Circuit Lake

Electronic Project and Circuit Collection

Television Character Superimposers

12/07/2010 Category: AVR, Display, Interfacing, Microcontroller, Miscellaneous, Project

The project goal is to built low cost TV Superimposers based on ATmega88 and ATmega48. The device allows you to display numerical data, such as temperature values, or characteristic data, such as short comments about the video feed along with real-time images from a camera. The project is composed of 2 PCB boards, VSP main board and Communication board.


VSP main board

NMJ2207 extracts a composite sync signal from the entered video signal. It inputs this composite-signal to the INT0 interrupt port of ATmega88(20MHz). The INT0 interrupt handler of ATmega88 chooses a vertical sync signal, a horizontal synchronizing signal from the composite-signal. Then, it synchronizes with the horizontal synchronizing signal and it outputs the character control signal of a horizontal-scanned line from the TXD of the UART. The UART works on master SPI compatibility mode which doesn’t have a start bit and a stop bit. Each bit from the UART represents one dot of the displayed character. NMJ2207 changes the video signal output to a character Y signal level while the video signal is high. It is possible to adjust this character Y signal with the rheostat.

Communication board
ADM3202 changes the electrical characteristic of the RS232C into a TTL level. From a PC, the ATmega88 (or Atmega48) on the bottom board receives the character data that is to be imposed. The received characters are then sent to the main board of the VSP by the 2 line serial interface.

TV superimpser display on TV

This low cost TV superimposer is designed by Kazuyoshi Teramoto.

TV super imposer
Project Detail and Documentation