I have learned some thing about TV in one of my B.tech semester but I forgot most of them. Now I refreshed a few basics and tried to implement a monochrome PAL TV signal generator using an AVR micrcontroller. I was using PIC earlier but later I jumped to AVR because I loves the USBASP programmer, the free avr-gcc compiler and the user friendly architecture of AVR microcontroller .Also at any time, if I feel little bit lazy, they I can try arduino also.
At first, my aim was to display few A B C D letters on my tv screen. But it is not possible for a beginner to do it directly(at least in my case) without doing any hello world stuff on TV. The first and the basic hello world pattern which one could display very easily on his tv is a vertical line of desired thickness and position. This is very easy because we don’t need to provide any vertical synchronization to lock the picture scrolling on vertical axis, what we need to provide is a horizontal synchronization only.
We need to display a picture exactly on it’s position relative to the coordinates of the tv display. ie we need to lock a picture frame on the screen and it should not vibrate or move up and down or it should not disturb the scanning rules. For this along with the analog picture data (.3 to 1v), we send few digital data of 0 – 0.3 v levels which do the synchronization process. There are two synchronizations , the horizontal synchronization and the vertical synchronization.
Horizontal synchronization pulse in the signal makes it synchronized with the horizontal scanning. Similarly vertical synchronization pulses(a stream) makes it synchronized in the vertical direction , this ensures that the picture always starts from the top on each field(each interlacing fields) and locks the picture on the screen on it’s exact position. Vertical synchronization is a long compared to horizontal synchronization. For more Detail: AVR based monochrome signal generation for a PAL TV Using atmega16 micrcontroller