--- In
Homebrew_PCBs@yahoogroups.com, "designer_craig" <cs6061@...> wrote:
>
> John,
> Thanks for the info, that is exactly what I was thinking but will most likely use some aluminum tubing for the drum. With the size and cost of memory these days I was planning on using a little Atmel uP possibly assisted by a FPGA to buffer up a full sheet worth of data prior to writing the drum.
>
> My initial thoughts were something like 600 dpi do you find you need the 1000 dpi?
Yes, if I could have found the right size aluminum tube, I might have used that to start. Something slightly over 6.5" just didn't seem available. I guess I could have rolled some thick sheet, but even the roller at work probably could not have handled 1/4" thick aluminum.
A 12 x 16" sheet of film would take 192 MB of memory. What I would probably do now is either use the parallel port in DMA mode, or use something like the Cypress FX2 (EZ-USB) chip (a fast USB chip that is marginally programmable, and can stream byte-wide data at incredible speeds. I got one at work, I wasn't able to program it to do what I wanted, but I think it could run a photoplotter pretty well.
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.
Yes, the 1000 DPI is really marginal for PCB work, I routinely make .008" lines and spaces. Even the cheap photoplotters do 2500 DPI and the more expensive ones are 10,000+.
Jon