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On-Screen Display Board

What it does:

This device uses the same kind of on-screen display chips that are used in things like VCR's and TV's. One end of this board plugs into your computer's RS232 (serial) port, the other end plugs into your TV's RCA video-in port. By sending it data from the computer, you can control the text (and ASCII graphics) that gets displayed on the screen. In the pictures below, I am using a small color LCD display, but this will work for any television or VCR with a RCA video-in plug. It can also overlay the same text onto in incoming video signal.

Hardware involved:

The OSD chip that I am using is the SGS-Thomson STV5730A. It is capable of displaying 11 rows x 28 characters on a standard television. Here is the datasheet for it.

The whole thing is controlled with a PIC Microprocessor.  The PIC16F628 costs less than $4, and has tons of features, including an internal 4 MHz oscillator, USART pins, 16 possible IO pins, 2048 bytes of flash program memory, 224 bytes RAM data memory, and 128 bytes internal EEPROM data memory. With speeds up to 20 MHz. Here is the datasheet for it.

I use a MAX232 chip on this board to convert the RS232 signals from the computer to TTL, (5-volt logic) which the PIC can understand.


Here is the source code for the PIC processor. The code is written in
Hi-Tech PICC Lite. This is the freeware version of thier compiler.

Here are the PCB Gerber files that I used to for this board. The PCB was designed using Protel 99.

Here is a test application written in QBasic. It will display what you type, or load the contents of a text file and display that on the screen.

Some action shots:

  email me at nullvalue@bbsmates.com