help printing pcb layout

[angrykoko]

I want to etch this: http://apocalypseaudio.blogspot.com/2010/02/toecutter-v1-revc-pcb-layout.html?m=1

But not knowing the dimensions is proving to be an issue.
I tried setting it to 300 dpi in gimp print size dialog but it's still to big. 
Usually,  I just keep raising the dpi until it seems to print correctly but, it's a horrible waste of paper and ink so I thought I ask you guys what I'm missing when it comes to getting these types of layout images to print.

Thanks
Koko

[RobA]

How much too big was it? I took the image into Pixelmator and measured the pixel count between the centers of the two leads for the C1 cap. The leads should be 0.2" and I measured 80 pixels. That would make it 400 pixels per inch. That's a weird number, but if 300DPI is is just a bit too big, that might be the right value.

[angrykoko]

Thanks RobA,

At 300 dpi C1 would measure between 6 and 7 mm when I printed, and the whole overall pcb is obviously just too big  (like an inch too long, 1/2 ingh too tall).   

@ 400 dpi C1 looks dead on 5mm centers and the overall board looks correct so your calculations work

Now, to figure out how (if even possible) to measure pixel counts between two points in GIMP.
Thanks for the tip of getting pixel counts and doing that math.. I would have never thought of it.

I was really tired of my guessing at things until they seemed right.


Koko

[Thomas_H]

IF you use Irfanview (free) you can set the DPI of an unknown image and try printing it in different sizes.

[RobA]

Thanks RobA,

At 300 dpi C1 would measure between 6 and 7 mm when I printed, and the whole overall pcb is obviously just too big  (like an inch too long, 1/2 ingh too tall).   

@ 400 dpi C1 looks dead on 5mm centers and the overall board looks correct so your calculations work

Now, to figure out how (if even possible) to measure pixel counts between two points in GIMP.
Thanks for the tip of getting pixel counts and doing that math.. I would have never thought of it.

I was really tired of my guessing at things until they seemed right.


Koko

Glad that helped. I think the measurement would have come out to 6.333 mm if a 400 DPI image were printed at 300DPI.

When I looked at the info for that image, it listed it at 72DPI. I think that's a default when no resolution info is given in the file.

I just downloaded GIMP to take a look. I didn't know that they had made a native Quartz port for OS X. It might be a more useful tool for me to have around now. Anyway, there's an icon in the tool pallet that looks like a compass, I guess it's supposed to look like a pair of dividers. It's the measurement tool. If you select it and click and drag across the points you want to measure, it displays the pixel size and angle in a display area.

[angrykoko]

Oh yeah.. I see it now.

Thanks Again!

[davent]

If i remember correctly i've load pcb images into Inkscape, set the background grid to .10" and then use scaling to adjust the pcb size until say, an IC's pads align with the .10" grid, should be good to go.