Broadcast mode with TV_TEXT

sharpie

So, I am left a little confused after trying to gather enough information on how exactly to get the propeller to transmit to a nearby television on channel 4 or 5, etc..· I've tried modifying the stuff as mentioned here http://forums.parallax.com/showthread.php?p=572073·...· I got it to the point where I can hold the propeller about 3 inches from the tv antenna and see a somewhat garbled screen that resembles what I was expecting.· Am I missing something, I had read that hanging just a 6-10" wire would do the trick up to about 10' away.·

Does anyone have a version of the tv_text modified to work in broadcast mode?· Or is anyone willing to point out which amazing oversight has led to my ignorance here?
Thanks...

Post Edited (sharpie) : 8/7/2006 8:52:32 PM GMT

Mike Green

I went through this earlier. It doesn't work well on channels other than 3. It has to do with the channel frequency (60MHz) being an exact multiple of the clock frequency (5MHz). If you have to have some other channel, you can try changing the crystal frequency. I also found that interlaced worked better than non-interlaced and black and white worked better than color. I never did get 10' of good range, but 2 to 3 feet did work. If you use a tuned antenna, you can get better range.

VHF analog channel spacing is 6 MHz. Changing to a 6MHz crystal would probably allow any of the lower channels to work. Even though the Propellor is supposed to work only up to 80MHz, most will work happily at 96MHz with the 6MHz crystal. You have to change your programs to include a new _CLKFREQ declaration.

Post Edited (Mike Green) : 8/7/2006 9:09:38 PM GMT

sharpie

Thanks Mike. I'm willing to use any channel I can get. 2-3 feet is acceptable (in my case preferable). What modifications did you have to make to the object to make it work?

Mike Green

Here's a modified tv_wtext that I used. I noticed that the allowable pin numbers for the start call were all multiples of 4, so I allowed the use of a channel number in the lower 2 bits of the video pin number. Look at the comments at the beginning for details.

sharpie

I see where you used %10 for 3, etc... I'm still a little confused as to how I should start your modified object. Suppose I use pin A8(1.1k), A9(560), and A10(270).... I simply do something like text.start(8) or do I need to use the binary? You can assume I am a little short on enough experience to grasp the correlation of the binary numbers with the pin numbers, etc.

Thanks for your help.