This project really pushes 8-pin PIC microcontroller to its limits. It takes only few elements and can do really cool things with your PAL TV screen. It simply adds various text effects to PAL composite video signal in real time.

Circuit is overclocked with 25MHz crystal and it works fine. Super imposer uses same video signal to synchronize itself by detecting 28us low level pulse in comparator input. After synchronization, super imposer sends text constructed from 5×7 elements stored in RAM memory. Only two colors can be imposed – black and white. Project files are here. You can also see working Super imposer Youtube video.