555 timer compo entry 2

This entry is a 4 step sequencer controlling an `Atari Punk` synth with a greyscale NTSC video visualization of the output audio, built using two 558 quad-timers and two 556 dual-timers. Sorry in advance for the poor video quality, I will try to get a direct capture next week when I get back from GDC, but I was in a rush to make the contest deadli
555 timer compo entry 2 - schematic

ne. Soldering up all those potentiometers, switches, etc. takes a suprising amount of time. These signals are low for the time specified in the RS170 standard (3 lines for vsync, 10. 9 us for hsync), although the final result isn`t exactly up to RS170 spec. It generates a `combined` or industrial sync (which works on every TV I`ve ever tested), but RS170 requires serrating and equalizing pulses to be generated during vsync to prevent 1950s hsync oscillators from losing tracking. Each blanking signal is fed into a 558 monostable timer, which generates the blanking signal (lasting longer than the sync signal and delaying until the image is about past the overscan). The two sync signals are combined with one AND gate into a CSYNC signal and the two active signals are combined (with wired AND from the 558 open-collector outputs, but buffered into another AND gate) to generate a CACTIVE signal. One 558 quad timer serves as a 4 step sequencer, similar to a traditional use of a 4017 decade counter. All four steps use the same timing components, but the overall step rate is controlled by varying the control voltage for the 558 timer. You can chain several 558`s together to get longer sequence lengths, but I only ended up wiring switches and pots for 4 steps. The output of the sequencer is combined with the `left` potentiometer of an atari punk synth implemented in the other 556 (conflating the two for the timing of the astable...

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