Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "cunningfellow" <andrewm1973@...> wrote:
>
> > Joh Elson wrote:
> >
> > Note that my photoplotter as it is cranks
> > out a pixel every 5 us, so even as 8-bit
> > bytes, that is 625,000 bytes a second.
> 
> 16.384" drum
> 1000 dpi
> 600 RPM (10 r/s)
> 1 bit per pixel
> 8 bits per byte
> 
> I get 20 kilobyte per second
> 
> Am I missing something
>
Yes, probably that I wrote that in my sleep.  OK, my machine has a 6.519" diameter drum, or 20.480" circumference, and a 1024 pulse encoder multiplied by 20 to give 20480 pixels per rev, at 10 RPS.
So, that gives 204800 pixels/second.  Since this was designed to eventually allow 8 lasers to lay down 8 raster lines at a time, it now only uses one bit per byte, so the DMA port has to supply 204.8 K bytes/second, which is no problem for even an ancient PC.

Jon