teletext decoder part 3

teletext decoder part 3 elektor deceniber 1981 — 12-29 part 3 The decoder section described in part two does have its limitations: no simul- taneous reproduction of Teletext infor- mation and the television programme; no time indication; no subtitles, etc. The video control board makes all this possible, but as indicated by figure 9, there are still a number of items to be considered. The output of this circuit can once again be connected to the video input (if present) of a television set. The amplitude of the video output signal can be adjusted to a maximum of twice the input level (by means of P8). IC24. This IC (LM 1889N) is a complete colour modulator which is able to produce a colour video signal from the luminance signal (Y, pin 13) and the R-Y and B-Y signals. The three signals needed for this purpose are not supplied by the TROM (IC10) in the Teletext decoder, this IC only produces the basic signals R(ed), G (reen) and B(lue), therefore IC20 is used as a converter. Besi...