TV signal generator on a microcontroller. Signal generator for adjusting televisions - Television equipment - Schemes of household devices. Schematic diagram of a TV signal generator

Dendy is a generator of test television signals. A new version

A homemade cartridge for the Dendy video set-top box, which turns it into a television test signal generator (GITS), has interested our readers. Thanks to their feedback, the author of the design and program, S. Ryumik from Chernigov, was awarded an incentive prize in the “Best Publication of 2001” competition. Today we present GITS-2 - an improved version of the cartridge.

Compared to the first version of the proposed device, the scope of its application has not changed - setting up and adjusting color (operating in the PAL system) and black and white TVs, assessing the quality of the kinescope when buying a TV, generating test tables for cable television. However, the number of test images created by GITS-2 has been increased from 81 to 466 (taking into account all color options), and sound test signals - from two to four. In some characteristics, GITS-2 is superior to the well-known generators "Electronics GIS 02T" and "Laspi TT-03".

Since all the functions of the test signal generator are implemented in software, during modification it was necessary to change only the program. The hardware part of the device - the cartridge board itself with panels for two EPROM chips - could remain exactly the same as in the original version. However, it has also undergone a slight improvement, allowing it to work even with partially faulty Dendy consoles.

GITS-2 board diagram shown in Fig. 1, differs from the original by an additional XT3 jumper, which serves to switch the screen pages of the Dendy video processor.

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If one of the video pages in your set-top box is faulty (extra lines or squares are visible on the image), you can switch to another by moving the jumper and pressing the SELECT button on the joystick. In position "1" the first page of video memory works, in position "2" - the second page of video memory.

Drawings of printed conductors and the arrangement of elements on the cartridge board are shown in Fig. 2.

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The shape of the board was chosen based on the convenience of its installation in a standard Dendy cartridge case. A narrower board without side cutouts will not be able to be fixed in it. Therefore, you should not save material by reducing the width of the board.

The case is taken from a game cartridge that has become unusable. Sometimes you have to modify it a little, for example, shorten the plastic pins inside.

When developing the GITS-2 program, the author sought to implement the maximum number of tests, occupying no more than 2 KB of ROM. In particular, the image of the test table is stored packed according to the original algorithm. Compression ratio - 50.2% (from 960 to 482 bytes). At the same time, the data unpacking subroutine took only 57 bytes. To store the same data packed using the ZIP method, it would require only 435 bytes, but the length of its unpacker is many times greater.

The codes that need to be entered into the RPOM DS1 and DS2 with an information capacity of 2 KB each (KR573RF5 microcircuits or their analogues) are given respectively in Table. 1 and 2.

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The properties of GITS-2 (as well as GITS of the first version) do not depend on the type and capacity of the ROM chips used, so the latter can be combined on the board in various combinations, not forgetting to just install the XT1 and XT2 jumpers in the required positions. If you do not plan to replace microcircuits during the operation of the cartridge, you can connect the corresponding contact pads on the board with ordinary wires instead of jumpers.

On the new board (with the HTZ jumper in position “2”), microcircuits programmed in accordance with . But they need to be used as a set: both “new” or both “old”. Naturally, in the latter case, GITS will have only the properties that were described in the original source.

If you have a ready-made board of the old version of GITS, in order to use all the tests described below, it is enough to install in its panel RPOM chips programmed in a new way.

Those wishing to make their own additions and improvements to the program will be helped, which describes in detail the methodology for developing programs for "Dendy"

DESCRIPTION OF TESTS

After installing the GITS-2 cartridge in the “Dendy” and turning on the power, a test pattern should appear on the TV screen (top picture on the 1st page of the cover) and a trill should sound. If there is no image, but there is sound, try moving the HTZ jumper on the cartridge board to a different position, press the SELECT button on the joystick. This operation allows you to switch from a possibly faulty video page to a working one. If there is no sound, some of the main RAM cells of the game console used by the program have probably failed and further work is impossible.

