Apropos. I made TV-surveillance unit when 555 was almost brand new. Maybe 1977. The start of a picture was long negative pulse, easy to recognize with 555, whic

Apropos. I made TV-surveillance unit when 555 was almost brand new. Maybe 1977. The start of a picture was long negative pulse, easy to recognize with 555, which triggered second 555, which triggered third 555 in unison with the horizontal scan pulse. Thus you had fairly accurate point selected in the screen, showing a dot, while camera info was sampled and compared to a preset value. Thus the watchmen could use few knobs and select a point in the screen, which would raise an alarm when illumination changed. Because it was so cheap, you could select multiple triggering points. No fancy microprocessors this time, which were too slow anyways.