Homebrew PCBs

> Russell wrote:
> 
> At the data rates needed, you'll need
> to store the whole file in the machine
> controller.

I was only planning on storing 1 row/
scanline of data at a time.

> A 300mm drum has a circumference around
> 1000mm.  Assume a pixel size of 0.01mm.
> If it rotates at 600rpm, the pixel rate
> is 1Mpixel/sec.   A 100mm x 100mm plot
> will need 1000s or 17mins to scan. The
> averaged pixel rate will be 100k pixels
> /sec.  The file size will be 100Meg
> pixels, which is impractical.

> The pc could send bitmap data while the
> machine is running, if the data rate is
> higher than 100k bits/sec.  Fast rs-232,
> usb, or ethernet could do that.

I was planing on a 16.384 inch active
area on a 20 inch or so round drum that
is 10 inches long.

(no prizes for guessing why I chose the
active area to be 16.384 inches)

2000 dpi (about 0.01mm) resolution.

It ends up being a file size of 35
megabytes.

I think the data rate I worked out I
wanted was 800 kilo baud RAW.

An FT232 sitting on a USB port can do
this.  But its going to be a strain on
the poor Atmel to keep the throughput.

Most PCB files compress better than
10:1 with G3.

If I G3 compress it I can get by with
much lower baud rates (sub 100 kilobaud)

CRC on a 1 megabaud link will take
more time than CRC on a 100kilobaud
link and G3 decompression together.

I think the ATMEL has enough omph
for either - but i like the idea of
keeping horsepower spare in case I find
there is something else I need to do.

Worst case senario and I am prting out
a bit map for a T-Shirt and I don't
get 10:1 compression - it just runs
slow.

Because the atmel has enough memory to
buffer one full scan line - it wont
BREAK the thing - it just will mean it
has to pause between scanlines. (one
hour to print instead of 10 minutes)