versions in your working directory (if any) and the library versions . Maybe you experimented somewhere along the way and changed some settings.

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Aka: CosmicBob