Video overlay circuit with ATmega8 - OSD
Video overlay is a technique of displaying a video information on a screen that's already displaying some image or a video. This technique is usually used in OSDs (on-screen display).
To display anything over an existing video signal you would need an IC that is built just for that purpose, such as teletext chips that display teletext info on a TV or even MAX7456 OSD chip. In this project, only ATmega8 is used to generate data and mix it with the existing video signal. Along with microcontroller there is also an LM1881 circuit that is used to extract timing information (sync) from the original video signal. This additional IC simplified the firmware in microcontroller.
Similar project but without the LM1881 can be found here.
© Gary N. Dion