Due to the peculiarities of the "Dendy" video system, it is difficult to form exact squares on the TV screen (it is not possible to fit into the given amount of ROM). Therefore, in all test images they appear as rectangles with an aspect ratio of 4:5. However, the central circle of the test table has the correct shape, which makes it possible to evaluate the geometric distortions of the raster and adjust its dimensions. In addition, the table allows you to center and focus images using five reference marks in the center and corners of the screen, and check horizontal and vertical clarity (200...250 lines on a fine grid). There are areas with a checkerboard field, colors, and diagonal lines. When you press the UP, DOWN buttons of any of the joysticks, the image is inverted (the second picture from the top on the 1st page of the cover), small inscriptions appear in the center, top and bottom of the screen.

The next 11 test images are accessed using the LEFT and RIGHT buttons. Each has four options, switchable using the UP and DOWN buttons. The options, in turn, have from two to 24 varieties: button A changes the color of the image, button B inverts it, or turns on/off the fine grid superimposed on the main image. The START button switches sound test signals. The transition from one test to another is accompanied by a “beep” sound, and the beginning of a new cycle of their change is accompanied by a trill.

Vertical color stripes (Fig. 3, a) - eight stripes of the same width in the following order (from left to right): white, yellow, blue, green, purple, red, blue, black. They allow you to check the correctness of matrixing, adjust the contours of pre-emphasis correction, and evaluate the color saturation in adjacent rows. The shades of the generated colors depend on the characteristics of the Dendy video processors of different models and may vary slightly. Options: replacing primary colors with additional colors, turning off color (gray scale, third picture from the top on the 1st page of the cover). Varieties: Letter C on blue stripe for easy identification.

Horizontal colored stripes (Fig. 3, b, c) - eight stripes similar to the vertical ones, but the lowest one is half as tall.

Uniform gray field. Allows you to check and adjust static white balance and color purity. Options: four gradations of brightness. Varieties: cyclic image inversion with a period of 2 s, which allows you to check the quality of image size stabilization and the stability of synchronization of frame and horizontal scans. When you press and hold button B, the “blinking” frequency quadruples.

Uniform red field. Serves to check color purity and identify defects in the kinescope mask (there should be no white dots in the image). Options: four gradations of saturation. Varieties: “blinking” with a period of 1 or 2 s.

The uniform green field is similar to the red one.

The uniform blue field is similar to the red one.

A checkerboard field of black and white rectangles (16 columns, 15 rows) allows you to evaluate the linearity of scans, geometric raster distortions, and check the absence of color borders. Options: inversion of the image, doubling the size of the rectangles (bottom picture on the 1st page of the cover). Varieties: a fine grid superimposed on the image, replacing white with one of 12 possible colors (Fig. 3, d).

Monochrome stripes (“sailor suit”, Fig. 3, d) are used to evaluate the linearity of the scan and the uniformity of coloring of extended sections of the screen. Options: vertical or horizontal stripes, doubled stripe width, image inversion. Varieties: a fine grid superimposed on the image, replacing white with one of 12 possible colors (Fig. 3, f).

Dot field (Fig. 3, g). White dots (15x16) on a black background with a marker in the center serve to check the focusing and astigmatism of the electron beam over the entire screen area, as well as the static and dynamic convergence of primary color beams. Options: halved or doubled or quadrupled the dot pitch (you can choose the optimal one depending on the size of the TV screen). Varieties: image inversion, replacement of white with one of 12 possible colors (Fig. 3, h).

A grid field of 15x16 thin white lines on a black background is used to adjust the convergence of red, green and blue beams and check focus. Options: halved or doubled and quadrupled grid spacing. Varieties: image inversion, replacement of white with one of 12 possible colors (Fig. 3, i, j).

Audio test tones are used to check the TV's audio channel. The following signals are provided, switched cyclically by the START button: rectangular pulses with a duty cycle of 2 ("meander") with a frequency of 500 Hz, sawtooth pulses with a frequency of 6600 Hz, rectangular pulses with a duty cycle of 4 with a frequency of 6600 Hz, "siren" - "square wave" of a linearly varying frequency (from 27 to 12500 Hz for 9 s).