If you have a camera and want to add additional data in real time to the captured image, you need to overlay your text on the original picture, most of the cases the overlay image is a low resolution text, at first I thought this would be very complicated, but after I found this project I had to change my mind. By using only the ATmega8 and LM1881 the author can overlay any text on the S-video signal.
Since high frequencies are involved the proper ground is needed to avoid noise problems, since the breadboard isn’t suited for frequencies above 10kHz, the author used a thin aluminum foil as shield, if you make a pcb keep in mind that the LM1881 is very sensitive.
The project doesn’t need any expensive components, and work even on a breadboard, the firmware is written in C and is available for download, you can easily modify it to display your custom messages. Since most of the video cards in PC’s have output in S-video format too, this device has a great potential.