It is impossible to make a modern video card at home. But any home craftsman can build its demonstration layout. It connects to a COM port of a computer and displays a black and white image on a regular TV, without conflict with the main video card of the machine.
Instructions
Step 1
Build any level converter for the COM port, for example, on a MAX232 chip or similar. If your computer does not have a COM port, build a USB-COM converter with TTL output levels, for example, on the FT232 chip.
Step 2
Take an ATmega8 microcontroller. Write the firmware from the following archive into it:
Step 3
Connect pins 8 and 22 of the microcontroller with a common wire, 7 and 20 - with a positive power supply. Connect one blocking capacitor with a capacity of 100 nanofarads between pins 7 and 8, the other between pins 20 and 22.
Step 4
Switch on a 16 megahertz quartz crystal between pins 9 and 10 of the microcontroller. Connect each of its terminals to a common wire through a 22 picofarad capacitor.
Step 5
Make two chains, each consisting of a 1N4148 diode (KD522) and a resistor (cathode to resistor). The first resistor should be 1k ohm, the other 330 ohm. Connect the anode of the first diode to pin 15 of the microcontroller, the second to pin 17.
Step 6
Connect the free leads of the resistors together, and then connect them to the common wire through a 56 Ohm resistor. Connect the resistor connection point to the center contact of the video input connector of the de-energized TV, disconnected from the collective antenna, and connect the common wire of the homemade video card to the ring contact of this connector.
Step 7
Pins 2 and 14 connect together and connect to them the output line of the converter, which receives data from the computer. Connect the converter itself to the computer.
Step 8
Supply power to the video card from the Molex connector of the computer, if it works from a COM port (5 V is required, but in no case 12), or directly from the power bus of the USB port, if the device operates from it.
Step 9
Set the jumpers between the common wire and pins 23 - 28 of the microcontroller in accordance with the following table:
Step 10
Turn on your TV and computer. On the TV, select the video input to which you connected your homemade video card. After the computer boots up, launch any terminal program, select the port to which the device is connected (set its parameters in accordance with the configuration of the jumpers), and then output any Latin text to the port. If done correctly, your text will appear on the screen.
Step 11
Write a program that outputs the text automatically yourself, say, in Python. Now you have a second video card that works independently of the main one and allows you to display text on a second display device independently of the main monitor.
