Propeller backpack--noise in video overlay

nathanww

Hello all,

I am currently using a Propeller Backpack to and the tv_overlay2 module to embed data from sensors into a video feed during a neuroscience experinment. Basically, I have a rat cage with a camera mounted in it, which transmits NTSC video through the Backpack to into a DVR. The propeller is used to overlay a time stamp and also a representation of all the states of the sensors in the cage. The idea is that specific behavioral events can then be decoded from the video.

Unfortunately, the Backpack seems to be introducing a lot of grainy noise into the signal. The noise seems to be intrinsic to the chip (I've tried using a better power supply and putting it in a shielded box) and is messing up the ability of the program to decode video. I'm also pretty sure that it's not a sync extraction issue (which was happening, but was fixed by adding an appropriate load)

Have any of you had succsess in reducing the amount of noise introduced by this board? I'd love to hear any suggestions you might have.

Phil Pilgrim (PhiPi)

Can you snap a photo of the video image and post it here?

-Phil

nathanww

It's actually a bit hard to see in a still picture, but what is happening is that the image is generally grainy and also has some faints bands slowly moving from the top to the bottom.

Phil Pilgrim (PhiPi)

It could be that with the additional load resistor your signal levels are too low. One thing you could try is to eliminate the load resistor and go to a semitransparent overlay, rather than the opaque one you're using now. That would allow the incoming video signal always to see the 75-ohm termination of the monitor so that the Backpack can keep it in sync. The better option -- although it costs money -- is to replace the video camera with one that outputs a signal at the proper impedance (i.e. 2V p-p @ 75 ohms without a load) so as not to overload the Backpack's sync detection circuitry.

-Phil

msrobots

nathanww,

welcome to the forum.

Phil is the expert for the BackPack. He build this wonderful board. I struggled also with it and found that using a slightly better camera solved all problems I had.

anyways - where is the rat?

Hiding?

Mike

nathanww

Thanks! The camera right now is a super-cheap board camera that's the standard one installed in the cages so I'll try swapping it out for a better one and see if I can get more signal without losing sync.

And there's no rat because I went down there between training sessions--anytime there are animals in the room we have to wear gloves and that's not ideal for futzing about with electronics.