Again within the Eighties, printers had been costly issues. Scanners had been uncommon, notably for the house market, as a result of dwelling computer systems may barely deal with fundamental graphics anyway. Again in these halcyon days, an obscure firm referred to as Thunderware constructed a tool to transform the previous into the latter. It was referred to as the Thunderscan, and was a scanning head constructed for the Apple ImageWriter dot matrix printer. Bizarre sufficient already, however this gadget hides some bizarre secrets and techniques in its design.
The precise scanning technique was easy sufficient; the gadget mounted a carriage to the printer head of the ImageWriter. In that carriage was an optical reflective sensor which was scanned throughout a web page horizontally whereas it was fed by the printer. Thus far, so regular.
The hilarious half is how the scanner truly delivered information to the Macintosh pc it was hooked as much as. It did exactly nothing with the serial information traces in any respect, these had been left for the pc to command the printer. As a substitute, the output of the analog optical sensor was fed to a voltage-to-frequency converter, which was then hooked as much as the handshake/clock-in pin on the serial port.
The scanner software program merely seemed on the price at which new characters had been changing into out there on the serial port because the handshake pin was toggled at numerous frequencies by the output of the optical sensor. Sooner toggling of the pin indicated a darker part of the picture, slower corresponded to lighter.
Curiously, [Andy Hertzfeld] additionally has his personal tales to inform on the event, for which his software program contribution appears to have netted him an ideal sum of royalties through the years. It’s humorous to suppose how mainstream scanners as soon as had been; and but we barely take into consideration them right now past a number of area of interest makes use of. Occasions, they alter.
Because of [J. Peterson] for the tip!