video pattern generator

10-28 — elektor october 1980 video pattern generator P. Needham The original circuit of the video pattern generator (see Summer Circuits issue 1979) has been slightly modified and a printed circuit board has been designed for it. The pin numbering of the various gates has been altered, mainly to sim- plify the layout on the board, and of course the modifications published in October 1979 have been incorporated. To give a clearer indication of how the unit works, the circuit diagram has been divided into four sections which each carry out a certain function. Block A takes care of the synchronisation pulses. Block B provides the sound output and grey scale circuitry. Block C contains and a binary counter IC12b. During line and field blanking intervals the oscillator is inhibited and the counter is reset to zero to ensure that each new line is correctly positioned. The outputs of the counter are inverted by N30 ... N32 to give a descending grey scale. The grey scale is selected by ...