AVR composite PAL color bar generator
Here’s a fun AVR project, a 6 bar color pattern for a TV (source and schematic included). Serasidis writes –
I start this project 3 weeks ago, because I was wonder ” is that possible, some AVR MCU to create simple colour bars? ” At the beginning I believed that its easy. So, I ask some people who they knew more about PAL composite video signal. Some of them told me that is impossible to product color entire-in-software with AVR MCU (microcontroller) because there is not enough power (frequency).
The first idea they was to work with 8.867238 MHz crystal (2 times the color carrier). When I read more about PAL video composite signal creation, I saw that, if you want to product colors entire-in-software you must to create the color-carrier (4.43 MHz), to change 4 times the phase of color-carrier (one time for each color), to show 4 colours. Except that, you have to change the color-burst from 135 deg to 135+90= 225 deg.
So, the 8.86 MHz its not enough, that`s why I used 17.7 MHz crystal (4 times the color carrier). The only easy is to create the white and the black bar, the rest of this project, beleave me, its not easy.
The timing (clock cycles) of any instruction is very important for the phase-shift of the color-carrier and color-burst signals. Calculate the cycles before add or remove any instruction.
AVR composite PAL color bar generator – Link.
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