Dummy video input?

[TheNorm]

Is there an easy way to fake input so I can put data up on an otherwise blank screen?

[Michael]

I don’t know of an easy way. The signal needs to have the correctly timed vertical and horizontal sync signals. How about an old VCR or DVD player?

[TheNorm]

As I read further it looks like the original tvout will do what I’m talking about. I could make a duino for the tvout and mount it on top of your board. The remaining questions are; can I switch between video inputs electronically and can I use a cheap oscillator on the duino or do I have to use a crystal?

[Michael]

You are correct that TVout will generate a normal black signal. You don’t need another Arduino — the VE shield goes on top of an Arduino. By setting the SYNC SELECT jumper to D9, then you can use the TVout library to generate the video output and just overlay white on top. You get white on black. This is an alternative to overlaying onto an input video image.

Make sense? See the table on this page about the settings: http://nootropicdesign.com/ve/

[TheNorm]

Apparently my board wasn’t acting to spec. I was able to get the demo output over a blank screen by switching output select to sync only, and the mixed output on overlay but d9 input didn’t work, I had to use an external source, I guess for the sync signal. Now I’m not getting program output in either mode. In overlay mode I get the unchanged input video and in sync only I get nothing.

[Michael]

I’m sure the board is fine, as it is very simple. This is a code issue.

If you are trying to produce a video signal on the Arduino (no input source), set the OUTPUT SELECT switch to “SYNC ONLY”. And set the SYNC SELECT jumper to D9.

Now run a program that has no overlay initialization in it. Just use a simple TVout program like the examples that come with the library. Do not include any Video Experimenter code in your program. Remove these functions:

// Initialize ATMega registers for video overlay capability.

// Must be called after tv.begin().

void initOverlay() {

TCCR1A = 0;

// Enable timer1.  ICES0 is set to 0 for falling edge detection on input capture pin.

TCCR1B = _BV(CS10);



// Enable input capture interrupt

TIMSK1 |= _BV(ICIE1);



// Enable external interrupt INT0 on pin 2 with falling edge.

EIMSK = _BV(INT0);

EICRA = _BV(ISC11);

}



// Required to reset the scan line when the vertical sync occurs

ISR(INT0_vect) {

display.scanLine = 0;

}

The output of the TVout program (white on black) will be displayed.

If you want to overlay the TVout output onto an input signal, you run different code than if you just want to use the Arduino as the source of the video.

[TheNorm]

Must have a solder bridge or something.
It’s dead Jim.

[Michael]

Did the board ever work? Then it stopped?

If you are in the US, I am happy to send you another LM1881 chip if you want. Just let me know.

[TheNorm]

But it should run the regular TVOut stuff without the chip, right? So that isn’t it. I must have screwed up the board somehow. I’m getting the black screen but no text.

When I first tried the board it worked as expected but needed an external video source even on ‘sync only’.

[Michael]

Yes, the TVout code without the special VE initialization code should generate output with:

SYNC SELECT = D9
OUTPUT SELECT = SYNC_ONLY

This does not need the LM1881 to function. But it’s hard to imagine how the board could spontaneously fail. It’s so simple, and the components are simple.

[TheNorm]

I found the problem. It was a bad solder joint on D1. It’s amazing how long I had to stare at the board before I saw it.

Thanks for your time.

[TheNorm]

So, how can I switch from sync only to overlay and d1 to v input in software. I assume I’d need more hardware.

[Michael]

That’s great! Have fun!

[Author]

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