A nerd snipe, in which I learn to read gerber files


So, I had the realisation last night that the biggest sunk cost with getting a PCB made in China is the shipping. The boards are about 50 cents each, and then its $25 for shipping (US dollars of course). I should therefore be packing as many boards into a single order as possible to reduce the shipping cost per board.

I have a couple of boards on the trot at the moment, my RFID attendance tracker project (called GangScan), and I’ve just decided to actually get my numitrons working and whipped up a quick break out board for those. You’ll see more about that one later I’m sure.

I decided to ask my friends in Canberra if they needed any boards made, and one friend presented with a set of Gerber CAM files and nothing else. That’s a pain because I need to know the dimensions of the board for the quoting system. Of course, I couldn’t find a tool to do extract that for me with a couple of minutes of Googling, so… I decided to just learn to read the file format.

Gerber is well specified, with a quite nice specification available online. So it wasn’t too hard to dig out the dimensions layer from the zipped gerber files and then do this:

Contents of file Meaning Dimensional impact
G04 DipTrace* Comment
G04 BoardOutline.gbr* Comment
%MOIN*% File is in inch units
G04 #@! TF.FileFunction,Profile* Comment
G04 #@! TF.Part,Single* Comment
%ADD11C,0.005512*% Defines an apperture. D11 is a circle with diameter 0.005512 inches
%FSLAX26Y26*% Resolution is 2.6, i.e. there are 2 integer places and 6 decimal places
G04* Comment
G70* Historic way of setting units to inches
G90* Historic way of setting coordinates to absolute notation
G75* Sets quadrant mode graphics state parameter to ‘multi quadrant’
G01* Sets interpolation mode graphics state parameter to ‘linear interpolation’
G04 BoardOutline* Comment
%LPD*% Sets the object polarity to dark
X394016Y394016D2* Set current point to 0.394016, 0.394016 (in inches) Top left is 0.394016, 0.394016 inches
D11* Draw the previously defined tiny circle
Y1194016D1* Draw a vertical line to 1.194016 inches Board is 1.194016 inches tall
X1931366Y1194358D1* Draw a line to 1.931366, 1.194358 inches
Board is 1.931366 inches wide (and not totally square)
Y394358D1* Draw a vertical line to 0.394358 inches
X394016Y394016D1* Draw a line to 0.394016, 0.394016 inches
M02* End of file

So this board is effectively 3cm by 5cm.

A nice little nerd snipe to get the morning going.


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