A uc PIC to TV circuit with ground problems

[psmll]

üç piç

Hi,

I'm playing with a PIC to generate TV signals (composite).

All seems work well, but on some TVs, for example I need to have the RF antenna plugged or the TV, to TV show well the images that PIC are sending.

I also discovered that if I connect my circuit ground to the ground of my electrical home system it also works OK.

I can't understand this, for composite connection we have only 2 wires, one for video signal and other are the ground.

I have my circuit powered by a 9V battery.

Why some TVs have problem reading the signal?

Some ideas please? And of course solutions ;-)

 

[Computerman29]

connect pic to tv

Greetings,

It sounds like interference of some kind, or a bad cable. Try a different cable. I don't know enough about what you are doing to offer any other advice. Good luck

Computerman29

 

[psmll]

I don't know enough about what you are doing to offer any other advice. Good luck

I tried some known schematics, and people says that it works, but I have always the same problem, need to connect the ground to work ok

An example schematic with 2 resistor DAC:

 

[IanP]

To receive this signal on any TV set you need a TV modulator, as these circuits (including PIC-based with 2-resistor D/A from your last post) generate baseband video signal ..

The rason why some TVs may pick-up 'something' is that this signal has a lot of harmonics (as any square wave has) but the high-order harmonics are very, very weak and you need a sneaky path (which ground-connection just happens to provide) to get them to the TV's tuner ..

You can still use this signal by connecting it to TVs' AV-input (usually with RCA connectors) and selecting LINE (or AV) input ..

Regards,
IanP

 

[psmll]

To receive this signal on any TV set you need a TV modulator, as these circuits (including PIC-based with 2-resistor D/A from your last post) generate baseband video signal ..

The rason why some TVs may pick-up 'something' is that this signal has a lot of harmonics (as any square wave has) but the high-order harmonics are very, very weak and you need a sneaky path (which ground-connection just happens to provide) to get them to the TV's tuner ..

You can still use this signal by connecting it to TVs' AV-input (usually with RCA connectors) and selecting LINE (or AV) input ..

Regards,
IanP

Hi, as I said I was using the composite input, so the signal is in baseband, no need to an modulator.

What I said is that I connect my circuit to the composite input and only get noise on image, with my circuit still connected to composite, and connecting the RF input antenna, the signal that I'm sending to composite are displayed well.

Also if I don't have the RF input antenna connected, but connect my circuit ground to the ground of my electrical system home system, he signal that I'm sending to composite are also displayed well.

I'm a bit confused, and don't know what is the problem, I will try to split ground and other things and see what happens...

 

[psmll]

Problem solved.

I'm feel quite bad, but I have to say that the problem was the breadboard

Now everithing works OK again