PC terminal using a TV

When you use microcontrollers in your designs, sometime you face a problem how to show user required data. Several LEDs, 7 segment display or LCD module can be solution. But if you must show a lot of information simultaneously, it can be difficulty. Large LCD modules are expensive and graphic modules require complicated control. You can solve it with a help of PC. Just send data via serial line to the computer and display everything on computer's display. I have had to solve the same problem some time ago. I have chosen normal small TV set for that. A lot of families change TV in this time because of digital broadcasting or modern flat and slim LCD and plasma displays. So they put older TV set away and it is dormant somewhere. Or you can buy older TV very cheap.
PC terminal using a TV - schematic

PC terminal using a TV - img1

The display unit must be maximum easy. For data displaying is text mode with semigraphic mode sufficient. Just only 1 integrated circuit - microcontroller - must guarantee every function of the unit. A keyboard will be useful for data input. "Button by button" assembling of keyboard is complicated and mechanical design is a weak point in hobby construction. Special keyboards are usually inaccessible or expensive. That's why I have chosen standard IBM PC keyboard. PC keyboard solves as design as character variability - there are all characters on keyboard. Economic view is very advantageous and accessibility is almost unbeatable. The size is disadvantage of PC keyboard but beside TV set it doesn't matter. I have developed 2 versions of TV terminal. "Built-in" version is designed for utilization in device. The second version is standalone device with external power source. The described TV terminal accomplishes these results: Display mode: black and white Text mode: 40 characters x 25 lines Semigraphic mode: 80 x 75 "points" Printable characters: ASCII 32 - 127 Keyboard: IBM PC AT compatible Control characters: 11 Serial line speeds: 1200 Bd to 115.2 kBd Power supply: 9 - 12 V or 5 V (built-in version) Current consumption: cca 30 mA + keyboard consumption As you can see wiring diagram is very easy. Most of the functions are centred in the microcontroller U1. There must be minimally 1 kB RWM for 40x25...

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